SYSTEM  OF  INSTRUCTION 


rsr 


QUANTITATIVE     CHEMICAL 

ANALYSIS. 


BY 

DR.  C.  KEMIGIUS  FRESENIUS, 

PROFESSOR   OF  CHEMISTRY  AND   NATURAL  PHILOSOPHY,   WIESBADEN. 


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EDITED    BY 

0.  D.  ALLEN,  PH.D., 

PROFESSOR  OF  ANALYTICAL  CHEMISTRY  AND   METALLURGY   IN  THE  SHEFFIELD  SCIENTIFIC  SCHOOL 

YALE   COLLEGE. 

WITH  THE   COOPERATION   OF 

SAMUEL  W.  JOHNSON,  M.A., 

PROFESSOR    OF    THEORETICAL   AND    AGRICULTURAL    CHEMISTRY    IN    THE    SHEFFIELD    SCIENTIFIC 

SCHOOL. 


NEW  YORK: 

JOHN   WILEY   &   SONS, 
15  ASTOR  PLACE. 

1881. 


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COPYRIGHT,  1881, 
BY  JOHN  WILEY  &  SONS. 


S.  W.  GRMN'S  SON, 

Printer,  Electrotyper  and  Binder, 

74  Beekman  Street,  New  York. 


EDITORS  PKEFACE 

TO  THE  SECOND  AMERICAN  EDITIOK 


IN  the  preparation  of  this  edition  of  Fresenius'  Quantitative 
Analysis,  the  general  plan  announced  by  the  editor  of  the  first 
American  edition  in  the  preceding  preface  has  been  followed. 
Although  the  original  work,  as  it  appears  in  the  last  foreign 
editions,  has  been  somewhat  abridged,  it  is  believed  that  little 
which  is  useful  to  the  student  has  been  omitted  from  the  present 
work.  All  processes  which  are  described  are  given  with  the  full 
details,  and,  with  few  exceptions,  as  far  as  practicable  in  the  lan- 
guage used  by  the  author. 

The  desired  reduction  of  the  bulk  of  the  original  treatise  has 
been  effected  by  the  omission  of  one  or  more  processes  when 
several  are  given  for  the  same  purpose,  or  more  rarely  by  the 
entire  omission  of  a  whole  subject. 

The  subjects  omitted,  in  addition  to  those  mentioned  in  the 
preceding  preface,  are  :  "  The  Determination  of  the  Equivalent  of 
Organic  Compounds,"  "The  Assay  of  Silver  Ores,"  and  "The 
Assay  of  Gold  Ores."  On  the  other  hand,  many  new  processes 
and  modifications  of  old  processes  appearing  in  the  recently  pub- 
lished first  volume  of  the  sixth  German  edition  are  included,  and 
may  be  regarded  as  valuable  additions  to  the  General  Part. 

Additions  made  by  the  editors  are  usually  distinguished  by  en- 
closure in  brackets  [  ]. 

The  more  important  additions  of  this  kind  are  in  those  chap- 
ters (in  the  Special  Part)  which  treat  of  the  analysis  of  products 
pertaining  to  the  Metallurgy  of  Iron  and  to  Commercial  Fertilizers. 

The  entire  chapter  on  the  latter  subject  has  been  prepared  by 
Professor  S.  W.  Johnson  and  Dr.  E.  H.  Jenkins,  Chemist  of  the 
Connecticut  Agricultural  Experiment  Station.  It  describes  the 

374258 


IV  PREFACE. 

methods  and  plans  of  analysis  adopted  in  that  institution  after 
much  experience  and  research. 

The  new  system  of  chemical  notation  and  nomenclature  is 
employed  throughout  the  book,  although  the  old  system  is  still 
retained  even  in  the  last  foreign  editions.  It  is  confidently  be- 
lieved that  this  change,  so  long  deferred  for  reasons  perhaps 
sufficiently  valid,  can  at  the  present  time  be  made  with  advantage 
-to  the  student  and  instructor. 

The  editor  is  under  obligation  to  Messrs.  W.  J.  Comstock  and 
A.  B.  Howe,  Ph.D.,  instructors  in  the  Sheffield  Laboratory,  and 
to  Professor  W.  G.  Mixter,  of  the  Sheffield  Scientific  School,  for 
information  and  advice  which  their  experience  has  en;  bL'd  them 
to  give  regarding  many  processes,  and  for  valuable  assistance  in 
various  other  ways. 

The  task  of  preparing  this  edition  was  undertaken  and  carried 
out  with  the  generous  co-operation  of  Professor  S.  W.  Johnson. 
To  him,  therefore,  most .  especially  are  due  thanks  from  the  editor 
and  from  those  who  may  believe  that  they  find  any  advantage  in 
the  possession  of  the  book  in  its  present  form. 

O.  D.  ALLEN. 
SHEFFIELD  LABORATORY  OF  YALE  COLLEGE,  Feb.,  1881. 


EDITOK'S  PKEFACE 

TO  THE  FIKST  AMEKICAN  EDITIOK 


IN  preparing  this  edition  of  Fresenius'  Quantitative  Chemical 
Analysis,  the  editor  has  sought  by  various  changes  to  adapt  it  to 
the  wants  of  the  American  student. 

The  foreign  editions  have  attained  such  encyclopedic  dimen- 
sions as  to  occasion  the  beginner  no  little  confusion  and  embarrass- 
ment. For  this  reason  the  bulk  of  the  work  has  been  considerably 
reduced.  A  few  processes  which  the  editor's  experience  has  con- 
vinced him  are  untrustworthy,  and  many  more  that  can  well  be 
spared  because  they  are  tedious  or  unnecessary,  have  been  omitted. 
The  entire  chapter  on  Analysis  of  Mineral  Waters,  excellent  as  it 
is,  has  been  suppressed  on  account  of  its  length,  and  because  the 
few  who  have  occasion  to  make  detailed  investigations  in  th^t 
direction  have  access  to  the  original  sources  of  information. 

The  section  on  Organic  Analysis  has  been  reduced  from  sixty 
to  thirty  pages,  mainly  by  the  omission  of  processes  which,  from 
their  antiquity  or  inferiority,  are  more  curious  than  useful.  The 
chapters  on  Acidimetry  and  Alkalimetry  have  been  likewise  greatly 
condensed,  and  all  that  especially  relates  to  Soils  and  Ashes  of 
Plants  has  been  left  out.  The  recent  appearance  of  an  excellent 
special  treatise  on  "  Agricultural  Chemical  Analysis  "  by  Professor 
Caldwell,  of  Cornell  University,  justifies  the  last-mentioned  omis- 
sion. 

On  the  other  hand,  some  important  matter  has  been  added. 
Bunsen's  invaluable  new  methods  of  treating  precipitates  are 
described  in  his  own  (translated)  words.  Yarious  new  methods  of 
estimation  and  separation  are  incorporated  in  their  proper  places. 

The  editor  thankfully  acknowledges  his  indebtedness  to  several 
gentlemen  for  special  contributions  to  this  work,  viz. :  To  Dr.  J". 
Lawrence  Smith,  who  has  kindly  furnished  a  manuscript  account 


Vi  PREFACE. 

of  his  admirable  method  of  fluxing  silicates  for  the  estimation  of 
alkalies.  To  O.  D.  Allen,  Esq.,  late  chemist  to  the  Freedom  Iron 
Works,  Lewistown,  Pennsylvania,  for  copious  notes  of  his  exten- 
sive experience  in  the  analyses  of  steel,  iron,  and  iron  ores,  which 
have  been  freely  employed  in  §  229.  To  Mr.  William  G.  Mixter, 
•chief  assistant  in  the  Sheffield  Laboratory,  for  the  account  of  the 
.gold  and  silver  assay.  To  Professor  Brush,  of  Yale  College,  Pro- 
fessor Collier,  of  Vermont  University,  and  B.  S.  Burton,  Esq.,  of 
Philadelphia,  for  various  important  facts  and  suggestions.  Just 
before  going  to  press,  Dr.  Wolcott  Gibbs  has  communicated  an 
account  of  his  new  method  of  finding  at  once  the  total  correction 
for  temperature,  pressure,  and  moisture  in  absolute  determinations 
of  nitrogen  or  other  gases,  which,  from  its  simplicity,  convenience, 
and  accuracy,  must  prove  of  the  highest  service  in  chemistry.  It 
will  be  found  in  the  Appendix,  p.  838. 

The  additions  which  have  been  made  to  the  methods  of  exam- 
ining ores,  it  is  believed,  adapt  the  work  to  meet  all  the  ordinary 
requirements  of  the  metallurgical  and  mining  student. 

The  editor's  additions  are  distinguished;  in  all  important  cases, 
by  enclosure  in  brackets,  [  ]. 

While  fully  recognizing  the  necessity  of  teaching  the  new 
notation  and  nomenclature  of  chemistry,  the  editor  has  in  this 
book  retained  the  old  system,  because  it  is  identified  with  the 
chemical  literature  of  the  century,  and  cannot  be  speedily  forgot- 
ten by  practical  men.  At  a  time  when  the  most  elementary  text- 
books are  framed  on  the  "  modern"  system,  it  is  important  to  keep 
the  student  exercised  in  the  language  of  the  old  masters  of  the 
science,  which  is  still,  and  must  for  some  time  remain,  a  part  of 
the  vernacular  of  the  physician,  the  apothecary,  the  metallurgist, 
and  the  manufacturer. 

SAMUEL  W.  JOHNSON. 

SHEFFIELD  LABORATORY  OF  YALE  COLLEGE,  Dec.,  1869. 


CONTENTS. 


PAGX 

INTRODUCTION  , ,....,... 1 

PART   I. 


SECTION  I. 

Operations,  §  1 11 

I.  Determination  of  quantity,  §2 , 11 

1.  Weighing,  §  3 11 

a.  The  balance 12 

Accuracy,  §4 12 

Sensibility,  §  5 14 

Testing,  §  6  and  §7 17 

b.  The  weights,  §  8 18 

c.  The  process  of  weighing,  §  9 20 

Rules,  §  10 22 

2.  Measuring,  §  11 24 

a.  The  measuring  of  gases,  §  12 25 

Correct  reading-off,  §  13 27 

Influence  of  temperature,  §  14 28 

Influence  of  pressure,  §  15 29 

Influence  of  moisture,  §  16 29 

b.  The  measuring  of  fluids,  §  17 30 

a.  Measuring  vessels  graduated  to  hold  certain  volumes 

of  fluid. 

aa.  Vessels  serving  to  measure  out  one  definite  volume 
of  fluid. 

1.  Measuring  flasks,  §  18 30 

bb.  Vessels  serving  to  measure  out  different  volumes  of 

fluid. 

2.  The  graduated  cylinder,  §  19 32 

ft.  Measuring  vessels  graduated  to  deliver  certain  volumes 

of  fluid. 

eta.  Vessels  serving  to  measure  out  one  definite  volume 
of  fluid. 


viii  CONTENTS. 

PAGE 

3.  The  graduated  pipette,  §  20 33 

bb.  Vessels  serving  to  measure  out  different  volumes  of 

fluid. 

4.  The  Burette. 

I.  Mohr's  burette,  §  21 36 

II.  Gay-Lussac's  burette,  §  22 40 

III,  Geissler's  burette,  §  23 41 

II.  Preliminary  operations.     Preparation  of  substances  for  the  processes 
of  quantitative  analysis. 

1.  Selection  of  the  sample,  §  24 42 

2.  Mechanical  division,  §  25 43 

3.  Drying,  §  26 46 

Desiccators,  §  27 , 48 

Water-baths,  §  28 49 

Air-baths,  §  29 52 

Parafflne-baths,  §  30 54 

III.  General  procedure  in  quantitative  analysis,  §  32 55 

1.  Weighing  the  substance,  §  33 56 

2.  Estimation  of  water,  §  34 57 

a.  Estimation  of  water  by  loss  of  weight,  §  35 58 

b.  Estimation  of  water  by  direct  weighing,  §  36 60 

3.  Solution  of  substances,  §  37 63 

a.  Direct  solution,  §  38 64 

b.  Decomposition  by  fluxing,  §  39 65 

4.  Conversion  of  the  dissolved  substance  into  a  weighable  form, 

§40 66 

a.  Evaporation,  §  41 66 

Weighing  of  residues,  §  42 72 

b.  Precipitation,  §  43 74 

a.  Separation  of  precipitates  by  decantation,  §  44 75 

/?.  Separation  of  precipitates  by  filtration,  §  45 76 

aa.  Filtering  apparatus  77 

bb.  Rules  to  be  observed  in  the  process  of  filtration, 

§46 79 

cc.  Washing  of  precipitates,  §  47 81 

y.  Separation  of  precipitates  by  decantation  and  filtra- 
tion combined,  §  48 82 

Further  treatment  of  precipitates  preparatory  to  weigh- 
ing, §49 83 

aa.  Drying  of  precipitates,  §  50 84 

bb.  Ignition  of  precipitates,  §  51 85 

First  method,  §  52 88 

Second  method,  §  53 90 

Bunsen's  method  of  rapid  filtration,  §  53,  a 91 

Bunsen's  simplified  exhausting  apparatus,  §  53,  b 97 

Bunsen's  method  of  igniting  precipitates,  §  53,  c 98 

Use  of  asbestos  filters,  §  53,  d 100 

5.  Volumetric  analysis,  §  54 102 


CONTENTS.  IX 


SECTION  II. 

PAGE 

Reagents,  §  55 105 

A.  Reagents  for  gravimetric  analysis  in  the  wet  way. 

I.  Simple  solvents,  §56 105 

II.  Acids  and  halogens. 

a.  Oxygen  acids,  §  57 106 

b.  Hydrogen  acids  and  halogens,  §  58 107 

c.  Sulpho-acids 109 

III.  Bases  and  metals. 

a.  Oxygen  bases  and  metals. 

a.  Alkalies,  and 

ft.  Alkaline  earths,  §  59 109 

y.  Heavy  metals  and  oxides  of  heavy  metals,  §  60 110 

b.  Sulpho-bases Ill 

IV.  Salts. 

a.  Salts  of  the  alkalies,  §  61  Ill 

b.  Salts  of  the  alkali-earth  metals,  §  62 112 

c.  Salts  of  the  heavy  metals,  §  63 113 

B.  Reagents  for  gravimetric  analysis  in  the  dry  way,  §  64  114 

C.  Reagents  for  volumetric  analysis,  §  65 117 

D.  Reagents  for  organic  analysis,  §  66 123 

SECTION  HI. 

Forms  and  combinations  in  which  substances  are  separated  from  each 
other,  or  weighed,  §  67 130 

A.  BASIC  RADICALS. 

FIRST  GROUP. 

1.  Potassium,  §  68 132 

2.  Sodium,  §  69 135 

3.  Ammonium,  §  70 137 

SECOND  GROUP. 

1.  Barium,  §71 138 

2.  Strontium,  §  72 '. 141 

3.  Calcium,  §73 143 

4.  Magnesium,  §  74 146 

THIRD   GROUP. 

1.  Aluminium,  §  75 149 

2.  Chromium,  §76 151 

FOURTH  GROUP. 

1.  Zinc,  §77 153 

2.  Manganese,  §  78 155 


X  CONTENTS. 

PAGE 

3.  Nickel,  §79 159 

4.  Cobalt,  §80 161 

5.  Ferrous  iron ;  and  6.  Ferric  iron,  §  81 164 

FIFTH   GROUP. 

1.  Silver,  §82 167 

2.  Lead,  §83 170 

3.  Mercury  in  mercurous;  and  4.  in  mercuric  compounds,  §  84 174 

5.  Copper,  §85 177 

6.  Bismuth,§86 180 

7.  Cadmium,  §  87. 182 

SIXTH  GROUP. 

1.  Gold,§88 184 

2.  Platinum,  §  89 184 

3.  Antimony,  §  90 185 

4.  Tin  in  stannous;  and  5.  in  stannic  compounds,  §  91  188 

6.  Arsenious  acid;  and  7.  Arsenic  acid,  §  92 190 

B.  ACIDS. 

FIRST  GROUP,  §   93. 

1.  Arsenious  and  arsenic  acids. 

2.  Chromic  acid 193 

3.  Sulphuric  acid 195 

4.  Phosphoric  acid 195 

5    Boracic  acid 200 

6.  Oxalic  acid 200 

7.  Hydrofluoric  acid 200 

8.  Carbonic  acid 201 

9.  Silicic  acid 201 

SECOND   GROUP,    §   94. 

1.  Hydrochloric  acid 203 

2.  Hydrobromic  acid 203 

3.  Hydriodic  acid 204 

4.  Hydrocyanic  acid 205 

5.  Hydrosulphuric  acid 205 

THIRD   GROUP,    §   95. 

1.  Nitric  acid 206 

2.  Chloric  acid 206 

SECTION  IV. 

Determination  of  radicals,  §  96 207 

I.  Determination  of  basic  radicals 210 

FIRST  GROUP. 

1.  Potassium,  §  97 210 

2.  Sodium,  §  98 215 


CONTENTS.  Xl 

PAGE 

3.  Ammonium,  §  99 217 

Supplement  to  first  group,  §  100. 

4.  Lithium 226 

SECOND  GROUP. 

1.  Barium,  §101 227 

2.  Strontium,  §  102 230 

3.  Calcium,  §103 232 

4.  Magnesium,  §  104 237 

THIRD  GROUP. 

1.  Aluminium,  §  105 240 

2.  Chromium,  §  106 1 243 

Supplement  to  third  group,  §  107. 

3.  Titanium 245 

FOURTH  GROUP. 

1.  Zinc,  §108 247 

2.  Manganese,  §  109 251 

3.  Nickel,  §  110 258 

4.  Cobalt,  §  111  262 

5.  Ferrous  iron,  §  112 265 

6.  Ferric  iron,  §  113 275 

Supplement  to  fourth  group,  §  114 

7.  Uranium 281 

FIFTH  GROUP. 

1.  Silver,  §115 283 

2.  Lead,  §116 297 

3.  Mercury  in  mercurous  compounds,  §  117 304 

4.  Mercury  in  mercuroic  compounds,  §  118 306 

5.  Copper,  §  119 31 1 

6.  Bismuth,  §  120 318 

7.  Cadmium,  §121 323 

Supplement  to  fifth  group,  §  122. 

8.  Palladium 325 

SIXTH  GROUP. 

1.  Gold,  §  123 326 

2.  Platinum,  §124 329 

3.  Antimony,  §  125 831 

4.  Tin  in  stannous;  and  5.  in  stannic  compounds,  §  126 338 

6.  Arsenious  acid ;  and  7.  Arsenic  acid,  §  127 344 

Supplement  to  sixth  group,  §  128. 

8.  Molybdic  acid 353 

II.  Estimation  of  the  acids. 

FIRST  GROUP. 

First  Division. 

1.  Arsenious  and  arsenic  acids,  §  129 355 


xii  CONTENTS. 

PAGE 

2.  Chromic  acid,  §  130 355 

Supplement,  §  131. 

1.  Selenious  acid 361 

2.  Sulphurous  acid .  363 

3.  Thiosulplmric  acid 364 

4.  lodic  acid 364 

5.  Nitrous  acid 365 

Second  Division. 

Sulphuric  acid,  §  132 366 

Supplement,  §  133. 

Hydrofluosilicic  acid 372 

Third  Division. 

1.  Phosphoric  acid. 

I.  Determination,  §  134 373 

II.  Separation  from  the  bases,  §  135 383 

2.  Boric  acid,  §  136 389 

3.  Oxalic  acid,  §  137 394 

4.  Hydrofluoric  acid,  §  138 396 

Fourth  Division. 

1.  Carbonic  acid,  §  139 403 

2.  Silicic  acid,  §  140 419 

SECOND  GROUP. 

1.  Chlorine  (Hydrochloric  acid),  §  141 428 

Supplement:  free  chlorine,  §  142 434 

2.  Bromine  (Hydrobromic  acid),  §  143 436 

Supplement:  free  bromine,  §  144 439 

3.  Iodine  (Hydriodic  acid),  §  145 439 

Supplement :  free  iodine,  §  146 44  B 

4.  Cyanogen  (Hydrocyanic  acid),  §  147 449 

5.  Sulphur  (Hydrosulphuric  acid),  §  148 457 

THIRD   GROUP. 

1.  Nitric  acid,  §  149 469 

2.  Chloric  acid,  §  150. 476 


SECTION  V. 
Separation  of  bodies,  §  151 478 

I.    SEPARATION   OF   BASIC   RADICALS  FROM  EACH   OTHER. 
FIRST   GROUP. 

Separation  of  the  alkalies  from  each  other,  §  152 481 

SECOND   GROUP. 

I.  Separation  of  the  basic  radicals  of  the  second  group  from  those  of  the 

first,  §  153 ; 488 


CONTENTS. 

PAGE 

II.  Separation  of  the  basic  radicals  of  the  second  group  from  eacn  other, 

§  154 .„    493 

THIRD   GROUP. 

I.  Separation  of  aluminium  and  chromium  from  the  alkalies,  §  155 499 

II.  Separation  of  aluminium  and  chromium  from  the  alkali-earth  metals, 

§  156 500 

III.  Separation  of  aluminium  and  chromium  from  each  other,  §  157 506 

FOURTH  GROUP. 

I.  Separation  of  the  metals  of  the  fourth  group  from  the  alkalies,  §  158. .     507 
II.  Separation  of  the  metals  of  the  fourth  group  from  those  of  the  second, 

§159 509 

III.  Separation  of  the  metals  of  the  fourth  group  from  those  of  the  third 

and  from  each  other,  §  160 512 

IV.  Separation  of  iron,  aluminium,  manganese,  calcium,  magnesium,  potas- 

sium, and  sodium,  §  161 529 

Separation  of  uranium  from  the  metals  of  groups  I. — IV 532 

FIFTH  GROUP. 

I.  Separation  of  the  metals  of  the  fifth  group  from  those  of  the  preced- 
ing four  groups,  §  162 536 

II.  Separation  of  the  metals  of  the  fifth  group  from  each  other,  §  163 543 

SIXTH   GROUP. 

I.  Separation  of  the  metals  of  the  sixth  group  from  Lhose  of  the  first  five 

groups,  §  164 554 

II.  Separation  of  the  metals  of  the  sixth  group  from  each  other,  §  165. . .     569 


IL    SEPARATION  OF  ACIDS  FROM  EACH  OTHER. 
FIRST   GROUP. 

Separation  of  the  acids  of  the  first  group  from  each  other,  §  166 580 

SECOND  GROUP. 

I.  Separation  of  the  acids  of  the  second  group  from  those  of  the  first, 

§167 588 

Supplement. — Analysis  of  compounds  containing  sulphides  of  the 

alkali  metals,  carbonates,  sulphates,  and  thiosulphates,  §  168 591 

II.  Separation  of  the  acids  of  the  second  group  from  each  other,  §  169. . .     532 

THIRD   GROUP. 

I.  Separation  of  the  acids  of  the  third  group  from  those  of  the  two  first 

groups,  §  170 602 

II.  Separation  of  the  acids  of  the  third  group  from  each  other 603 


CONTENTS. 


SECTION  VI. 

PAGE 

Ultimate  analysis  of  organic  bodies,  §  171 604 

I.  Qualitative,  §  172 606 

II.  Quantitative,  §  173 609 

A.  Substances  consisting  of  carbon  and  hydrogen,  or  of  carbon,  hydro- 

gen, and  oxygen. 

a.  Solid  bodies. 

Combustion  with  oxide  of  copper,  §  174 610 

Completion  of  the  combustion  by  oxygen  gas,  §  176 620 

Combustion  with  lead  chromate  (and  potassium  dichromate) 

§  177 620 

Combustion  with  oxide  of  copper  and  oxygen  gas,  §  178 621 

Volatile  bodies,  or  bodies  undergoing  alteration  at  100°,  §  179.  627 

b.  Liquid  bodies. 

a.  Volatile  bodies,  §  180 627 

ft.  Non-volatile  bodies,  §  181 630 

Supplement  to  A. — Modified  apparatus  for  absorption  of  carbonic 
acid,  §  182 631 

B.  Substances  consisting  of  carbon,  hydrogen,  oxygen,  and  nitrogen. 

a.  Estimation  of  carbon  and  hydrogen,  §  183 633 

b.  Estimation  of  nitrogen. 

a.  From  the  volume,  §  184 635 

/?.  By  conversion  into  ammonia,  after  Varrentrapp  and  Will, 

§185 644 

C.  Analysis  of  bodies  containing  sulphur,  §  186 649 

D.  Estimation  of  phosphorus  in  organic  bodies,  §  187. 660 

E.  Analysis  of  substances  containing  chlorine,   bromine,   or  iodine, 

§188 661 

F.  Analysis  of  organic  substances  containing  inorganic  bodies,  §  189..     664 


PART   II. 

SPJCCI^JL, 


1.  Analysis  of  fresh  water,  §  190  .....................................    669 

2.  Acidimetry. 

A.  Estimation  by  specific  gravity,  §  191  ..........................    675 

B.  Determination  of  the  acid  by  saturation  with  an  alkaline  fluid  of 

known  strength,  §  192  ..................   .................     675 

Kiefer's  modification  of  the  process,  §  193  ................      689 

3.  Alkalimetry. 

A.  Estimation  of  potassa,  soda,  or  ammonia,  from  the  density  of 

their  solutions,  §  194  ......................................     691 

B.  Estimation  of  the  amount  of  caustic  and  carbonated  alkali  in 

commercial  alkalies  .................  691 


CONTENTS.  XV 

/ 

PAGE 

Method  of  Descroizilles  and  Gay-Lussac,  §  195. . . 692 

Modification  by  Mobr,  §  196 694 

C.  Estimation  of  caustic  alkali  in  the  presence  of  carbonates,  §  197.  695 

D.  Estimation  of  sodium  carbonate  in  presence  of  potassium  car- 

bonate   696 

4.  Estimation  of  alkali-earth  metals  by  the  alkalimetric  method,  §  198. . .  697 

5.  Chlorimetry,  §  199. 698 

Preparation  of  the  solution  of  chloride  of  lime 699 

A.  Penot's  method,  §  200 699 

B.  Otto's  method,  §  201 701 

Modification 703 

C.  Bunsen's  method 703 

6.  Valuation  of  manganese,  §  202 704 

I.  Drying  the  sample 704 

II.  Determination  of  the  manganese  dioxide,  §  203 705 

A.  Fresenius  and  Will's  method 705 

B.  Bunsen's  method 709 

C.  Method  by  means  of  iron 709 

III.  Estimation  of  moisture  in  manganese,  §  204 710 

IV.  Estimation  of  the  amount  of  hydrochloric  acid  required  for  the 

complete  decomposition  of  a  manganese,  §  205 711 

7.  Analysis  of  common  salt,  §  206 711 

8.  Analysis  of  gunpowder,  §  207 713 

9.  Analysis  of  silicates  and  siliceous  rocks,  §  208 714 

10.  Separation  of  silicates  decomposable  from  those  undecomposable  by 

acids,  §  209 719 

11.  Analysis  of  limestones,  dolomites,  marls,  &c 720 

A.  Complete  analysis,  §  210 721 

B.  Volumetric  determination  of  calcium  carbonate,  &c.,  §  211 726 

12.  Assay  of  copper  ores,  §  212 728 

13.  Assay  of  lead  ores,  §  213 730 

14.  Determination  of  nickel  and  cobalt  in  ores,  &c.,  §  214 731 

15.  Assay  of  zinc  ores,  §  215 737 

16.  Partial  analysis  of  iron  ores,  §  216 740 

17.  Complete  analysis  of  iron  ores,  §  217 753 

18.  Analysis  of  pig  iron,  steel,  and  wrought  iron,  §  218 758 

I.  Pigiron 758 

II.  Steel  and  wrought  iron 765 

19.  Analysis  of  coal  and  peat,  §  219 765 

20.  Analysis  of  commercial  fertilizers,  §  220 767 

21.  Analysis  of  atmospheric  air,  §  221 772 

A.  Determination  of  water  and  carbonic  acid,  §  222 , 772 

B.  Determination  of  oxygen  and  nitrogen,  §  223 779 

22.  Detection  and  estimation  of  arsenic  in  organic  matter,  224 781 


XVl  CONTENTS. 


PAET  III. 

PAGE 

Exercises  for  practice 789 


APPENDIX. 

Analytical  experiments 809 

Calculation  of  analyses 834 

I.  Calculation  of  the  constituent  sought  from  the  compound  produced, 

and  exhibition  of  the  results  in  per-cents 834 

1.  When  the  substance  sought  has  been  separated  in  the  free  state. 

a.  Solid  bodies,  liquids,  or  gases,  which  have  been  determined 

by  weight 834 

b.  Gases  which  have  been  measured 835 

2.  When  the  substance  sought  has  been  separated  in  combination 

with  another 839 

3.  Calculation  of  indirect  analyses 841 

Supplement  to  I. — Remarks  on  loss  and  excess,  and  on  taking  the 

average 842 

II.  Deduction  of  formulae 844 

Tables  for  the  calculation  of  analyses 849 — 872 

I.  Atomic  weights  of  the  elements 849 

II.  Composition  of  basic  and  acid  oxides 849 

III.  Reduction  of  compounds  found  to  constituents  sought  by  simple 

multiplication  or  division 854 

IV.  Amount  of  constituent  sought  for  each  number  of  compound  found  856 
V.  Specific  gravity  and  absolute  weight  of  several  gases 872 

VI.  Comparison  of  degrees  of  mercurial  thermometer  with  those  of  air 

thermometer. .  872 


INTRODUCTION. 


As  we  have  already  seen  in  the  "  Manual  of  Qualitative  Analy- 
sis,"— to  which  the  present  work  may  be  regarded  as  the  sequel, 
—Chemical  Analysis  comprises  two  branches,  viz.  :  qualitative 
analysis  and  quantitative  analysis,  the  object  of  the  former  being 
to  ascertain  the  nature,  that  of  the  latter  to  determine  the  amount, 
of  the  several  component  parts  of  any  compound. 

By  QUALITATIVE  ANALYSIS  we  convert  the  unknown  constituents 
of  a  body  into  certain  known  forms  and  combinations  ;  and  we  are 
thus  enabled  to  draw  correct  inferences  respecting  the  nature  of 
these  unknown  constituents.  Quantitative  analysis  attains  its  ob- 
ject, according  to  circumstances,  often  by  very  different  ways  ;  the 
two  methods  most  widely  differing  from  each  other,  are  analysis 
by  weight,  or  gravimetric  analysis,  and  analysis  lyy  measure,  or 
volumetric  analysis. 

GRAVIMETRIC  ANALYSIS  has  for  its  object  to  convert  the  known 
constituents  orf  a  substance  into  forms  or  combinations  which  will 
admit  of  the  most  exact  determination  of  their  weight,  and  of 
which,  moreover,  the  composition  is  accurately  known.  These  new 
forms  or  combinations  may  be  either  educts  from  the  analyzed  sub- 
stance, or  they  may  be  products.  In  the  former  case  the  ascer- 
tained weight  of  the  eliminated  substance  is  the  direct  expression 
of  the  amount  in  which  it  existed  in  the  compound  under  exami- 
nation ;  whilst  in  the  latter  case,  that  is,  when  we  have  to  deal  with 
products,  the  quantity  in  which  the  eliminated  constituent  was  ori- 
ginally present  in  the  analyzed  compound,  has  to  be  deduced  by 
calculation  from  the  quantity  in  which  it  exists  in  its  new  com- 
bination. 

The  following  example  will  serve  to  illustrate  these  points : — 
Suppose  we  wish  to  determine  the  quantity  of  mercury  contained 


2  INO/RODUCTION. 

in  the  chloride  of  that  metal ;  now,  we  may  do  this,  either  by  pre- 
cipitating the  metallic  mercury  from  the  solution  of  the  chloride, 
say  by  means  of  stannous  chloride ;  or  we  may  attain  our  object  by 
precipitating  the  solution  by  sulphuretted  hydrogen,  and  weighing 
the  precipitated  mercuric  sulphide.  100  parts  of  mercuric  chloride 
consist  of  73*82  of  mercury  and  26*18  of  chlorine ;  consequently, 
if  the  process  is  conducted  with  absolute  accuracy,  the  precipitation 
of  mercury  in  100  parts  of  mercuric  chloride  by  stannous  chloride 
will  yield  73*82  parts  of  metallic  mercury.  With  equally  exact 
manipulation  the  other  method  yields  85*634  parts  of  mercuric 
sulphide. 

Now,  in  the  former  case  we  find  the  number  73*82  directly ;  in 
the  latter  case  we  have  to  deduce  it  by  calculation  : — (100  parts  of 
mercuric  sulphide  contain  86*207  parts  of  mercury ;  how  much 
mercury  do  85*634  parts  contain  ?) 

100  :  85*634::  86*207  :  x  —  x  =  73'82. 

As  already  hinted,  it  is  absolutely  indispensable  that  the  forms 
into  which  bodies  are  converted  for  the  purpose  of  estimation  by 
weight  should  fulfil  two  conditions  :  first,  they  must  be  capable  of 
being  weighed  exactly;  secondly,  they  must  be  ofs known  composi- 
tion,— for  it  is  quite  obvious,  on  the  one  hand,  that  accurate  quan- 
titative analysis  must  be  altogether  impossible  if  the  substance  the 
quantity  of  which  it  is  intended  to  ascertain,  does  not  admit  of 
correct  weighing;  and  on  the  other  hand,  it  is  equally  evident  that 
if  we  do  not  know  the  exact  composition  of  a  new  product,  we  lack 
the  necessary  basis  of  our  calculation. 

YOLUMETRIC  ANALYSIS  is  based  upon  a  very  different  principle 
from  that  of  gravimetric  analysis ;  viz.,  it  effects  the  quantitative 
determination  of  a  body,  by  converting  it  from  a  certain  definite 
state  to  another  equally  definite  state,  by  means  of  a  fluid  of  accu- 
rately known  power  of  action,  and  under  circumstances  which  per- 
mit the  analyst  to  mark  with  rigorous  precision  the  exact  point 
when  the  conversion  is  accomplished.  The  following  example  will 
serve  to  illustrate  the  principle  of  this  method : — Potassium  per- 
manganate added  to  a  solution  of  ferrous  sulphate,  acidified  with 
sulphuric  acid,  immediately  converts  the  ferrous  sulphate  into  fer- 
ric sulphate ;  the  permanganic  acid,  which  is  characterized  by  its 
intense  color,  yielding  np  oxygen  and  forming  with  the  free  sul- 


INTRODUCTION.  3 

phuric  acid  present  colorless  manganous  sulphate.  If,  therefore, 
to  an  acidified  fluid  containing  a  ferrous  salt  we  add,  drop  by  drop, 
a  solution  of  potassium  permanganate,  its  red  color  continues  for 
some  time  to  disappear  upon  stirring ;  but  at  last  a  point  is  reached 
when  the  coloration  imparted  to  the  fluid  by  the  last  drop  added 
remains ;  this  point  marks  the  termination  of  the  conversion  of  the 
ferrous  salt  into  a  ferric  salt. 

If  now  we  convert  a  known  weight  of  iron  into  a  ferrous  sul- 
phate by  dissolving  it  in  dilute  sulphuric  acid,  and  ascertain  by 
suitable  measuring  apparatus  the  volume  of  a  solution  of  potassium 
permanganate  required  to  convert  the  ferrous  sulphate  to  ferric 
sulphate,  we  can  by  means  of  this  permanganate  solution  determine 
unknown  quantities  of  ferrous  iron  in  a  solution.  This  is  accom- 
plished by  adding  the  permanganate  solution  until  the  above  de- 
scribed reaction  is  completed,  and  noting  the  volume  used.  The 
amount  of  iron  present  can  now  be  calculated  by  comparing  the 
volume  used  with  that  used  when  a  known  quantity  of  iron  was 
present,  as  the  weight  of  iron  must  in  both  cases  be  proportional  to 
volume  of  permanganate  used. 

To  this  brief  intimation  of  the  general  purport  and  object  of 
quantitative  analysis,  and  the  general  mode  of  proceeding  in  ana- 
lytical researches',  I  have  to  add  that  certain  qualifications  are  essen- 
tial to  those  who  would  devote  themselves  successfully  to  the 
pursuit  of  this  branch.  These  qualifications  are,  1,  theoretical 
knowledge ;  2,  skill  in  manipulation ;  and  3,  strict  conscientious- 
ness. 

The  preliminary  knowledge  required  consists  in  an  acquaintance 
with  qualitative  analysis,  the  stoichiornetric  laws,  and  simple  arith- 
metic. Thus  prepared,  we  shall  understand  the  method  by  which 
bodies  are  separated  and  determined,  and  we  shall  be  in  a  position 
to  perform  our  calculations,  by  which,  on  the  one  hand,  the  formu- 
lae of  compounds  are  deduced  from  the  analytical  results,  and,  on 
the  other  hand,  the  correctness  of  the  adopted  methods  is  tested, 
and  the  results  obtained  are  controlled.  To  this  knowledge  must 
be  joined  the  ability  of  performing  the  necessary  practical  opera- 
tions. This  axiom  generally  holds  good  for  all  applied  sciences, 
but  if  it  is  true  of  one  more  than  another,  quantitative  analysis  is 
that  one.  The  most  extensive  and  solid  theoretical  acquirements 
will  not  enable  us,  for  instance,  to  determine  the  amount  of  com- 
mon salt  present  in  a  solution,  if  we  are  without  the  requisite  dex- 


4  INTRODUCTION. 

teritj  to  transfer  a  fluid  from  one  vessel  to  another  without  the 
smallest  loss  by  spirting,  running  down  the  side,  &c.  The  various 
•operations  of  quantitative  analysis  demand  great  aptitude  and  man- 
ual skill,  which  can  be  acquired  only  by  practice.  But  even  the 
possession  of  the  greatest  practical  skill  in  manipulation,  joined  to 
a  thorough  theoretical  knowledge,  will  still  prove  insufficient  to 
insure  a  successful  pursuit  of  quantitative  researches,  unless  also 
combined  with  a  sincere  love  of  truth  and  a  firm  determination 
to  accept  none  but  thoroughly  confirmed  results. 

Every  one  who  has  been  engaged  in  quantitative  analysis  knows 
that  cases  will  sometimes  occur,  especially  when  commencing  the 
study,  in  which  doubts  may  be  entertained  as  to  whether  the  result 
will  turn  out  correct,  or  in  which  even  the  operator  is  positively 
convinced  that  it  cannot  be  quite  correct.  Thus,  for  instance,  a 
small  portion  of  the  substance  under  investigation  may  be  spilled ; 
or  some  of  it  lost  by  decrepitation ;  or  the  analyst  may  have  reason 
to  doubt  the  accuracy  of  his  weighing ;  or  it  may  happen  that  two 
analyses  of  the  same  substance  do  not  exactly  agree.  In  all  such 
cases  it  is  indispensable  that  the  operator  should  be  conscientious 
enough  to  repeat  the  whole  process  over  again.  He  who  is  not 
possessed  of  this  self-command — who  shirks  trouble  where  truth  is 
at  stake — who  would  be  satisfied  with  mere  assumptions  and  guess- 
work, where  the  attainment  of  positive  certainty  is  the  object,  must 
be  pronounced  just  as  deficient  in  the  necessary  qualifications  for 
quantitative  analytical  researches  as  he  who  is  wanting  in  knowl- 
edge or  skill.  He,  therefore,  who  cannot  fully  trust  his  work— 
r  who  cannot  swear  to  the  correctness  of  his  results,  may  indeed  oc- 
cupy himself  with  quantitative  analysis  by  way  of  practice,  but  he 
ought  on  no  account  to  publish  or  use  his  results  as  if  they  were 
positive,  since  such  proceeding  could  not  conduce  to  his  own  ad- 
vantage, and  would  certainly  be  mischievous  as  regards  the  science. 

The  domain  of  quantitative  analysis  may  be  said  to  extend  over 
all  matter — that  is,  in  other  words,  anything  corporeal  may  become 
the  object  of  quantitative  investigation.  The  present  work,  how- 
ever, is  intended  to  embrace  only  the  substances  used  in  pharmacy, 
arts,  trades,  and  agriculture. 

Quantitative  analysis  may  be  subdivided  into  two  branches,  viz., 
analysis  of  mixtures,  and  analysis  of  chemical  compounds.  This 
division  may  appear  at  first  sight  of  very  small  moment,  yet  it  is 
necessary  that  we  should  establish  and  maintain  it,  if  we  would 


INTRODUCTION.  5 

form  a  clear  conception  of  the  value  and  utility  of  quantitative 
research.  The  quantitative  analysis  of  mixtures,  too,  has  not  the 
same  aim  as  that  of  chemical  compounds ;  and  the  method  applied 
to  secure  the  correctness  of  the  results  in  the  former  case  is  dif- 
ferent from  that  adopted  in  the  latter.  The  quantitative  analysis 
of  chemical  compounds  also  rather  suttserves  the  purposes  of  the 
science,  whilst  that  of  mixtures  belongs  to  the  practical  purposes  of 
life.  If,  for  instance,  I  analyze  the  salt  of  an  acid,  the  result  of 
the  analysis  will  give  me  the  constitution  of  that  acid,  its  com- 
bining proportion,  saturating  capacity,  &c. ;  or,  in  other  words,  the 
results  obtained  will  enable  me  to  answer  a  series  of  questions  of 
which  the  solution  is  important  for  the  theory  of  chemical  science : 
but  if,  on  the  other  hand,  I  analyze  gunpowder,  alloys,  medicinal 
mixtures,  ashes  of  plants,  &c.,  &c.,  I  have  a  very  different  object 
in  view ;  I  do  not  want  in  such  cases  to  apply  the  results  which  I 
may  obtain  to  the  solution  of  any  theoretical  question  in  chemistry, 
but  I  want  to  render  a  practical  service  either  to  the  arts  and 
industries,  or  to  some  other  science.  If  in  the  analysis  of  a  chemi- 
cal compound  I  wish  to  control  the  results  obtained,  I  may  do  this 
in  most  cases  by  means  of  calculations  based  on  stoi'chiometric 
data,  but  in  the  case  of  a  mixture  a  second  analysis  is  necessary  to 
confirm  the  correctness  of  the  results  afforded  by  the  first. 

The  preceding  remarks  clearly  show  the  immense  importance 
of  quantitative  analysis.  It  may,  indeed,  be  averred  that  chemistry 
owes  to  this  branch  its  elevation  to  the  rank  of  a  science,  since 
quantitative  researches  have  led  us  to  discover  and  determine  the 
laws  which  govern  the  combinations  and  transpositions  of  the  ele- 
ments. Stoichiometry  is  entirely  based  upon  the  results  of  quan- 
titative investigations ;  all  rational  views  respecting  the  constitution 
of  compounds  rest  upon  them  as  the  only  safe  and  solid  basis. 

Quantitative  analysis,  therefore,  forms  the  strongest  and  most 
powerful  lever  for  chemistry  as  a  science,  and  not  less  so  for  chemis- 
try in  its  applications  to  the  practical  purposes  of  life,  to  trades,  arts, 
manufactures,  and  likewise  in  its  application  to  other  sciences.  It 
teaches  the  mineralogist  the  true  nature  of  minerals,  and  suggests 
to  him  principles  and  rules  for  their  recognition  and  classification. 
It  is  an  indispensable  auxiliary  to  the  physiologist ;  and  agriculture 
has  already  derived  much  benefit  from  it ;  but  far  greater  benefits 
may  be  predicted.  We  need  not  expatiate  here  upon  the  advan- 
tages which  medicine,  pharmacy,  and  every  branch  of  industry 


6  INTRODUCTION. 

derive,  either  directly  or  indirectly,  from  the  practical  application 
of  its  results.  On  the  other  hand,  the  benefit  thus  bestowed  by 
quantitative  analysis  upon  the  various  sciences,  arts,  etc.,  has  been 
in  a  measure  reciprocated  by  some  of  them.  Thus  whilst  stoichio- 
metry  owes  its  establishment  to  quantitative  analysis,  the  stoichio- 
metric  laws  afford  us  the  means  of  controlling  the  results  of  our 
analyses  so  accurately  as  to  justify  the  reliance  which  we  now  gen- 
erally place  on  them.  Again,  whilst  quantitative  analysis  has 
advanced  the  progress  of  arts  and  industry,  our  manufacturers  in 
return  supply  us  with  the  most  perfect  platinum,  glass,  and  por- 
celain vessels,  and  with  articles  of  india-rubber,  without  which  it 
would  be  next  to  impossible  to  conduct  our  analytical  operations 
with  the  minuteness  and  accuracy  which  we  have  now  attained. 

Although  the  aid  which  quantitative  analysis  thus  derives 
from  stoichiometry,  and  the  arts  and  manufactures,  greatly 
facilitates  its  practice,  and  although  many  determinations  are  con- 
siderably abbreviated  by  volumetric  analysis,  it  must  be  admitted, 
notwithstanding,  that  the  pursuit  of  this  branch  of  chemistry 
requires  considerable  expenditure  of  time.  This  remark  applies 
especially  to  those  who  are  commencing  the  study,  for  they  must 
not  allow  their  attention  to  be  divided  upon  many  things  at  one 
time,  otherwise  the  accuracy  of  their  results  will  be  more  or  less 
injured.  I  would  therefore  advise  every  one  desirous  of  becoming 
an  analytical  chemist  to  arm  himself  with  a  considerable  share  of 
patience,  reminding  him  that  it  is  not  at  one  bound,  but  gradually, 
and  step  by  step,  that  the  student  may  hope  to  attain  the  neces- 
sary certainty  in  his  work,  the  indispensable  self -reliance  which 
can  alone  be  founded  on  one's  own  results.  However  mechanical, 
protracted,  and  tedious  the  operations  of  quantitative  analysis  may 
appear  to  be,  the  attainment  of  accuracy  will  amply  compensate 
for  the  time  and  labor  bestowed  upon  them ;  whilst,  on  the  other 
hand,  nothing  can  be  more  disagreeable  than  to  find,  after  a  long 
and  laborious  process,  that  our  results  are  incorrect  or  uncertain. 
Let  him,  therefore,  who  would  render  the  study  of  quantitative 
analysis  agreeable  to  himself,  from  the  very  outset  endeavor,  by 
strict,  nay,  scrupulous  adherence  to  the  conditions  laid  down,  to 
attain  correct  results,  at  any  sacrifice  of  time.  1  scarcely  know  a 
better  and  more  immediate  reward  of  labor  than  that  which  springs 
from  the  attainment  of  accurate  results  and  perfectly  correspond- 
ing analyses.  The  satisfaction  enjoyed  at  the  success  of  our  efforts 


INTRODUCTION.  7 

is  surely  in  itself  a  sufficient  motive  for  the  necessary  expenditure 
of  time  and  labor,  even  without  looking  to  the  practical  benefits 
which  we  may  derive  from  our  operations. 

The  following  are  the  substances  treated  of  in  this  work : — 

I.  METALLOIDS,  or  NON  -METALLIC  ELEMENTS. 

Oxygen,  Hydrogen,  Sulphur,  [Selenium,]  Phosphorus,  Chlo- 
rine, Iodine,  Bromine,  Fluorine,  Nitrogen,  Boron,  Silicon,  Car- 
bon. 

II.  METALS. 

Potassium,  Sodium,  [Lithium,']  Barium,  Strontium,  Calcium, 
Magnesium,  Aluminium,  Chromium,  [Titanium,]  Zinc,  Manga- 
nese, Nickel,  Cobalt,  Iron,  [Uranium,']  Silver,  Mercury,  Lead, 
Copper,  Bismuth,  Cadmium,  [Palladium,']  Gold,  Platinum,  Tin, 
Antimony,  Arsenic,  [Molybdenum]. 

(The  elements  enclosed  within  brackets  are  considered  in  sup- 
plementary paragraphs,  and  more  briefly  than  the  rest.) 


I  have  divided  my  subject  into  three  parts.  In  the  first,  I  treat 
of  quantitative  analysis  generally ;  describing  the  execution  of  anal- 
ysis. In  the  second,  I  give  a  detailed  description  of  several  special 
analytical  processes.  And  in  the  third,  a  number  of  carefully  se- 
lected examples,  which  may  serve  as  exercises  for  the  groundwork 
of  the  study  of  quantitative  analysis. 

The  following  table  will  afford  the  reader  a  clear  and  definite 
notion  of  the  contents  of  the  whole  work : — 

I.  GENERAL  PART. 

1.  Operations. 

2.  Reagents. 

3.  Forms  and  combinations  in  which  bodies  are  separated  from 
others,  or  in  which  their  weight  is  determined. 

4.  Determination  of  bodies  in  simple  compounds. 

5.  Separation  of  bodies. 

6.  Organic  elementary  analysis. 


8  INTRODUCTION. 

II.  SPECIAL  PAET. 

1.  Analysis  of  waters. 

2.  Analysis  of  such  minerals  and  technical  products  as  are  most 
frequently  brought  under  the  notice  of  the  chemist ;   including 
methods  for  ascertaining  their  commercial  value. 

3.  Analysis  of  atmospheric  air. 

III.  EXERCISES  FOR  PRACTICE. 

APPENDIX. 

1.  Analytical  experiments. 

2.  Calculation  of  analyses. 

3.  Tables  for  calculation. 


TP.AJRT    I. 


GENERAL    PART, 


THE    EXECUTION    OF   ANALYSIS. 


SECTION  I. 
OPERATIONS. 

§  1. 

MOST  of  the  operations  performed  in  quantitative  research  are  the 
same  as  in  qualitative  analysis,  and  have  been  accordingly  described 
in  my  work  on  that  branch  of  analytical  science.  With  respect  to 
such  operations  I  shall,  therefore,  confine  myself  here  to  pointing 
out  any  modifications  they  may  require  to  adapt  them  for  applica- 
tion in  the  quantitative  branch  ;  but  I  shall,  of  course,  give  a  full 
description  of  such  as  are  resorted  to  exclusively  in  quantitative 
investigations.  Operations  forming  merely  part  of  certain  speci- 
fic processes  will  be  found  described  in  the  proper  place,  under  the 
head  of  such  processes. 

I.  DETERMINATION  OF  QUANTITY. 

§  2. 

The  quantity  of  solids  is  usually  determined  by  weight  /  the 
quantity  of  gases  and  fluids,  in  many  cases  by  measure  •  upon  the 
care  and  accuracy  with  which  these  operations  are  performed,  de- 
pends the  value  of  all  our  results  ;  I  shall  therefore  dwell  minutely 
upon  them. 

§O 
O. 

1.  WEIGHING. 

To  enable  us  to  determine  with  precision  the  correct  weight  of 
a  substance,  it  is  indispensable  that  we  should  possess,  1st,  a  good 
BALANCE,  and  2d.  accurate  WEIGHTS. 


12  OPERATIONS. 

a.  THE  BALANCE. 

Fig.  1  represents  a  form  of  balance  well  adapted  for  analytical 
purposes.  There  are  several  points  respecting  the  construction 
and  properties  of  a  good  balance,  which  it  is  absolutely  necessary  for 
every  chemist  to  understand.  The  usefulness  of  this  instrument 
depends  upon  two  points  :  1st,  its  accuracy r,  and  2d,  its  sensibility 
or  delicacy. 

§4- 

The  ACCURACY  of  a  balance  depends  upon  the  following  condi- 
tions : — 

a.  The  fulcrum  or  the  point  on  which  the  beam  rests  must  lie 
above  the  centre  of  gravity  of  the  balance. 


Fig.  1. 

This  is  in  fact  a  condition  essential  to  every  balance.  If  the 
fulcrum  were  placed  in  the  centre  of  gravity  of  the  balance,  the 
beam  would  not  oscillate,  but  remain  in  any  position  in  which  it  is 
placed,  assuming  the  scales  to  be  equally  loaded.  If  the  fulcrum 
be  placed  below  the  centre  of  gravity,  the  balance  will  be  overset 
by  the  slightest  impulse. 

When  the  fulcrum  is  above  the  centre  of  gravity  the  balance 
represents  a  pendulum,  the  length  of  which  is  equal  to  that  of  the 
line  uniting  the  fulcrum  with  the  centre  of  gravity,  and  this  line 
forms  right  angles  with  the  beam,  in  whatever  position  the  latter 
may  be  placed.  Now  if  we  impart  an  impetus  to  a  ball  suspended 
by  a  thread,  the  ball,  after  having  terminated  its  vibrations,  will 


WEIGHING.  13 

invariably  rest  in  its  original  perpendicular  position  under  the 
point»of  suspension.  It  is  the  same  with  a  properly  adjusted  bal- 
ance— impart  an  impetus  to  it,  and  it  will  oscillate  for  some  time, 
but  it  will  invariably  return  to  its  original  position  ;  in  other 
words,  its  centre  of  gravity  will  finally  fall  back  into  its  perpen- 
dicular position  under  the  fulcrum,  and  the  beam  must  consequently 
reassume  the  horizontal  position. 

But  to  judge  correctly  of  the  force  with  which  this  is  accom- 
plished, it  must  be  borne  in  mind  that  a  balance  is  not  a  simple 
pendulum,  but  a  compound  one,  i.  e.,  a  pendulum  in  which  not 
one,  but  many  material  points  move  round  the  turning  point.  The 
inert  mass  to  be  moved  is  accordingly  equal  to  the  sum  of  these 
ppints,  and  the  moving  force  is  equal  to  the  excess  of  the  material 
points  below,  over  those  above  the  fulcrum. 

ft.  The  points  of  suspension  of  the  scales  must  ~be  on  an  exact 
level  with  the  fulcrum.  If  the  fulcrum  be  placed  below  the  line 
joining  the  points  of  suspension,  increased  loading  of  the  scales 
will  continually  tend  to  raise  the  centre  of  gravity  of  the  whole 
svstem,  so  as  to  bring  it  nearer  and  nearer  the  fulcrum  ;  the  weight 
which  presses  upon  the  scales  combining  in  the  relatively  high- 
placed  points  of  suspension  ;  at  last,  when  the  scales  have  been 
loaded  to  a  certain  degree,  the  centre  of  gravity  will  shift  alto- 
gether to  the  fulcrum,  and  the  balance  will  consequently  cease  to 
vibrate — any  further  addition  of  weight  will  finally  overset  the 
beam  by  placing  the  centre  of  gravity  above  the  fulcrum.  If,  on 
the  other  hand,  the  fulcrum  be  placed  above  the  line  joining  the 
points  of  suspension,  the  centre  of  gravity  will  become  more  and 
more  depressed  in  proportion  as  the  loading  of  the  scales  is  in- 
creased ;  the  line  of  the  pendulum  will  consequently  be  length- 
ened, and  a  greater  force  will  be  required  to  produce  an  equal 
turn ;  in  other  words,  the  balance  will  grow  less  sensitive  the 
greater  the  load.  But  when  the  three  edges  are  in  one  plane,  in- 
creased loading  of  the  scales  will,  indeed,  continually  tend  to  raise 
the  centre  of  gravity  towards  the  fulcrum,  but  the  former  can  in 
this  case  never  entirely  reach  the  latter,  and  consequently  the  bal- 
ance will  never  altogether  cease  to  vibrate  upon  the  further  addi- 
tion of  weight,  nor  will  its  sensibility  be  lessened ;  on  the  contrary 
— speaking  theoretically — a  greater  degree  of  sensibility  is  im- 
parted to  it.  This  increase  of  sensibility  is,  however,  compensated 
for  by  other  circumstancas.  (See  §  5.) 


14  OPERATIONS. 

y.  The  beam  must  be  sufficiently  rigid  to  bear  without  bending 
the  greatest  weight  that  the  construction  of  the  balance  admits  of  ; 
since  the  bending  of  the  beam  would  of  course  depress  the  points 
of  suspension  so  as  to  place  them  below  the  fulcrum,  and  this 
would,  as  we  have  just  seen,  tend  to  diminish  the  sensibility  of  the 
balance  in  proportion  to  the  increase  of  the  load.  It  is,  therefore, 
necessary  to  avoid  this  fault  by  a  proper  construction  of  the  beam. 
•  The  form  best  adapted  for  beams  is  that  of  an  isosceles  obtuse- 
angled  triangle,  or  of  a  rhombus. 

d.  The  arms  of  the  balance  must  be  of  equal  length,  i.  e.,  the 
points  of  suspension  must  be  equidistant  from  thefulcru7n^  for  if 
the  arms  are  of  unequal  length  the  balance  will  not  be  in  equili- 
brium, supposing  the  scales  to  be  loaded  with  equal  weights,  but 
there  will  be  preponderance  on  the  side  of  the  longer  arm. 

§5. 

The  SENSIBILITY  of  a  balance  depends  principally  upon  the  three 
following  conditions : — 

a.  The  friction  of  the  edges  upon  their  supports  must  be  as 
slight  as  possible.  The  greater  or  less  friction  of  the  edges  upon 
their  supports  depends  upon  both  the  form  and  material  of  those 
parts  of  the  balance.  The  edges  must  be  made  of  good  steel,  the 
supports  may  be  made  of  the  same  material ;  it  is  better,  however, 
that  the  centre  edge  at  least  should  rest  upon  an  agate  plane.  To 
form  a  clear  conception  of  how  necessary  it  is  that  even  the  end 
edges  should  have  as  little  friction  as  possible,  we  need  simply 
reflect  upon  what  would  happen  were  we  to  fix  the  scales  immov- 
bly  to  the  beam  by  means  of  rigid  rods.  Such  a  contrivance 
would  at  once  altogether  annihilate  the  sensibility  of  a  balance,  for 
if  a  weight  were  placed  upon  one  scale,  this  certainly  would  have 
a  tendency  to  sink ;  but  at  the  same  time  the  connecting  rods  be- 
ing compelled  to  form  constantly  a  right  angle  with  the  beam,  the 
weighted  scale  would  incline  inwards,  whilst  the  other  scale  would 
turn  outwards,  and  thus  the  arms  would  become  unequal,  the 
shorter  arm  being  on  the  side  of  the  weighted  scale,  whereby  the 
tendency  of  the  latter  to  sink  would  be  immediately  compensated 
for.  The  more  considerable  the  friction  becomes  at  the  end  edges 
of  a  balance,  the  more  the  latter  approaches  the  state  just  now 
described,  and  consequently  the  more  is  its  sensibility  impaired. 

/?.   The  centre  of  gravity  must  be  as  near  as  possible  to  theful- 


WEIGHING.  15 

crum.  The  nearer  the  centre  of  gravity  approaches  the  fulcrum, 
the  shorter  becomes  the  pendulum.  If  we  take  two  balls,  the  one 
suspended  by  a  short  and  the  other  by  a  long  thread,  and  impart 
the  same  impetus  to  both,  the  former  will  naturally  swing  at  a  far 
greater  angle  from  its  perpendicular  position  than  the  latter.  The 
same  must  of  course  happen  with  a  balance  ;  the  same  weight  will 
cause  the  scale  upon  which  it  is  placed  to  turn  the  more  rapidly 
and  completely,  the  shorter  the  distance  between  the  centre  of 
gravity  and  the  fulcrum.  We  have  seen  above,  that  in  a  balance 
where  the  three  edges  are  on  a  level  with  each  other,  increased 
loading  of  the  scales  will  continually  tend  to  raise  the  centre  of 
gravity  towards  the  fulcrum.  A  good  balance  will  therefore  be- 
come more  delicate  in  proportion  to  the  increase  of  weights  placed 
upon  its  scales ;  but,  on  the  other  hand,  its  sensibility  will  be  di- 
minished in  about  the  same  proportion  by  the  increment  of  the 
mass  to  be  moved,  and  by  the  increased  friction  attendant  upon 
the  increase  of  load ;  in  other  words,  the  delicacy  of  a  good  balance 
will  remain  the  same,  whatever  may  be  the  load  placed  upon  it. 
The  nearer  the  centre  of  gravity  lies  to  the  fulcrum,  the  slower  are 
the  oscillations  of  the  balance.  Hence  in  regulating  the  position 
of  the  centre  of  gravity  we  must  not  go  too  far,  for  if  it  ap- 
proaches the  fulcrum  too  nearly,  the  operation  of  weighing  will 
take  too  much  time. 

y.  The  beam  must  be  as  light  as  possible.  The  remarks  which 
we  have  just  now  made  will  likewise  show  how  far  the  weight  of 
the  beam  may  influence  the  sensibility  of  a  balance.  We  have  seen 
that  if  a  balance  is  not  actually  to  become  less  delicate  on  increased 
loading,  it  must  on  the  one  hand  have  a  tendency  to  become  more 
delicate  by  the  continual  approach  of  the  centre  of  gravity  to  the 
fulcrum.  ]N"ow  it  is  evident,  that  the  more  considerable  the  weight 
of  the  beam  is,  the  less  will  an  equal  load  placed  upon  both  scales 
alter  the  centre  of  gravity  of  the  whole  system,  the  more  slowly 
will  the  centre  of  gravity  approach  the  fulcrum,  the  less  will  the 
increased  friction  be  neutralized,  and  consequently  the  less  sensi- 
bility will  the  balance  possess.  Another  point  to  be  taken  into 
account  here  is,  that  the  moving  forces  being  equal,  a  lesser  mass 
or  weight  is  more  readily  moved  than  a  greater.  (§  4  a.) 

§6. 
We  will  now  proceed,  first,  to  give  the  student  a  few  general 


16  OPERATIONS. 

rules  to  guide  him  in  the  purchase  of  a  balance  intended  for  the 
purposes  of  quantitative  analysis ;  and,  secondly,  to  point  out  the 
best  method  of  testing  the  accuracy  and  sensibility  of  a  balance. 

1.  A  balance  able  to  bear  YO  or  80  grammes  in  each  scale,  suf- 
fices for  most  purposes. 

2.  The  balance  must  be  enclosed  in  a  glass  case  to  protect  it 
from  dust.      This  case  ought  to  be  sufficiently  large,  and,  more 
especially,  its  sides  should  not  approach  too  near  the  scales.     It 
must  be  constructed  in  a  manner  to  admit  of  its  being  opened  and 
closed  with  facility,  and  thus  to  allow  the  operation  of  weighing 
to  be  effected  without  any  disturbing   influence    from    currents 
of  air.     Therefore,  either  the  front  part  of  the  case  should  consist 
of  three  parts,  viz.,  a  fixed  centre  part  and  two  lateral  parts,  open- 
ing like  doors ;  or,  if  the  front  part  happens  to  be  made  of  one 
piece,  and  arranged  as  a  sliding-door,  the  two  sides  of  the  case  must 
be  provided  each  with  a  door. 

3.  The  balance  must  be  provided  with  a  proper  contrivance  to 
render  it  immovable  whilst  the  weights  are  being  placed  upon  the 
scale.     This  is  most  commonly  effected  by  an  arrangement  which 
enables  the  operator  to  lift  up  the  beam  and  thus  to  remove  the 
middle  edge  from  its  support,  whilst  the  scales  remain  suspended. 

It  is  highly  advisable  to  have  the  case  of  the  balance  so  arranged 
that  the  contrivances  for  lifting  the  beam  and  fixing  the  scales  can 
be  worked  while  the  case  remains  closed,  and  consequently  from 
without. 

4.  It  is  necessary  that  the  balance  should  be  provided  with  an 
index  to  mark  its  oscillations ;  this  index  is  appropriately  placed  at 
the  bottom  of  the  balance. 

5.  The  balance  must  be  provided  with  a  spirit  level,  to  enable 
the  operator  to  place  the  three  edges  on  an  exactly  horizontal  level ; 
it  is  best  also  for  this  purpose  that  the  case  should  rest  upon  three 
screws. 

6.  It  is  very  desirable  that  the  beam  should  be  graduated  into 
tenths,  so  as  to  enable  the  operator  to  weigh  the  milligramme  and 
its  fractions  with  a  centigramme  "  rider."* 

7.  The  balance  must  be  provided  with  a  screw  to  regulate  the 
centre  of  gravity,  and  likewise  with  two  screws  to  regulate  the 

*  [Becker's  later  balances  have  beams  graduated  to  twelfths,  and  a  rider 
weighing  12  mgrs.  This  enables  the  operator  to  use  nearly  the  whole  of  the 
graduation.] 


§    .7]  WEIGHING.  17 

equality  of  the  arms,  and  finally  with  screws  to  restore  the  equi- 
librium of  the  scales,  should  this  have  been  disturbed. 


The  following  experiments  serve  to  test  the  accuracy  and  sensi- 
bility of  a  balance.  . 

1.  The  balance  is,   in  the  first  place,  accurately  adjusted,  if 
necessary,  either  by  the  regulating  screws,  or  by  means  of  tinfoil, 
and  a  milligramme  weight  is  then  placed  in  one  of  the  scales.     A 
good  and  practically  useful  balance  must  turn  very  distinctly  with 
this  weight  ;  a  delicate  chemical  balance  should  indicate  the  -^  of 
a  milligramme  with  perfect  'distinctness. 

2.  Both  scales  are  loaded  with  the  maximum  weight  the  con- 
struction of  the  balance  will  admit  of  —  the  balance  is  then  accu- 
rately adjusted,  and  a  milligramme  added  to  the  weight  in  the  one 
scale.     This  ought  to  cause  the  balance  to  turn  to  the  same  extent 
as  in  1.     In  most  balances,  however,  it  shows  somewhat  less  on  the 
index.    It  follows  from  §  5  ft  that  the  balance  will  oscillate  more 
slowly  in  this  than  in  the  first  experiment. 

3.  The  balance  is  accurately  adjusted  (should  it  be  necessary 
to  establish  a  perfect  equilibrium  between  the  scales  by  loading  the 
one  with  a  minute  portion  of  tinfoil,  this  tinfoil  must  be  left  re- 
maining upon  the  scale  during  the  experiment)  ;  both  scales  are 
then  equally  loaded,  say,  with  fifty  grammes  each,  and,  if  neces- 
sary, the  balance   is   again   adjusted   (by  the   addition   of  small 
weights).     The  load  of  the  two  scales  is  then  interchanged,  so  as  to 
transfer  that  of  the  right  scale  to  the  left,  and  vice  versa.     A  bal- 
ance with  perfectly  equal  arms  must  maintain  its  absolute  equilib- 
rium upon  this  interchange  of  the  weights  of  the  two  scales. 

4.  The  balance  is  accurately  adjusted  ;  it  is  then  arrested  and 
again  set  in  motion  ;  the  same  process  should  be  repeated  several 
times.     A  good  balance  must  invariably  reassume  its  original  equi- 
librium.    A  balance  the  end  edges  of  which  afford  too  much  play 
to  the  hook  resting  upon  them,  so  as  to  allow  the  latter  slightly  to 
alter  its  position,  will   show  perceptible  differences  in  different 
trials.     This  fault,  however,  is  possible  only  with  balances  of  defec- 
tive construction. 

A  balance  to  be  practically  useful  for  the  purposes  of  quantita- 
tive analysis  must  stand  the  first,  second,  and  last  of  these  tests. 
A  slight  inequality  of  the  arms  is  of  no  great  consequence,  as  the 


18  OPERATIONS.  [§  8. 

error  that  it  would  occasion  may  be  completely  prevented  by  the 
manner  of  weighing. 

As  the  sensibility  of  a  balance  will  speedily  decrease  if  the  steel 
edges  are  allowed  to  get  rusty,  delicate  balances  should  never  be 
kept  in  the  laboratory,  but  always  in  a  separate  room.  It  is  also 
advisable  to  place  within  the  case  of  the  balance  a  vessel  half  filled 
with  calcined  carbonate  of  potassa,  to  keep  the  air  dry.  I  need 
hardly  add  that  this  salt  must  be  re-calcined  as  soon  as  it  gets, 
moist. 


b.  THE  WEIGHTS. 

1.  The  French  gramme  is  the  best  standard  for  calculation.     A 
set  of  weights  ranging  from  fifty  grammes  to  one  milligramme 
may  be  considered  sufficient  for  all  practical  purposes.     With  re- 
gard to  the  set  of  weights,  it  is  generally  a  matter  of  indifference 
for  scientific  purposes  whether  the  gramme,  its  multiples  arid  frac- 
tions, are  really  and  perfectly  equal  to  the  accurately  adjusted  nor- 
mal weights  of  the  corresponding  denominations  ;  *  but  it  is  abso- 
lutely necessary  that  they  should  agree  perfectly  with  each  other, 
i.  0.,  the  centigramme  weight  must  be  exactly  the  one  hundredth 
part  of  the  gramme  weight  of  the  set,  etc.  etc. 

2.  The  whole  of  the  set  of  weights  should  be  kept  in  a  suitable, 
well-closing  box ;  and  it  is  desirable  likewise  that  a  distinct  com- 
partment be  appropriated  to  every  one  even  of  the  smaller  weights. 

3.  As  to  the  shape  best  adapted  for  weights,  I  think  that  of 
short  frusta  of ' cones  inverted,  with  a  handle  at  the  top,  the  most 
convenient  and  practical  form  for  the  large  weights ;  square  pieces 
of  foil,  turned  up  at  one  corner,  are  best  adapted  for  the  small 
weights.     The  foil  used  for  this  purpose  should  not  be  too  thin,  and 
the  compartments  adapted  for  the  reception  of  the  several  smaller 
weights  in  the  box,  should  be  large  enough  to  admit  of  their  con- 
tents being  taken  out  of  them  with  facility,  or  else  the  smaller 
weights  will  soon  get  cracked,  bruised,  and  indistinct.     Every  one 

*  Still  it  would  be  desirable  that  mechanicians  who  make  gramme-weights 
intended  for  the  use  of  the  chemist,  should  endeavor  to  procure  normal  Aveights. 
It  is  very  inconvenient,  in  many  cases,  to  find  notable  differences  between 
weights  of  the  same  denomination,  but  coming  from  different  makers;  as  I  my- 
self have  often  had  occasion  to  discover. 


§  8.]  WEIGHING.  19 

of  the  weights  (with  the  exception  of  the  milligramme)  should  be 
distinctly  marked. 

4.  With  respect  to  the  material  most  suitable  for  the  manufac- 
ture of  weights,  we  commonly  rest  satisfied  with  having  the  smaller 
weights  only,  from  1  or  0'5  gramme  downwards,  made  of  plati- 
num or  aluminium  foil,  using  brass  weights  for  all  the  higher-de- 
nominations. Brass  weights  must  be  carefully  shielded  from  the 
contact  of  acid  or  other  vapors,  or  their  correctness  will  be  in- 
paired  ;  nor  should  they  ever  be  touched  with  the  fingers,  but 
always  with  small  pincers.  But  it  is  an  erroneous  notion  to  sup- 
pose that  weights  slightly  tarnished  are  unfit  for  use.  It  is,  in- 
deed, hardly  possible  to  prevent  weights  for  any  very  great  length  of 
time  from  getting  slightly  tarnished.  I  have  carefully  examined 
many  weights  of  this  description,  and  have  found  them  as  exactly 
corresponding  with  one  another  in  their  relative  proportions  as 
they  were  when  first  used.  The  tarnishing  coat,  or  incrustation, 
is  so  extremely  thin,  that  even  a  very  delicate  balance  will  gener- 
ally fail  to  point  out  any  perceptible  difference  in  the  weight. 

The  following  is  the  proper  way  of  testing  the  weights : 

One  scale  of  a  delicate  balance  is  loaded  with  a  one-gramme 
weight,  and  the  balance  is  then  completely  equipoised  by  taring 
with  small  pieces  of  brass,  and  finally  tinfoil  (not  paper,  since  this 
absorbs  moisture).  The  weight  is  then  removed,  and  replaced  suc- 
cessively by  the  other  gramme  weights,  and  afterwards  by  the 
same  amount  of  weight  in  pieces  of  lower  denominations. 

The  balance  is  carefully  scrutinized  each  time,  and  any  devi- 
ation from  the  exact  equilibrium  marked.  In  the  same  way  it  is 
seen  whether  the  two-gramme  piece  weighs  the  same  as  two  single 
grammes,  the  five-gramme  piece  the  same  as  three  single  grammes 
and  the  two-gramme  piece,  &c.  In  the  comparison  of  the  smaller 
weights  thus  among  themselves,  they  must  not  show  the  least  dif- 
ference on  a  balance  turning  with  ^  of  a  milligramme.  In  com- 
paring the  larger  weights  with  all  the  small  ones,  differences  of  jig- 
to  T2o-  of  a  milligramme  may  be  passed  over.  If  you  wish  them  to 
be  more  accurate,  you  must  adjust  them  yourself.  In  the  purchase 
of  weights  chemists  ought  always  to  bear  in  mind  that  an  accurate 
weight  is  truly  valuable,  whilst  an  inaccurate  one  is  absolutely 
worthless.  It  is  the  safest  way  for  the  chemist  to  test  every  weight 
he  purchases,  no  matter  how  high  the  reputation  of  the  maker. 


20  OPERATIONS.  [§   9. 

§  9- 
c.  THE  PROCESS  OF  WEIGHING. 

We 'have  two  different  methods  of  determining  the  weight  of 
substances ;  the  one  might  be  termed  direct  weighing,  the  other  is 
called  weighing  by  substitution. 

In  direct  weighing,  the  substance  is  placed  upon  one  scale,  and 
the  weight  upon  the  other.  If  we  possess  a  balance,  the  arms  of 
which  are  of  equal  length,  and  the  scales  in  a  perfect  state  of 
equilibrium,  it  is  indifferent  upon  which  scale  the  substance  is 
placed  in  the  several  weighings  required  during  an  analytical  pro- 
cess ;  i.e.,  we  may  weigh  upon  the  right  or  upon  the  left  side,  and 
change  sides  at  pleasure,  without  endangering  the  accuracy  of  our 
results.  But  if,  on  the  contrary,  the  arms  of  our  balance  are  not 
perfectly  equal,  or  if  the  scales  are  not  in  a  state  of  perfect  equili- 
brium, we  are  compelled  to  weigh  invariably  upon  the  same  scale, 
otherwise  the  correctness  of  our  results  will  be  more  or  less  materi- 
ally impaired. 

Suppose  we  want  to  weigh  one  gramme  of  a  substance,  and  to 
divide  this  amount  subsequently  into  two  equal  parts.  Let  us 
assume  our  balance  to  be  in  a  state  of  perfect  equilibrium,  but 
with  unequal  arms,  the  left  being  99  millimetres,  the  right  100 
millimetres  long ;  we  place  a  gramme  weight  upon  the  left  scale, 
and  against  this,  on  the  right  scale,  as  much  of  the  substance  to  be 
weighed  as  will  restore  the  equilibrium  of  the  balance. 

According  to  the  axiom,  "masses  are  in  equilibrium  upon  a 
lever,  if  the  products  of  their  weights  into  their  distances  from  the 
fulcrum  are  equal,"  we  have  consequently  upon  the  right  scale  0'99 
grm.  of  substance,  since  99xl'00=100x0'99.  If  we  now,  for  the 
purpose  of  weighing  one  half  the  quantity,  remove  the  whole 
weight  from  the  left  scale,  substituting  a  0'5  grm.  weight  for  it, 
and  then  take  off  part  of  the  substance  from  the  right  scale,  until 
the  balance  recovers  its  equilibrium,  there  will  remain  0'495  grm. ; 
and  this  is  exactly  the  amount  we  have  removed  from  the  scale : 
we  have  consequently  accomplished  our  object  with  respect  to  the 
relative  weight ;  and  as  we  have  already  remarked,  the  absolute 
weight  is  not  generally  of  so  much  importance  in  scientific  work. 
But  if  we  attempted  to  halve  the  substance  which  we  have  on  the 
right  scale,  by  first  removing  both  the  weiglit  and  the  substance 


§   9.]  WEIGHING.  21 

from  the  scales,  and  placing  subsequently  a  O5  grm.  weight  upon 
the  right  scale,  and  part  of  the  substance  upon  the  left,  until  the 
balance  recovers  its  equilibrium,  we  should  have  0*505  of  substance 
upon  the  left  scale,  since  100x0-500=99x0.505;  and  conse- 
quently, instead  of  exact  halves,  we  should  have  one  part  of  the 
substance  amounting  to  0'505,  the  other  only  to  0-485. 

If  the  scales  of  our  balance  are  not  in  a  state  of  absolute  equili- 
brium, we  are  obliged  to  weigh  our  substances  in  vessels  to  insure 
accurate  results  (although  the  arms  of  the  balance  be  perfectly 
equal).  It  is  self-evident  that  the  weights  in  this  case  must  like- 
wise be  invariably  placed  upon  one  and  the  same  scale,  and  that 
the  difference  between  the  two  scales  must  not  undergo  the 
slighest  variation  during  the  whole  course  of  a  series  of  experi- 
ments. 

From  these  remarks  result  the  two  following  rules  : — 

1.  It  is,  under  all  circumstances,  advisable  to  place  the  sub- 
stance invariably  upon  one  and  the  same  scale — most  conveniently 
upon  the  left. 

2.  If  the  operator  happens  to  possess  a  balance  for  his  own 
private  and  exclusive  use,  there  is  no  need  that  he  should  adjust  it 
at  the  commencement  of  every  analysis ;  but  if  the  balance  be  used 
in  common  by  several  persons,  it  is  absolutely  necessary  to  ascer- 
tain, before  every  operation,  whether  the  state  of  absolute  equili- 
brium may  not  have  been  disturbed. 

Weighing  by  substitution  yields  not  only  relatively,  but  also 
absolutely  accurate  results;  no  matter  whether  the  arms  of  the 
balance  be  of  exactly  equal  lengths  or  not,  or  whether  the  scales  be 
in  perfect  equipoise  or  not. 

The  process  is  conducted  as  follows :  the  material  to  be 
weighed — say  a  platinum  crucible — is  placed  upon  one  scale,  and 
the  other  scale  is  accurately  counterpoised  against  it.  The  plati- 
num crucible  is  then  removed,  and  the  equilibrium  of  the  balance 
restored  by  substituting  weights  for  the  removed  crucible.  It  is 
perfectly  obvious  that  the  substituted  weights  will  invariably 
express  the  real  weight  of  the  crucible  with  absolute  accuracy. 
We  weigh  by  substitution  whenever  we  require  the  greatest  pos- 
sible accuracy;  as,  for  instance,  in  the  determination  of  atomic 
weights.  The  process  may  be  materially  shortened  by  first  placing 
a  tare  (which  must  of  course  be  heavier  than  the  substance  to  be 
weighed)  upon  one  scale,  say  the  left,  and  loading  the  other  scale 


22  OPERATIONS.  [§  10. 

with  weights  until  equilibrium  is  produced.  This  tare  is  always 
retained  on  the  left  scale.  The  weights  after  being  noted  are 
removed.  The  substance  is  placed  on  the  right  scale,  together 
with  the  smaller  weights  requisite  to  restore  the  equilibrium  of 
the  balance.  The  sum  of  the  weights  added  is  then  subtracted 
from  the  noted  weight  of  the  counterpoise :  the  remainder  will  at 
once  indicate  the  absolute  weight  of  the  substance.  Let  us  sup- 
pose, for  instance,  we  have  on  the  left  scale  a  tare  requiring  a 
weight  of  fifty  grammes  to  counterpoise  it.  We  place  a  platinum 
crucible  on  the  right  scale,  and  find  that  it  requires  an  addition 
of  weight  to  the  extent  of  10  grammes  to  counterpoise  the  tare 
on  the  left.  Accordingly,  the  crucible  weighs  50  minus  10=40 
grammes. 

§10. 

The  following  rules  will  be  found  useful  in  performing  the 
process  of  weighing : — 

1.  The  safest  and  most  expeditious  way  of  ascertaining  the 
exact  weight  of  a  substance,  is  to  avoid  trying  weights  at  random  ; 
instead  of  this,  a  strictly  systematic  course  ought  to  be  pursued  in 
counterpoising  substances  on  the  balance.     Suppose,  for  instance, 
we  want  to  weigh  a  crucible,  the  weight  of  which  subsequently 
turns  out  to  be  6.627  grammes ;  well,  we  place  10  grammes  on  the 
other  scale  against  it,  and  we  find  this  is  too  much ;  we  place  the 
weight  next  in  succession,  i.e.,  5  grammes,  and  find  this  too  little ; 
next  Y,  too  much;  6,  too  little  ;  6'5,  too  little  ;  6'7,  too  much  ;  6'6, 
too  little  ;  6-65,  too  much  ;  6'62,  too  little  ;  6'63,  too  much  ;  6'625, 
too  little  ;  6-627,  right. 

I  have  selected  here,  for  the  sake  of  illustration,  a  most  com- 
plicated case ;  but  this  systematic  way  of  laying  on  the  weights 
will  in  most  instances  lead  to  the  desired  end,  in  half  the  time 
required  when  weights  are  tried  at  random.  After  a  little  prac- 
tice a  few  minutes  will  suffice  to  ascertain  the  weight  of  a  sub- 
stance to  within  the  y^  of  a  milligramme,  provided  the  balance 
does  not  oscillate  too  slowly. 

2.  The  milligrammes  and  fractions  of  milligrammes  are  deter- 
mined by  a  centigramme  rider  (to  be  placed  on  or  between  the 
divisions  on  the  beam)  far  more  expeditiously  and  conveniently 
than  by  the  use  of  the  weights  themselves,  and  at  the  same  time 
with  equal  accuracy. 


§   10.]  WEIGHING.  23 

3.  Particular  care  and  attention  should  be  bestowed  on  enter- 
ing the  weights  in  the  book.     The  best  way  is  to  write  down  the 
weights  first  by  inference  from  the  blanks,  or  gaps  in  the  weight 
box,   and   to   control    the   entry   subsequently   by   removing   the 
weights  from   the  scale,  and   replacing  them  in  their  respective 
-compartments  in  the   box.     The  student  should  from   the   com- 
mencement make  it  a  rule  to  enter  the  number  to  be  deducted  in 
the  lower  line  ;  thus,  in  the  upper  line,  the  weight  of  the  cruci- 
ble +  the  substance  ;  in  the  lower  line,  the  weight  of  the  empty 
crucible. 

4.  The  balance  ought  to  be  arrested  every  time  any  change  is 
contemplated,  such  as  removing  weights,  substituting  one  weight 
for  another,  tfcc.  etc.,  or  it  will  soon  get  spoiled. 

5.  Substances  (except,  perhaps,  pieces  of  metal,  or  some  other 
bodies  of  the  kind)  must  never  be  placed  directly  upon  the  scales, 
but  ought  to  be  weighed  in  appropriate  vessels  of  platinum,  silver, 
glass,  porcelain,  &c.,  never  on   paper  or  card,  since  these,  being 
liable  to  attract  moisture,  are  apt  to  alter  in  weight.  *  The  most 
common  method  is  to  weigh  in  the  first  instance  the  vessel  by 
itself,  and  to  introduce   subsequently  the   substance   into  it ;   to 
weigh  again,  and  subtract  the  former  weight  from  the  latter.     In 
many  instances,  and  more  especially  where  several  portions  of  the 
same  substance  are  to  be  weighed,  the  united  weight  of  the  vessel 
and  of  its  contents  is  first  ascertained ;  a  portion  of  the  contents 
is  then  shaken  out,  and  the  vessel  weighed  again ;  the  loss  of 
weight  expresses  the  amount  of  the  portion  taken  out  of  the  vessel. 

6.  Substances  liable  to  attract  moisture  from  the  air,  must  be 
weighed   invariably  in  closed   vessels   (in   covered   cru'cibles,  for 
instance,  or  between  two  watch-glasses,  or  in  a  closed  glass  tube); 
fluids  are  to  be  weighed  in  small  bottles  closed  with  glass  stoppers. 

7.  A  vessel  ought  never  to  be  weighed  whilst  warm,  since  it 
will  in  that  case  invariably  weigh  lighter  than  it  really  is.     This  is 
owing  to  two  circumstances.     In  the  first  place,  every  body  con- 
denses upon  its  surface  a  certain  amount  of  air  and  moisture,  the 
quantity  of  which  depends  upon  the  temperature  and  hygroscopic 
state  of  the  air,  and  likewise  on  its  own  temperature.     Now  sup- 
pose a  crucible  has  been  weighed  cold  at  the  commencement  of 
the   operation,    and   is   subsequently   weighed   again   whilst    hot, 
together  with  the  substance  it  contains,  and  the  weight  of  which 
we  wish  to  determine.     If  we    subtract    for    this    purpose    the 


24  OPERATIONS.  [§   11. 

weight  of  the  cold  crucible,  ascertained  in  the  former  instance, 
from  the  weight  found  in  the  latter,  we  shall  subtract  too  much, 
and  consequently  we  shall  set  down  less  than  the  real  weight  for 
the  substance.  In  the  second  place,  bodies  at  a  high  temperature 
are  constantly  communicating  heat  to  the  air  immediately  around 
them;  the  heated  air  expands  and  ascends,  and  the  denser  and 
colder  air,  flowing  towards  the  space  which  the  former  leaves,  pro- 
duces a  current  which  tends  to  raise  the  scale,  making  it  thus 
appear  lighter  than  it  really  is. 

8.  If  we  suspend  from  the  end  edges  of  a  correct  balance 
respectively  10  grammes  of  platinum  and  10  grammes  of  glass,  by 
wires  of  equal  weight,  the  balance  will  assume  a  state  of  equili- 
brium ;  but  if  we  subsequently  immerse  the  platinum  and  glass 
completely  in  water,  this  equilibrium  will  at  once  cease,  owing  to 
the  different  specific  gravity  of  the  two  substances ;  since,  as  is 
well  known,  substances  immersed  in  water  lose  of  their  weight 
a  quantity  equal  to  the  weight  of  their  own  bulk  of  water.  If 
this  be  borne  in  mind,  it  must  be  obvious  to  every  one  that 
weighing  in  the  air  is  likewise  defective,  inasmuch  as  the  bulk 
of  the  -substance  weighed  is  not  the  same  with  that  of  the 
weight.  This  defect,  however,  is  so  very  insignificant,  owing 
to  the  trifling  specific  gravity  of  the  air  in  proportion  to  that 
of  solid  substances,  that  we  may  generally  disregard  it  alto- 
gether in  analytical  experiments.  In  cases,  however,  where 
absolutely  accurate  results  are  required,  the  bulk  both  of 
the  substance  examined,  and  of  the  weight,  must  be  taken 
into  account,  and  the  weight  of  the  corresponding  volume 
of  air  added  respectively  to  that  of  the  substance  and  of 
the  weight,  making  thus  the  process  equivalent  to  weighing 
in  vacua. 

§11. 

2.  MEASURING. 

The  process  of  measuring  is  confined  in  analytical  researches 
mostly  to  gases  and  liquids.  The  method  of  measuring  gases  has 
been  brought  to  such  perfection  that  it  may  be  said  to  equal  in 
accuracy  the  method  of  weighing.  However,  such  accurate  meas- 
urements demand  an  expenditure  of  time  and  care,  which  can  be 


•§   12.]  MEASUKIX(T    OF    (4 ASKS.  25 

bestowed  only  on  the  nicest  and  most  delicate  scientific  investiga- 
tions.* 

The  measuring  of  liquids  in  analytical  investigations  was  resorted 
to  first  by  DESCROIZILLES  ("  Alkali  meter,"  1806).  GAY-LUSSAC 
materially  improved  the  process,  and  indeed  brought  it  to  the 
highest  degree  of  perfection  (measuring  of  the  solution  of  chloride 
of  sodium  in  the  assay  of  silver  in  the  wet  way).  More  recently 
F.  MOHR+  has  bestowed  much  care  and  ingenuity  upon  the  pro- 
duction of  appropriate  and  convenient  measuring  apparatus,  and 
has  added  to  our  store  the  eminently  practical  compression  stop- 
cock burette.  The  process  is  now  resorted  to  even  in  most  accurate 
scientific  investigations,  since  it  requires  much  less  time  than  the 
process  of  weighing. 

The  accuracy  of  all  measurings  depends  upon  the  proper  con- 
struction of  the  measuring  vessels,  and  also  upon  the  manner  in 
which  the  process  is  conducted. 


a.  THE  MEASURING  OF  GASES. 

We  use  for  the  measuring  of  gases  graduated  tubes  of  greater 
or  less  capacity,  made  of  strong  glass,  and  closed  by  fusion  at  one 
end,  which  should  be  rounded.  The  following  tubes  will  be  found 
sufficient  for  all  the  processes  of  gas  measuring  required  in  organic 
elementary  analyses. 

1.  A  bell-glass  capable  of  holding  from  150  to  250  c.  c.,  and 
about  4  centimetres  in  diameter ;  divided  into  cubic  centimetres. 

2.  Five  or  six  glass  tubes,  about  12  to  15  millimetres  in  diam- 
eter in  the  clear,  and  capable  of  holding  from  30  to  40  c.  c.  each, 
divided  into  -^  c.  c. 

The  sides  of  these  tubes  should  be  pretty  thick,  otherwise  they 
will  be  liable  to  break,  especially  when  used  to  measure  over  mer- 
cury. The  sides  of  the  bell-glass  should  be  about  3,  of  the  tubes 
about  2  millimetres  thick.  , 

The  most  important  point,  however,  in  connection  with  meas- 

*  [The  student  who  will  practise  the  accurate  measurement  of  gases  in  any 
but  the  simplest  cases,  must  refer  for  all  details  to  Bunsen's  "Gasometry" 
(translated  by  Roscoe),  and  Russell,  Jour.  Chem.  Soc.,  1868,  p.  128,  as  the  sub- 
ject is  too  extensive  for  the  limits  of  this  volume.] 

t  "Lehrbuch  der  Titrirmethode,"  by  Dr.  Fr.  Mohr.     Brunswick,  1855. 


26  OPERATIONS.  [§    12, 

uring  instruments  is  that  the}7  be  correctly  graduated,  since  upon 
this  of  course  depends  the  accuracy  of  the  results.  For  the  method 
of  graduating  I  refer  to  GREVILLE  WILLIAMS'  u  Chemical  Mani- 
pulation."* 

In  testing  the  measuring  tubes  we  have  to  consider  three 
things. 

1.  Do  the  divisions  of  a  tube  correspond  with  each  other? 

2.  Do  the  divisions  of  each  tube  correspond  with  those  of  the 
other  tubes  ? 

3.  Do  the  volumes  expressed   by  the  graduation   lines  corre- 
spond with  the  weights  used  by  the  analyst  ? 

These  three  questions  are  answered  by  the  following  experi- 
ments : 

a.  The  tube  which  it  is  intended  to  examine  is  placed  in  a  per- 
pendicular position,  and  filled  gradually  with  accurately  measured 
small  quantities  of  mercury,  care  being  taken  to  ascertain  with  the 
utmost  precision  wThether  the  graduation  of  the  tube  is  proportion- 
ate to  the  equal  volumes  of  mercury  poured  in.  The  measuring- 
off  of  the  mercury  is  effected  by  means  of  a  small  glass  tube,  sealed 
at  one  end,  and  ground  perfectly  even  and  smooth  at  the  other. 
This  tube  is  filled  to  overflowing  by  immersion  under  mercury, 
care  being  taken  to  allow  no  air  bubbles  to  remain  in  it ;  the 
excess  of  mercury  is  then  removed  by  pressing  a  small  glass  plate 
down  on  the  smooth  edge  of  the  tube.f 

5.  Different  quantities  of  mercury  are  successively  measured 
off  in  one  of  the  smaller  tubes,  and  then  transferred  into  the  other 
tubes.  The  tubes  may  be  considered  in  perfect  accordance  with 
each  other,  if  the  mercury  reaches  invariably  the  same  divisional 
point  in  every  one  of  them. 

Such  tubes  as  are  intended  simply  to  determine  the  relative 
volume  of  different  gases,  need  only  pass  these  two  experiments ; 
but  in  cases  where  we  want  to  calculate  the  weight  of  a  gas  from 
its  yolume,  it  is  necessary  also  to  obtain  an  answer  to  the  third 
question.  For  this  purpose — 

c.  One  of  the  tubes  is  accurately  weighed  and  then  filled  with 


*  [See  also  Gary  Lea,  Am.  Jour.  Sci.  and  Arts,  2d  ser.,  vol.  42,  p.  375.] 
f  As  warming  the  metal  is  to  be  carefully  avoided  in  this  process,  it  is  advi- 
sable not  to  hold  the  tube  with  the  hand  in  immersing  it  in  the  mercury,  but  to 
fasten  it  in  a  small  wooden  holder. 


§   13.J  MEASURING    OF    GASKS.  27 

distilled  water  of  a  temperature  of  16°  to  the  last  mark  of  the 
graduated  scale ;  the  weight  of  the  water  is  then  accurately  deter- 
mined. If  the  tube  agrees  with  the  weights,  every  100  c.  c.  of 
water  of  16°  must  weigh  99*9  grrn.  But  should  it  not  agree,  no 
matter  whether  the  error  lie  in  the  graduation  of  the  tube  or  in 
the  adjustment  of  the  weights,  we  must  apply  a  correction  to  the 
volume  observed  before  calculating  the  weight  of  a  gas  therefrom. 
Let  us  suppose,  for  instance,  that  we  find  100  c.  c.  to  weigh  only 
99'6  grm. :  assuming  our  weights  to  be  correct,  the  c.  c.  of  our 
scale  are  accordingly  too  small ;  and  to  convert  100  of  these  c.  c. 
into  normal  c.  c.  we  say  : — 

99-9  :.99-6  ::  luO  :  ,/•. 

In  the  measuring  of  gases  we  must  have  regard  to  the  follow- 
ing points : — 

1.  Correct  reading-off.  2.  The  temperature  of  the  gas.  3.  The 
degree  of  pressure  operating  upon  it.  And  4.  The  circumstance 
whether  it  is  dry  or  moist.  The  three  latter  points  will  be  readily 
understood,  if  it  be  borne  in  mind  that  any  alteration  in  the  tem- 
perature of  a  gas,  or  in  the  pressure  acting  upon  it,  or  in  the  ten- 
sion of  the  admixed  aqueous  vapor,  involves  likewise  a  consider- 
able alteration  in  its  volume. 

§13. 
1.  CORRECT  READING-OFF. 

This  is  rather  difficult,  since  mercury  in  a  cylinder  has  a  con- 
vex surface  (especially  observable  with  a  narrow  tube),  owing  to 
its  own  cohesion;  whilst  water,  on  the  other  hand,  under  the  same 
circumstances  has  a  concave  surface,  owing  to  the  attraction  which 
the  walls  of  the  tube  exercise  upon  it.  The  cylinder  should 
invariably  be  placed  in  a  perfectly  perpendicular  position,  and  the 
eye  of  the  operator  brought  to  a  level  with  the  surface  of  the 
fluid. 

In  reading-off  over  water,  the  middle  of  the  dark  zone  formed 
by  that  portion  of  the  liquid  that  is  drawn  up  around  the  inner 
walls  of  the  tube,  is  assumed  to  be  the  real  surface ;  whilst  when 
operating  with  mercury,  we  have  to  place  the  real  surface  in  a 
plane  exactly  in  the  middle  between  thp  highest  point  of  the  sur- 
face of  the  mercury,  and  the  points  at  which  the  latter  is  in  actual 


28  OPERATIONS.  [§   14. 

contact  with  the  walls  of  the  tube.     However,  the  results  obtained 
in  this  way  are  only  approximate. 

Absolutely  accurate  results  cannot  be  arrived  at,  in  measuring 
over  water  or  any  other  fluid  that  adheres  to  glass.  But  over  mer- 
cury they  may  be  arrived  at  if  the  error  of  the  meniscus  be  deter- 
mined and  the  mercury  be  read  off  at  the  highest  point.  The 
determination  of  the  error  of  the  meniscus  is  performed  for  each 
tube,  once  for  all,  in  the  following  manner :  some  mercury  is 
poured  into  the  tube,  and  its  height  read-off  right  on  a  level  with 
the  top  of  the  convex  surface  exhibited  by  it;  a  few  drops  of  solu- 
tion of  chloride  of  mercury  are  then  poured  on  the  top  of  the 
metal ;  this  causes  the  convexity  to  disappear ;  the  height  of  the 
mercury  in  the  tube  is  now  read-off  again  and  the  difference  noted. 
In  the  process  of  graduation,  the  tube  stands  upright,  in  that  of 
measuring  gases,  it  is  placed  upside  down ;  the  difference  observed 
must  accordingly  be  doubled,  and  the  sum  added  to  each  volume 
of  gas  read  off. 

§14. 
2.  INFLUENCE  OF  TEMPERATURE. 

The  temperature  of  gases  to  be  measured  is  determined  either 
by  making  it  correspond  with  that  of  the  confining  fluid,  and 
ascertaining  the  latter,  or  by  suspending  a  delicate  thermometer 
by  the  side  of  the  gas  to  be  measured,  and  noting  the  degree  which 
it  indicates. 

If  the  construction  of  the  pneumatic  apparatus  permits  the 
total  immersion  of  the  cylinder  in  the  confining  fluid,  uniformity 
of  temperature  between  the  latter  and  the  gas  which  it  is  intended 
to  measure,  is  most  readily  and  speedily  obtained ;  but  in  the 
reverse  case,  the  operator  must  always,  after  every  manipulation, 
allow  half  an  hour  or,  in  operations  combined  with  much  heating, 
even  an  entire  hour  to  elapse,  before  proceeding  to  observe  the 
state  of  the  mercury  in  the  cylinder,  and  in  the  thermometer. 

Proper  care  must  also  be  taken,  after  the  temperature  of  the 
gas  has  been  duly  adjusted,  to  prevent  re-expansion  during  the 
reading-off ;  all  injurious  influences  in  this  respect  must  accord- 
ingly be  carefully  guarded  against,  and  the  operator  should,  more 
especially,  avoid  laying  hold  of  the  tube  with  his  hand  (in  pressing 
it  down,  for  instance,  into  the  confining  fluid) ;  making  use, 
instead,  of  a  wooden  Holder. 


§§    15,    16.J  MEASUKIXG    OF    GASES.  29 

§  15. 

3.  INFLUENCE  OF  PRESSURE. 

With  regard  to  the  third  point,  the  gas  is  under  the  actual 
pressure  of  the  atmosphere  if  the  confining  fluid  stands  on  an 
exact  level  both  in  and  outside  the  cylinder ;  the  degree  of  pres- 
sure exerted  upon  it  may  therefore  at  once  be  ascertained  by  con- 
sulting the  barometer.  But  if  the  confining  fluid  stands  higher  in 
the  cylinder  than  outside,  the  gas  is  under  less  pressure, — if  lower, 
it  is  under  greater  pressure  than  that  of  the  atmosphere ;  in  the 
latter  case,  the  perfect  level  of  the  fluid  inside  and  outside  the 
cylinder  may  readily  be  restored  by  raising  the  tube ;  if  the  fluid 
stands  higher  in  the  cylinder  than  outside,  the  level  may  be 
restored  by  depressing  the  tube ;  this  however  can  only  be  done 
in  cases  where  we  have  a  trough  of  sufficient  depth.  When  oper- 
ating over  water,  the  level  may  in  most  cases  be  readily  adjusted ; 
when  operating  o'ver  mercury,  it  is,  more  especially  with  wide 
tubes,  often  impossible  to  bring  the  fluid  to  a  perfect  level  inside 
and  outside  the  cylinder. 

§16. 

4.  INFLUENCE  OF  MOISTURE. 

In  measuring  gases  saturated  with  aqueous  vapor,  it  must  be 
taken  into  account  that  the  vapor,  by  virtue  of  its  tension,  exerts  a 
pressure  upon  the  confining  fluid.  The  necessary  correction  is 
simple,  since  we  knowr  the  respective  tension  of  aqueous  vapor  for 
the  various  degrees  of  temperature.  But  before  this  correction 
can  be  applied,  it  is,  of  course,  necessary  that  the  gas  should  be 
actually  saturated  with  the  vapor.  It  is,  therefore,  indispensable 
in  measuring  gases  to  take  care  to  have  the  gas  thoroughly  satu- 
rated with  aqueous  vapor,  or  else  absolutely  dry. 


It  is  quite  obvious  from  the  preceding  remarks,  that  volumes 
of  gases  can  be  compared  only  if  measured  at  the  same  temper- 
ature, under  the  same  pressure,  and  in  the  same  hygroscopic  state. 
They  are  generally  reduced  to  0°,  0'76  met.  barometer,  and  abso- 
lute dryness.  How  this  is  effected,  as  well  as  the  manner  in  which 
we  deduce  the  weight  of  gases  from  their  volume,  will  be  found 
in  the  chapter  on  the  calculation  of  analyses. 


30  OPERATIONS.  [§§  17,   18. 

§17. 
b.  THE  MEASURING  OF  FLUIDS. 

In  consequence  of  the  vast  development  which  volumetric 
analysis  has  of  late  acquired,  the  measuring  of  fluids  has  become  an 
operation  of  very  frequent  occurrence.  According  to  the  different 
objects  in  view,  various  kinds  of  measuring  vessels  are  employed. 
The  operator  must,  in  the  case  of  every  measuring  vessel,  carefully 
distinguish  whether  it  is  graduated  for  holding  or  for  delivering 
the  exact  number  of  c.  c.  marked  on  it.  If  you  have  made  use  of 
a  vessel  of  the  former  description  in  measuring  off  100  c.  c.  of  a 
fluid,  and  wish  to  transfer  the  latter  completely  to  another  vessel, 
you  must,  after  emptying  your  measuring  vessel,  rinse  it,  and  add 
the  rinsings  'to  the  fluid  transferred ;  whereas,  if  you  have  made 
use 'of  a  measuring  vessel  of  the  latter  description,  there  must  be 
no  rinsing. 

a.  MEASURING  VESSELS  GRADUATED  FOR  HOLDING  THE  EXACT  MEAS- 
URE  OF   FLUID   MARKED   ON   THEM. 

aa.  Measuring  vessels  which  serve  to  measure  out  one  definite 
quantity  of  fluid. 

We  use  for  this  purpose — 

§18. 
1.  Measuring  Flasks. 

Fig.  2  represents  a  measuring  flask  of  the  most  practical  and 
convenient  form. 

Measuring  flasks  of  various  sizes  are  sold  in  the  shops,  holding 
respectively  200,  250,  500,  1000,  2000,  &c.,  c.  c.  As  a  general 
rule,  they  have  no  ground-glass  stoppers ;  it  'is,  however,  very 
desirable,  in  certain  cases,  to  have  measuring  flasks  with  ground 
stoppers.  The  flasks  must  be  made  of  well-annealed  glass  of  uni- 
form thickness,  so  that  fluids  may  be  heated  in  them.  The  line- 
mark  should  be  placed  within  the  lower  third,  or  at  least  within 
the  lower  half,  of  the  neck. 


§   18.]  MEASURING   OF   FLUIDS.  31 

Measuring  flasks,  before  they  can  properly  be  employed  in 
analytical  operations,  must  first  be  carefully 
tested.  The  best  and  simplest  way  of 
effecting  this  is  to  proceed  thus  : — Put  the 
flask,  perfectly  dry  inside  and  outside,  on 
the  one  scale  of  a  sufficiently  delicate  bal- 
ance, together  with  a  weight  of  1000  grm. 
in  the  case  of  a  litre  flask,  500  grm.  in  the 
case  of  a  half -litre  flask,  etc.,  restore  the 
equilibrium  by  placing  the  requisite  quan- 
tity of  shot  and  tinfoil  on  the  other  scale, 
then  remove  the  flask  and  the  weight  from 
the  balance,  put  the  flask  on  a  perfectly 

level  surface,  and  pour  in  distilled  water  of  16°,*  until  the  lower 
border  of  the  dark  zone  formed  by  the  top  of  the  water  around 
the  inner  walls  corresponds  with  the  line-mark.  After  having 
thoroughly  dried  the  neck  of  the  flask  above  the  mark,  replace  it 
upon  the  scale  :  if  this  restores  the  perfect  equilibrium  of  the  bal- 
ance, the  water  in  the  flask  wreighs,  in  the  case  of  a  litre  measure, 
exactly  1000  grm.  If  the  scale  bearing  the  flask  sinks,  the  water 
in  it  weighs  as  much  above  1000  grm.  as  the  additional  weights 
amount  to  which  you  have  to  put  in  the  other  scale  to  restore  the 
equilibrium ;  if  it  rises,  on  the  other  hand,  the  water  weighs  as 
much  less  as  the  weights  amount  to  which  you  have  to  put  in  the 
scale  with  the  flask  to  effect  the  same  end. 

*To  use  water  in  the  state  of  its  highest  density,  viz.,  of  4°,  1  c.  c.  of  which 
weighs  exactly  1  grm.,  and,  accordingly,  1  litre,  exactly  1000  grms.,  is  less  prac- 
tical, as  the  operations  must  in  that  case  be  conducted  in  a  room  as  cold ;  since, 
in  a  warmer  room,  the  outside  of  the  flask  would  immediately  become  covered 
with  moisture,  in  consequence  of  the  air  cooling  below  dew-point.  Nor  can  I 
recommend  F  Mohr's  suggestion  to  make  litre-flasks,  and  measuring  vessels  in 
general,  upon  a  plan  to  make  the  litre-flask,  for  instance,  hold,  not  1000  grm. 
water  at  4°,  but  1000  grm.  at  16°,  since  in  an  arrangement  of  the  kind  proper 
regard  is  not  paid  to  the  actual  meaning  of  the  term  "litre"  in  the  scientific 
world ;  and  measuring  vessels  of  the  same  nominal  capacity,  made  by  different 
instrument-makers,  are  thus  liable  to  differ  to  a  greater  or  less  extent.  One  litre- 
flask,  according  to  Mohr,  holds  1001  '2  standard  c.  c.  I  consider  it  impractical 
to  give  to  the  c.  c.  another  signification  in  vessels  intended  for  measuring  fluids 
than  in  vessels  used  for  the  measuring  of  gases,  which  latter  demand  strict  ad- 
hesion to  the  standard  c.  c. ,  as  it  is  often  required  to  deduce  the  weight  of  a  gas 
by  calculating  from  the  volume. 


OPERATIONS. 


[ 


If  the  water  in  the  litre  measure  weighs  999  grm.,*  in  the  half- 
litre  measure,  499'5  grm.,  &c.,  the  measuring  flasks  are  correct. 
Differences  up  to  O'lOO  grm.,  in  the  litre  measure,  up  to  0.070  grm. 
in  the  half-litre  measure,  and  up  to  0'050  grm.  in  the  quarter-litre 
measure,  are  not  taken  into  account,  as  one  and  the  same  measur- 
ing flask  will  be  found  to  offer  variation  to  the  extent  indicated,  in 
repeated  consecutive  weighings,  though  filled  each  .time  exactly  up 
to  the  mark  with  water  of  the  same  temperature. 
Though  a  flask  should,  upon  examination, 
turn  out  not  to  hold  the  exact  quantity  of  water 
which  it  is  stated  to  contain,  it  may  yet  possibly 
agree  with  the  other  measuring  vessels,  and  may 
accordingly  still  be  perfectly  fit  for  use  for  most 
purposes.  Two  measuring  vessels  agree  among 
themselves  if  the  marked  Nos.  of  c.  c.  bear  the 
same  proportion  to  each  other  as  the  weights 
found ;  thus,  for  instance,  supposing  your  litre- 
measure  to  hold  998  grm.  water  of  16°,  and  your 
50  c.  c.  pipette  to  deliver  49'9  grm.  water  of  the 
same  temperature,  the  two  measures  agree,  since 


100 


90 


80 


70 


60 


50 


40 


1000  :  50  =  998  :  49-9. 


To  prepare  or  correct  a  measuring  flask,  tare 
the  dry  litre,  half-litre,  or  quarter-litre  flask,  and 
then  weigh  into  it,  by  substitution,  (§  9)  999 
grrn.,  or,  as  the  case  may  be,  the  half  or  quarter 
of  that  quantity  of  distilled  water  of  16°.  Put 
the  flask  on  a  perfectly  horizontal  support,  place 
your  eye  on  an  exact  level  with  the  surface  of 
the  water,  and  mark  the  lower  border  of  the  dark 
zone  by  two  little  dots  made  on  the  glass  with  a  point  dipped  into 
thick  asphaltum  varnish,  or  some  other  substance  of  the  kind.  Now 
pour  out  the  water,  place  the  flask  in  a  convenient  position,  and 
cut  with  a  diamond  a  fine  distinct  line  into  the  glass  from  one  dot 
to  the  other. 

lib.  Measuring  vessels  which  serve  to  measure  out  any  quanti- 
ties of  fluid  cut  will. 


*  With  absolute  accuracy,  998-981  grm. 


^  19,   20.]  MEASURING   OF    FLUIDS.  33 

'    §19- 

2.   The  Graduated  Cylinder. 

This  instrument,  represented  in  fig.  3,  should  be  from  2  to 
3  cm.  wide,  of  a  capacity  of  100 — 300  c.  c.,  and  divided  into 
single  c.  c.  It  must  be  ground  at  the  top,  that  it  may  be 
covered  quite  close  with  a  ground-glass  plate.  The  measuring 
with  such  cylinders  is  not  quite  so  accurate  as  with  measuring 
flasks,  as  in  the  latter  the  volume  is  read  off  in  a  narrower  part. 
The  accuracy  of  measuring  cylinders  may  be  tested  in  the  same  way 
as  in  the  case  of  measuring  flasks,  viz.,  by  weighing  into  them  water 
of  16°  ;  or,  also,  very  well,  by  letting  definite  quantities  of  fluid  flow 
into  the  cylinder  from  a  correct  pipette,  or  burette  graduated  for 
delivering,  and  observing  whether  or  not  they  are  correctly  indi- 
cated by  the  scale  of  the  cylinder. 

ft.  MEASURING  VESSELS   GRADUATED   FOR   DELIVERING   THE   EXACT 
MEASURE  OF  FLUID  MARKED  ON  THEM  (graduated  d  Pecoiilemeitt i. 

aa.  Measuring  vessels  which  serve  to  measure  out  one  definite 
quantity  of  fluid. 

§20. 
3.  TJie  Graduated  Pipette. 

This  instrument  serves  to  take  out  a  definite  volume  of  a  fluid 
from  one  vessel,  and  to  transfer  it  to  another ;  it  must  accordingly 
be  of  a  suitable  shape  to  admit  of  its  being  freely  inserted  into 
flasks  and  bottles. 

We  use  pipettes  of  1,  5,  10,  20,  50,  100,  150,  and  200  c.  c. 
capacity.  The  proper  shape  for  pipettes  up  to  20  c.  c.  capacity  is 
represented  in  fig.  4 ;  fig.  5  shows  the  most  practical  form  for  lar- 
ger ones.  To  fill  a  pipette  suction  is  applied  to  the  upper  aper- 
ture, either  directly  with  the  lips  or  through  a  caoutchouc  tube, 
until  the  fluid  stands  above  the  mark ;  the  upper  orifice  (which  is 
somewhat  narrowed  and  ground)  is  then  closed  with  the  first  finger 
of  the  right  hand  (the  point  of  which  should  be  a  little 
moist) ;  the  outside  is  then  wiped  dry,  if  required,  and,  the 
pipette  being  held  in  a  perfectly  vertical  direction,  the  fluid 
Is  made  to  drop  out,  by  lifting  the  .  finger  a  little,  till  it  has 


OPERATIONS; 


[§  20. 


fallen  to  the  required  level;  the  loose  drop  is  carefully  wiped 
off,  and  the  contents  of  the  tube  are  then  finally  transferred  to 
the  other  vessel.  In  this  process  it  is  found  that  the  fluid  does 
not  run  out  completely,  but  that  a  small  portion  of  it  remains 
adhering  to  the  glass  in  the  point  of  the  pipette ;  after  a  time,  as 
this  becomes  increased  by  other  minute  particles  of  fluid  trickling 
down  from  the  upper  part  of  the  tube, 
a  drop  gathers  at  the  lower  orifice,  which 
may  be  allowed  to  fall  off  from  its  own 
weight,  or  may  be  made  to  drop  off  by  a 
slight  shake.  If,  after  this,  the  point  of  the 
pipette  be  laid  against  a  moist  portion  of 
the  inner  side  of  the  vessel,  another  minute 
portion  of  fluid  will  trickle  out,  and,  lastly, 
another  trifling  droplet  or  so  may  be  got 
out  by  blowing  into  the  pipette.  Now, 
supposing  the  operator  follows  no  fixed  rule 
in  this  respect,  letting  the  fluid,  for  instance, 
in  one  operation  simply  run  out,  whilst  in 
another  operation  he  lets  it  drain  afterwards, 
and  in  a  third  blows  out  the  last  particles 
of  it  from  the  pipette,  it  is  evident  that  the 
respective  quantities  of  fluid  delivered  in 
the  several  operations  cannot  be  quite  equal. 
I  prefer  in  all  cases  the  second  method,  viz., 
to  lay  the  point  of  the  pipette,  whilst  drain^ 
ing,  finally  against  a  moist  portion  of  the 
side  of  the  vessel,  which  I  have  always  found 
to  give  the  most  accurately  corresponding 
measurements. 

The  correctness  of  a  pipette  is  tested 
by  filling  it  up  to  the  mark  with  distilled 
water  of  16°,  letting  the  water  run  out,  in 
Fig.  4.     Fig.  5.    Fig.  6.    t}ie  manner  jlist  stated,  into  a  tared  vessel, 
and  weighing ;  the  pipette  may  be  pronounced  correct  if  100  c.  c. 
of  water  of  16°  weigh  99*9  grin. 

Testing  in  like  manner  the  accuracy  of  the  measurements  made 
with  a  simple  hand  pipette,  we  find  that  one  and  the  same  pipette 
will  in  repeated  consecutive  weighings  of  the  contents,  though 


§    20.]  MEASURING    OF    FLUIDS.  35 

tilled  and  emptied  each  time  with  the  minutest  care,  show  differ- 
ences up  to  O010  grin,  for  10  c.  c.  capacity,  up  to  0*0±0  grm.  for 
50  c.  c.  capacity. 

The  accuracy  of  the  measurements  made  with  a  pipette  may 
be  heightened  by  giving  the  instrument  the  form  and  construction 
shown  in  fig.  6,  and  fixing  it  to  a  holder. 

It  will  be  seen  from  the  drawing  that  these  pipettes  are 
emptied  only  to  a  certain  mark  in  the  lower  tube,  and  that  they 
are  provided  with  a  compression  stop-cock,  a  contrivance  which  we 
shall  have  occasion  to  describe  in  detail  when  oh  the  subject  of 
burettes.  This  contrivance  reduces  the  differences  of  measure- 
ments with  one  and  the  same  50  c.  c.  pipette  to  0'005  grm. 

Pipettes  are  used  more  especially  in  cases  where  it  is  intended 
to  estimate  different  constituents  of  a  substance  in  separate  por- 
tions of  the  same :  for  instance,  10  grm.  of  the  substance  under 
examination  are  dissolved  in  a  250  c.  c.  flask,  the  solution  is  dilu- 
ted up  to  the  mark,  shaken,  and  2,  3,  or  4  several  portions  are  then 
taken  out  with  a  50  c.  c.  pipette.  Each  portion  consists  of  \  part 
of  the  whole,  and  accordingly  contains  2  grm.  of  the  substance. 
Of  course  the  pipette  and  the  flask  must  be  in  perfect  harmony. 
Whether  they  are  may  be  ascertained  by,  for  instance,  emptying 
the  50  c.  c.  pipette  5  times  into  the  250  c.  c.  flask,  and  observing 
if  the  lower  edge  of  the  dark  zone  of  fluid  coincides  with  the 
mark.  If  it  does  not,  you  may  make  a  fresh  mark,  which,  no 
matter  whether  it  is  really  correct  or  not,  will  bring  the  two  instru- 
ments in  question  into  conformity  with  each  other. 

Cylindrical  pipettes,  graduated  throughout  their  entire  length, 
may  be  used  also  to  measure  out  any  given  quantities  of  liquid ; 
however,  these  instruments  can  properly  be  employed  only  in  pro- 
cesses where  minute  accuracy  is  not  indispensable,  as  the  limits  of 
error  in  reading  off  the  divisions  in  the  wider  part  of  the  tube  are 
not  inconsiderable.  For  smaller  quantities  of  liquid  this  inaccu- 
racy may  be  avoided  by  making  the  pipettes  of  tubes  of  uniform 
width,  having  a  small  diameter  only,  and  narrowed  at  both  ends. 
(FR.  MOHR'S  measuring  pipettes.) 

When  a  fluid  runs  out  of  a  pipette,  drops  sometimes  remain 
here  and  there  adhering  to  the  tube ;  this  arises  from  a  film  of  fat 
on  the  inside  ;  it  may  be  removed  by  keeping  the  instrument  some 
time  filled  with  a  solution  of  bichromate  of  potassa  mixed  with 
sulphuric  acid. 


36 


OPERATIONS. 


[§21. 


bb.  Measuring  vessels  which  serve  to  measure  out  quantities  of 
fluid  at  will. 

4.  The  Burette. 

Of  the  various  forms  and  dispositions  of  this  instrument,  the 
following  appear  to  me  the  most  convenient : — 


I.  Mohr's  Burette,  (Compression  cock  burette). 

For  this  excellent  measuring  apparatus,  which  is  represented  in 
fig.  7,  we  are  indebted  to  FR.  MOHR.  It  consists  of  a  cylindrical 
tube,  narrower  towards  the  lower  end  for  about  an  inch,  with  a 


§  21.]  MEASURING  OF    FLUIDS.  37 

slight  widening,  however,  at  the  extreme  point,  in  order  that  the 
caoutchouc  connector  may  take  a  firm  hold.  I  only  use  burettes 
of  two  sizes,  viz..  of  30  c.  c.,  divided  into  ^  c.  c.;  and  of  50  c.  c., 
divided  into  J  c.  c.  The  former  I  employ  principally  in  scientific, 
the  latter  chiefly  in  technical  investigations.  The  usual  length  of 
my  30  c.  c.  burette  is  about  50  cm.;  the  graduated  portion  occupies 
about  49  cm.  The  diameter  of  the  tube  is  accordingly  about  10 
mm.  in  the  clear  ;  the  upper  orifice  is,  for  the  convenience  of  filling, 
widened  in  form  of  a  funnel,  measuring  20  mm.  in  diameter ;  the 
width  of  the  lower  orifice  is  5  mm.  For  very  delicate  processes, 
the  length  of  the  graduated  portion  may  be  extended  to  50  or  52 
cm.,  leaving  thus  intervals  of  nearly  2  mm.  between  the  small 
divisional  lines.  In  my  50  c.  c.  burettes  the  graduated  portion  of 
the  tube  is  generally  40  cm.,  long. 

To  make  the  instrument  ready  for  .use,  the  narrowed  lower  end 
of  the  tube  is  warmed  a  little,  and  greased  with  tallow ;  a  caout- 
chouc tube,  about  30  mm.  long,  and  having  a  diameter  of  3  mm. 
in  the  clear,  is  then  drawn  over  it ;  into  the  other  end  of  this 
is  inserted  a  tube  of  pretty  thick  glass,  about  40  mm.  long,  and 
drawn  out  to  a  tolerably  fine  point;  it  is  advisable  to  slightly 
widen  the  upper  end  of  this 
tube  also,  and  to  cover  it  with 
a  thin  coat  of  tallow  ;  and  also 
to  tie  linen-thread,  or  twine, 
round  both  ends  of  the  con- 
nector, to  insure  perfect  tight- 
ness. 

The    space    between    the 

lower  orifice  of  the  burette  and  the  upper  orifice  of  the  small  de- 
livery tube  should  be  about  15  mm.  The  India  rubber  tube  is 
now  pressed  together  between  the  ends  of  the  tubes  by  the  com- 
pression-cock (or  clip).  This  latter  instrument  is  usually  made 
outof  brass  wire;  the  form  represented  in  fig.  8  was  given  by 
Mo  HE. 

A  good  clip  must  pinch  so  tight  that  not  a  particle  of  fluid  can 
make  its  way  through  the  connector  when  compressed  by  it ;  it 
must  be  so  const racted  that  the  analyst  may  work  it  with  perfect 
facility  and  exactness,  so  as  to  regulate  the  outflow  of  the  liquid 
with  the  most  rigorous  accuracy,  by  bringing  a  higher  or  less 
degree  of  pressure  to  bear  upon  it. 


38  OPERATIONS.  [§  21. 

For  supporting  MOHR'S  burettes,  I  use  the  holder  represented 
in  tig.  7 ;  this  instrument,  whilst  securely  confining  the  tube,  per- 
mits its  being  moved  up  and  down  with  perfect  freedom,  and  also 
its  being  taken  out,  without  interfering  with  the  compression-cock. 
The  position  of  the  burette  must  be  strictly  perpendicular,  to 
insure  which,  care  must  be  taken  to  have  the  grooves  of  the  cork 
lining,  which  are  intended  to  receive  the  tube,  perfectly  vertical, 
with  the  lower  board  of  the  stand  in  a  horizontal  position. 

To  charge  the  burette  for  a  volumetrical  operation,  the  point 
of  the  instrument  is  immersed  in  the  liquid,  the  compression-cock 
opened,  and  a  little  liquid,  sufficient  at  least  to  reach  into  the 
burette  tube,  sucked  up  by  applying  the  mouth  to  the  upper  end ; 
the  cock  is  then  closed,  and  the  liquid  poured  into  the  burette ' 
until  it  reaches  up  to  a  little  above  the  top  mark.  The  burette 
having,  if  required,  been  duly  adjusted  in  the  proper  vertical  posi- 
tion, the  liquid  is  allowed  to  drop  out  to  the  exact  level  of  the  top 
mark.  The  instrument  is  now  ready  for  use.  When  as  much 
liquid  has  flowed  out  as  is  required  to  attain  the  desired  object, 
the  analyst,  before  proceeding  to  read  off  the  volume  used,  has  to 
wait  a  few  minutes,  to  give  the  particles  of  fluid  adhering  to  the 
sides  of  the  emptied  portion  of  the  tube  proper  time  to  run  down. 
This  is  an  indispensable  part  of  the  operation  in  accurate  measure- 
ments, since,  if  neglected,  an  experiment  in  which  the  standard 
liquid  in  the  burette  is  added  slowly  to  the  fluid  under  examina- 
tion (in  wThich,  accordingly,  the  minute  particles  of  fluid  adhering 
to  the  glass  have  proper  time  afforded  them  during  the  operation 
itself  to  run  down),  will,  of  course,  give  slightly  different  results 
from  those  arrived  at  in  another  experiment,  where  the  larger  por- 
tion of  the  standand  fluid  is  applied  rapidly,  and  the  last  few  drops 
alone  are  added  slowly. 

The  way  in  which  the  reading-off  is  effected,  is  a  matter  of 
great  importance  in  volumetric  analysis  ;  the  first  requisite  is  to 
bring  the  eye  to  a  level  with  the  top  of  the  fluid.  We  must  con- 
sequently settle  the  question — What  is  to  be  considered  the  top  ? 

If  you  hold  a  burette,  partly  filled  with  water,  between  the  eye 
and  a  strongly  illumined  wall,  the  surface  of  the  fluid  presents 
the  appearance  shown  in  fig.  10  ;  if  you  hold  close  behind  the  tube 
a  sheet  of  white  paper,  with  a  strong  light  falling  on  it,  the  sur- 
face of  the  fluid  presents  the  appearance  shown  in  fig.  9. 

In  the  one  as  well  as  in  the  other  case,  you  have  to  read  off  at 


§ 


MEASTJBING    OF    FLUIDS. 


39 


the  lower  border  of  the  dark  zone,  this  being  the  most  distinctly 
marked  line.  FR.  MOIIR  recommends  the  following  device  for 
reading-off : — Paste  on  a  sheet  of  very  white  paper  a  broad  strip  of 
black  paper,  and,  when  reading-off,  hold  this  close  behind  the 
burette,  in  a  position  to  place  the  border  line  between  white  and 
black  from  2  to  3  mm.  below  the  lower  border  of  the  dark  zone, 
as  -shown  in  fig.  11 ;  read-off  at  the  lower  border  of  the  dark 


zone. 


Great  care  must  be  taken  to  hold  the  paper  invariably  in  the 
same  position,  since,  if  it  be  held  lower  down,  the  lower  border  of 
the  black  sone  will  move  higher  up. 


Fig.  9. 


Fig.  10. 


Fig.  11. 


I  prefer  to  read-off  in  a  light  which  causes  the  appearance  rep- 
resented in  fig.  9. 

By  the  use  of  ERDMANN'S  float  *  all  uncertainties  in  reading-off 
may  be  avoided.  Fig.  12  represents  a  burette  thus  provided.  In 
this  case  we  always  read  off  the  degree  of  the  burette  which  coin- 
cideswith  the  circle  in  the  middle  of  the  float.  The  float  must  be- 
so  fitted  to  the  width  of  the  burette  that  when  placed  in' the  filled 
burette,  it  will,  on  allowing  the  fluid  to  run  out  gradually,  sink 
down  with  the  same  without  wavering,  and  when  it  has  been 
pressed  down  into  the  fluid  of  the  closed  burette,  it  will  slowly 
rise  again.  The  weight  of  the  float  must,  if  necessary,  be  so  regu- 


*  Journ.  f.  prakt.  Chem.  71,  194. 


40  OPERATIONS.  [§  22. 

lated  by  mercury  that  when  placed  in  the  filled  tube  it  may  cut 
the  fluid  with  its  top  uniformly  all  round.  A  further  important 
condition  of  the  float  is  that  its  axis  should  coincide  as  nearly  as  pos- 
sible with  that  of  the  burette  tube,  so  that  the  division-mark  on  the 
burette  may  be  always  parallel  with  the  circular 
line  on  the  float. 

The  correctness  of  the  graduation  of  a  burette 
is  tested  in  the  most  simple  way,  as  follows :  fill 
the  instrument  up  to  the  highest  division  with 
water  of  16°,  then  let  10  c.  c.  of  the  liquid 
flow  out  into  an  accurately  weighed  flask,  and 
weigh;  then  let  another  quantity  of  10  c.  c. 
flow  out,  and  weigh  again,  and  repeat  the  oper- 
ation until  the  contents  of  the  burette  are  ex- 
hausted. If  the  instrument  is  correctly  graduated,, 
every  10  c.  c.  of  water  of  16°  must  weigh  9*990 
grm.  Differences  up  to  0*010  grm.  may  be  dis- 
regarded, since  even  with  the  greatest  care  bestowed 
on  the  process  of  reading-off,  deviations  to  that 
extent  will  occur  in  repeated  measurements  of  the 
uppermost  10  c.  c.  of  one  and  the  same  burette. 
With  the  float-burettes  the  weighings  agree  much 
more  accurately,  and  the  differences  for  10  c.  c.  do 
not  exceed  0-002  grm. 

MOHR'S  burette  is  unquestionably  the  best  and 
most  convenient  instrument  of  the  kind,  and  ought 
to  be  employed  in  the  measurement  of  all  liquids  which  are  not 
injuriously  affected  by  contact  with  caoutchouc.  Of  the  standard 
solutions  used  at  present  in  volumetric  analysis,  that  of  perman- 
ganate of  potassa  alone  cannot  bear  contact  with  caoutchouc. 

§22. 
II.    Gay-Lussarfs  Burette. 

Fig.  13  represents  this  instrument  in,  as  I  believe,  its  most 
practical  form. 

I  make  use  of  two  sizes,  one  of  50  c.  c.  divided  into  %  c.  c.> 
the  other  of  30  c.  c.  divided  into  -^  c.  c.  The  former  is  about 
33  cm.  long ;  the  graduated  portion  occupies  about  25  cm.;  the 
internal  diameter  of  the  wide  tube  measures  15  mm. ;  that  of 


§   23.]  MEASURING    OF    FLUIDS.  41 

the  narrow  tube  4  mm.,  which  in  the  upper  bent  end  gradually 
decreases  to  2  mm.  The  graduated  portion  of  the  smaller 
burette  is  about  28  cm.  long,  and  has  accordingly  an  internal 
diameter  of  about  11  mm. 

The  stand  which  I  make  use  of  to  rest  my  burettes  in,  consists 
of  a  disk  of  solid  wood,  from  5  to  6  cm.  high,  and 
from  10  to  12  cm.  in  diameter,  with  holes  made  with 
the  auger  and  chisel,  of  proper  size  to  receive  the  bot- 
tom part  of  the  burettes. 

To  complete  the  instrument,  MOHK  suggests  the 
use  of  a  perforated  cork,  bearing  a  short  glass  tube 
bent  at  aright  angle.  The  cork  being  inserted  into 
the  mouth  of  the  wide  tube,  a  piece  of  caoutchouc  is 
drawn  over  the  short  glass  tube ;  by  blowing  into  this 
with  greater  or  less  force,  the  outflow  of  the  liquid 
from  the  spout  of  the  slightly  slanting  burette  may 
be  regulated  at  pleasure. 

The   reading-off   of   the   height   of   the   liquid  is 
effected    in    the    same   way   as    explained   in    §  21. 
I  prefer,  however,  placing  the  burette  firmly  against 
a  perpendicular  partition,  either  a  strongly  illumined 
door,  or  the  pane  of  a  window,  to  insure  the  vertical 
position  of  the  instrument.     It  is  only  when   opera-        IflfiSSO 
ting  with  more  highly  concentrated,  and  accordingly 
opaque  solutions  of  permanganate  of  potassa,  that  the 
method  of  reading-off  requires  modification ;    in  that 
case,  the  upper  border  of  the  liquid  is  noted  ;  and  the  best  way  is 
to  place  the  burette  against  a  white  background,  and  read  off  by 
reflected  light. 

§23. 
III.   Geissler^s  Burette. 

In  this  instrument,  which  is  represented  in  fig.  14,  the  narrow 
tube  is  placed  inside  the  wide  tube  instead  of  outside,  as  in  GAY- 
LUSSAC'S  burette.  The  part  of  the  inner  tube  projecting  beyond 
the  wide  tube  is  thick  in  the  glass  ;  whilst  the  part  inside,  which 
is  of  the  same  inside  width,  is  made  of  very  thin  glass. 
.  This  is  a  very  convenient  instrument,  and  less  liable  to  frac- 
ture than  GAY-LUSSAC'S  burette. 


OPERATIONS. 


[§  24. 


II.  PRELIMINARY  OPERATIONS.  —  PREPARATION  OF  SUBSTANCES  FOR 
THE  PROCESSES  OF  QUANTITATIVE  ANALYSIS. 


1.  THE  SELECTION  OF  THE  SAMPLE. 

Before  the  analyst  proceeds  to  make  the  quantitative  analysis 
of  a  body,  he  cannot  too  carefully  consider 
whether  the  desired  result  is  fully  attained  if  lie 
simply  knows  the  respective  quantity  of  every 
individual  constituent  of  that  body.  This  pri- 
mary point  is  but  too  frequently  disregarded,  and 
thus  false  impressions  are  made,  even  by  the 
most  careful  analysis.  This  remark  applies  both 
to  scientific  and  to  technical  investigations. 

Therefore,  if  you  have  to  determine  the 
constitution  of  a  mineral,  take  the  greatest  pos- 
sible care  to  remove  in  the  first  place  every 
particle  of  gangue,  and  disseminated  impuri- 
ties ;  remove  any  adherent  matter  by  wiping  or 
washing,  then  wrap  the  substance  up  in  a  sheet 
of  thick  paper,  and  crush  it  to  pieces  on  a  steel 
anvil  ;  and  pick  out  with  a  pair  of  small  pincers 
the  cleanest  pieces.  Crystalline  substances, 
prepared  artificially,  ought  to  be  purified  by  re- 
crystallization  ;  precipitates  by  thorough  wash- 
ing, &c.,  &c. 

In  technical  investigations,  —  when  called 
upon,  for  instance,  to  determine  the  amount  of 
peroxide  presentin  a  manganese  ore,  or  the 
amount  of  iron  present  in  an  iron  ore,  —  the  first 
point  for  consideration  ought  to  be  whether  the 
samples  selected  correspond  as  much  as  possible 
to  the  average  quality  of  the  ore.  What  would 
it  serve,  indeed,  to  the  purchaser  of  a  manganese 
mine  to  know  the  amount  of  peroxide  present 
In  a  "select,  possibly  particularly  rich,  sample  ? 

These  few  observations  will  suffice  to  show  that  no  universally 
applicable  and  valid  rules  to  guide  the  analyst  in  the  selection  of 
the  sample  can  be  laid  down  ;  he  must  in  every  individual  case, 


Fig.  14. 


§  25.]  MECHANICAL    DIVISION.  43 

on  the  one  hand,  examine  the  substance  carefully,  and  more  par- 
ticularly also  under  the  microscope,  or  through  a  lens  ;  and,  on  the 
other  hand,  keep  clearly  in  view  the  object  of  the  investigation, 
and  then  take  his  measures  accordingly. 

§  25. 
2.  MECHANICAL  DIVISION. 

In  order  to  prepare  a  substance  for  analysis,  i.e.,  to  render  it 
accessible  to  the  action  of  solvents  or  fluxes,  it  is  generally  indis- 
pensable, in  the  first  place,  to  divide  it  into  minute  parts,  since 
this  will  create  abundant  points  of  contact  for  the  solvent,  and 
will  counteract,  and,  as  far  as  practicable,  remove  the  adverse 
influences  of  the  power  of  cohesion,  thus  fulfilling  all  the  condi- 
tions necessary  to  effect  a  complete  and  speedy  solution. 

The  means  employed  to  attain  this  object  vary  according  to  the 
nature  of  the  different  bodies  we  have  to  operate  upon.  In  many- 
cases,  simple  crushing  or  pounding  is  sufficient ;  in  other  cases  it 
is  necessary  to  reduce  the  powder  to  the  very  highest  degree  of 
fineness,  by  sifting  or  by  elutriation. 

The  operation  of  powdering  is  conducted  in  mortars ;  the  first 
and  most  indispensable  condition  is,  that  the  material  of  the  mor- 
tar be  considerably  harder  than  the  substance  to  be  pulverized,  so 
as  to  prevent,  as  far  as  practicable,  the  latter  from  being  contami- 
nated with  any  particles  of  the  former.  Thus,  for  pounding  salts 
and  other  substances  possessing  no  very  considerable  degree  of 
hardness,  porcelain  mortars  may  be  used,  whilst  the  pounding  of 
harder  substances  (of  most  minerals,  for  instance,)  requires  vessels 
of  agate,  chalcedony,  or  flint.  In  such  cases,  the  larger  pieces  are 
first  reduced  to  a  coarse  powder ;  this  is  best  effected  by  wrapping 
them  up  in  several  sheets  of  writing-paper,  and  striking  them  with 
a  hammer  upon  a  steel  or  iron  plate ;  the  coarse  powder  thus 
obtained  is  then  pulverized,  in  small  portions  at  a  time,  in  an  agate 
mortar,  until  it  is  reduced  to  the  state  of  an  impalpable  powder. 
If  we  have  but  a  small  portion  of  a  mineral  to  operate  upon,  and 
indeed  in  all  cases  where  we  are  desirous  of  avoiding  loss,  it  is 
advisable  to  use  a  steel  mortar  (fig.  15)  for  the  preparatory  reduc- 
tion of  the  mineral  to  coarse  powder. 

ab  and  cd  represent  the  two  parts  of  the  mortar ;  these  may  1  >e 
readilv  taken  asunder.  The  substance  to  be  crushed  (having,  if 


44  OPERATIONS.  [§  25. 

practicable,  -first  been  broken  into  small  pieces),  is  placed  in  the 
cylindrical  chamber  ef ;  the  steel  cylinder,  which  fits  somewhat 
loosely  into  the  chamber,  serves  as  pestle.  The  mortar  is  placed 
upon  a  solid  support,  and  perpendicular  blows  are  repeatedly 

struck  upon  the  pestle  with  a  hammer 
until  the  object  in  view  is  attained. 

Minerals  which  are  very  difficult 
to  pulverize  should  be  strongly  ignited, 
and  then  suddenly  plunged  into  cold 
water,  and  subsequently  again  ignited. 
This  process  is  of  course  applicable  only 
to  minerals  which  lose  no  essential  con- 
stituent on  ignition,  and  are  perfectly 
insoluble  in  water. 

In  the  purchase  of  agate  mortars, 
especial  care  ought  to  be  taken  that  they 
have  no  palpable  cracks  or  indentations ; 
very  slight  cracks,  however,  that  cannot 

be  felt,  do  not  render  the  mortar  useless,  although  they  impair  its 
durability. 

Minerals  insoluble  in  acids,  and  which  consequently  require 
fusing,  must  especially  be  finely  divided,  otherwise  we  cannot  calcu- 
late upon  complete  decomposition.  This  object  may  be  obtained 
either  by  triturating  the  pounded  mineral  with  water,  or  by  elutri- 
ation,  or  by  sifting;  the  two  former  processes,  however,  can  be 
resorted  to  only  in  the  case  of  substances  which  are  not  attacked 
by  water.  It  is  quite  clear  that  analysts  must  in  future  be  much 
more  cautious  in  this  point  than  has  hitherto  been  the  case,  since 
we  know  now  that  many  substances  which  are  usually  held  to  be 
insoluble  in  water  are,  when  in  a  state  of  minute  division,  strongly 
affected  by  that  solvent;  thus,  for  instance,  water,  acting  upon 
some  sorts  of  finely  pulverized  glass,  is  found  to  rapidly  dissolve 
from  2  to  3  per  cent,  of  powder  even  in  the  cold.  (PELOUZE.*) 
Thus,  again,  finely  divided  feldspar,  granite,  trachyte  and  porphyry 
give  up  to  water  both  alkali  and  silica.  (H.  LuDwiG.f) 

Trituration  with  water  (levigation).  Add  a  little  water  to  the 
pounded  mineral  in  the  mortar,  and  triturate  the  paste  until  all 
crepitation  ceases,  or,  which  is  a  more  expeditious  process,  transfer 

*  Compt.  Rend.,  t.  xliii.  pp.  117-123.  f  Archiv  der  Pharm.  91,  147. 


§  25.]  MEASURING    OF    FLUIDS.  45 

the  mineral  paste  from  the  mortar  to  an  agate  or  flint  slab,  and  tritu- 
rate it  thereon  with  a  muller.  Rinse  the  paste  off,  with  the  wash- 
ing bottle,  into  a  smooth  porcelain  basin  of  hemispheric  form, 
evaporate  the  water  on  the  water-bath,  and  mix  the  residue  most 
carefully  with  the  pestle.  (The  paste  may  be  dried  also  in  the 
agate  mortar,  but  at  a  very  gentle  heat,  since  otherwise  the  mortar 
might  crack.) 

To  perform  the  process  of  elutriation^  the  pasty  mass,  having 
first  been  very  finely  triturated  with  water,  is  washed  off  into  a 
beaker,  and  stirred  with  distilled  water ;  the  mixture  is  then  allowed 
to  stand  a  minute  or  so,  after  which  the  supernatant  turbid  fluid  is 
poured  oif  into  another  beaker.  The  sediment,  which  contains  the 
coarser  parts,  is  then  again  subjected  to  the  process  of  trituration, 
etc.,  and  the  same  operation  repeated  until  the  whole  quantity  is 
elutriated.  The  turbid  fluid  is  allowed  to  stand  at  rest  until  the 
minute  particles  of  the  substance  held  in  suspension  have  subsided, 
which  generally  takes  many  hours.  The  water  is  then  finally 
decanted,  and  the  powder  dried  in  the  beaker. 

The  process  of  sifting  is  conducted  as  follows :  a  piece  of  fine, 
well-washed,  and  thoroughly  dry  linen  is  placed  over  the  mouth  of 
a  bottle  about  10  cm.  high,  and  pressed  down  a  little  into  the  mouth, 
so  as  to  form  a  kind  of  bag ;  a  portion  of  the  finely  triturated  sub- 
stance is  put  into  the  bag,  and  a  piece  of  soft  leather  stretched  tightly 
over  the  top  by  way  of  cover.  By  drumming  with  the  finger  on  the 
leather  cover,  a  shaking  motion  is  imparted  to  the  bag,  which 
makes  the  finer  particles  of  the  powder  gradually  pass  through  the 
linen.  The  portion  remaining  in  the  bag  is  subjected  again  to 
trituration  in  an  agate  mortar,  and,  together  with  a  fresh  portion 
of  the  powder,  sifted  again;  and  the  same  process  is  continued 
until  the  entire  mass  has  pass  through  the  bag  into  the  glass. 

When  operating  on  substances  consisting  of  different  com- 
pounds it  would  be  a  grave  error  indeed  to  use  for  analysis  the 
powder  resulting  from  the  first  process  of  elutriation  or  sifting, 
since  this  will  contain  the  more  readily  pulverizable  constituents  in 
a  greater  proportion  to  the  more  resisting  ones  than  is  the  case 
with  the  original  substance. 

Great  care  must,  therefore,  also  be  taken  to  avoid  a  loss  of 
substance  in  the  process  of  elutriation  or  sifting,  as  this  loss  is 
likely  to  be  distributed  unequally  among  the  several  component 
parts. 


46  OPERATIONS.  [§  26. 

In  cases  where  it  is  intended  to  ascertain  the  average  composi- 
tion of  a  heterogeneous  substance,  of  an  iron  ore  for  instance,  a 
large  average  sample  is  selected,  and  reduced  to  a  coarse  powder ; 
the  latter  is  thoroughly  intermixed,  a  portion  of  it  powdered  more 
finely,  and  mixed  uniformly,  and  finally  the  quantity  required  for 
analysis  is  reduced  to  the  finest  powder.  The  most  convenient 
instrument  for  the  crushing  and  coarse  pounding  of  large  samples 
of  ore,  &c.,  is  a  steel  anvil  and  hammer.  The  anvil  in  my  own 
laboratory  consists  of  a  wood  pillar,  85  cm.  high  and  26  cm.  in 
diameter,  into  which  a  steel  plate,  3  cm.  thick  and  20  cm.  in 
diameter,  is  let  to  the  depth  of  one-half  of  its  thickness.  A  brass 
ring,  5  cm.  high,  fits  round  the  upper  projecting  part  of  the  steel 
plate.  The  hammer,  which  is  well  steeled,  has  a  striking  surface 
of  5  cm.  diameter.  An.  anvil  and  hammer  of  this  kind  afford, 
among  others,  this  advantage,  that  their  steel  surfaces  admit  most 
readily  of  cleaning.  To  convert  the  coarse  powder  into  a  finer,  a 
smooth-turned  steel  mortar  of  about  130  mm.  upper  diameter  and 
74  mm.  deep  is  used — the  final  trituration  is  conducted  in  an  agate 
mortar. 

§26. 

3.  DRYING. 

Bodies  which  it  is  intended  to  analyze  quantitatively  must  be, 
when  weighed,  in  a  definite  state,  in  a  condition  in  which  they  can 
be  always  obtained  again. 

Now,  the  essential  constituents  of  a  substance  are  usually  accom- 
panied by  an  unessential  one,  viz.,  a  greater  or  less  amount  of 
water,  enclosed  either  within  its  lamellae,  or  adhering  to  it  from 
the  mode  of  its  preparation,  or  absorbed  by  it  from  the  atmosphere. 
It  is  perfectly  obvious  that  to  estimate  correctly  the  quantity  of  a 
substance,  we  must,  in  the  first  place,  remove  this  variable  amount 
of  water.  Most  solid  bodies,  therefore,  require  to  be  dried  before 
they  can  be  quantitatively  analyzed. 

The  operation  of  drying  is  of  the  very  highest  importance  for 
the  correctness  of  the  results  ;  indeed  it  may  safely  be  averred  that 
many  of  the  differences  observed  in  analytical  researches  proceed 
entirely  from  the  fact  that  substances  are  analyzed  in  different 
states  of  moisture. 

Many  bodies  contain,  as  is  well  known,  water  which  is  proper 


xj  26. J  DESICCATION.  47 

to  them  either  as  inherent  in  their  constitution  or  as  so-called  water 
of  crystallization.  In  contradistinction  to  this,  we  will  employ  the 
term  moisture  to  designate  that  variable  adherent  or  mechanically 
enclosed  water,  with  the  removal  of  which  the  operation  of  drying 
in  the  sense  here  in  view  is  alone  concerned. 

In  the  drying  of  substances  for  quantitative  analysis,  our  object 
is  to  remove  all  moisture,  without  interfering  in  the  slightest  degree 
with  combined  water  or  any  other  constituent  of  the  body.  To 
accomplish  this  object,  it  is  absolutely  requisite  that  we  should 
know  the  properties  which  the  substance  under  examination  mani- 
fests in  the  dry  state,  and  whether  it  loses  water  or  other  constitu- 
ents at  a  red  heat,  or  at  100°,  or  in  dried  air,  or  even  simply  in 
contact  with  the  atmosphere.  These  data  will  serve  to  guide  us  in 
the  selection  of  the  process  of  desiccation  best  suited  to  each  sub- 
stance.* 

The  following  classification  may  accordingly  be  adopted  : — 

a.  Xnl.Hftances  which  lose  water  even  in  simple  contact  with  the 
atitwxplu -re  ;  such  as  sodium  sulphate,  crystallized  sodium  carbon- 
ate, etc.  Substances  of  this  kind  turn  dull  and  opaque  when 
exposed  to  the  air,  and  finally  crumble  wholly  or  partially  to  a  white 
powder.  They  are  more  difficult  to  dry  than  many  other  bodies. 
The  process  best  adapted  for  the  purpose,  is  to  press  the  pulverized 
salts  with  some  degree  of  force  between  thick  layers  of  fine  white 
blotting-paper,  repeating  the  operation  with  fresh  paper  until  the 
last  sheets  remain  absolutely  dry. 

It  is  generally  advisable  in  the  course  of  this  operation  to  repow- 
der  the  salt. 

~b.  Substances  which  do  not  yield  water  to  the  atmosphere  (unless 
if  1$  perfectly  dry\  but  effloresce  in  art  (-fir  nil h/  tfried  air  •  such  as 
magnesium  sulphate,  sodium  potassium  tartrate  (Rochelle  salt),  etc. 
Salts  of  this  kind  are  reduced  to  powder,  which,  if  it  be  very 
moist,  is  pressed  between  sheets  of  blotting-paper,  as  in  a  •  after 
this  operation,  it  must  be  allowed  to  remain  for  some  time  spread 
in  a  thin  layer  upon  a  sheet  of  blotting-paper,  effectually  protected 
against  dust,  and  shielded  from  the  direct  rays  of  the  sun. 

*  The  dried  substance  should  always  at  once  be  transferred  to  a  well-closed 
vessel ;  glass  tubes,  sealed  at  one  end,  and  of  sufficiently  thick  glass  to  bear  the 
firm  insertion  of  tight-fitting  smooth  corks — weighing-tubes — are  usually  employed 
for  this  purpose. 


48 


OPERATIONS. 


[§27. 


c.  Substances  which  undergo  no  alteration  in  dried  air,  but  lose 
water  at  100° ;  calcium  tartrate,  for  instance.  These  are  finely 
pulverized  ;  the  powder  is  put  in  a  thin  layer  into  a  watch-glass  or 
shallow  dish,  and  the  latter  placed  inside  a  chamber  in  which  the 
air  is  kept  dry  by  means  of  sulphuric  aciol.  This  process  is  usually 
conducted  in  one  of  the  following  apparatuses,  which  are  termed 
desiccators,  and  subserve  still  another  purpose  besides  that  of  dry- 
ing, viz.,  that  of  allowing  hot  crucibles,  dishes,  etc.,  to  cool  in  dry 


air. 


In  fig.  16,  a  represents  a  glass  plate  (ground-glass  plates  answer 
the  purpose  best),  ~b,  a  bell  jar  with  ground  rim,  which  is  greased 
with  tallow  ;  c  is  a  glass  basin  with  sulphuric  acid ;  d,  a  round  iron 


Fig.  16. 


Fig.  17. 


plate,  supported  on  three  feet,  with  circular  holes  of  various  sizes, 
for  the  reception  of  the  watch-glasses,  crucibles,  etc.,  containing  the 
substance. 

In  fig.  17,  a  represents  a  beaker  with  ground  and  greased  rim, 
and  filled  to  one-fourth  or  one-third  with  concentrated  sulphuric 
acid ;  ~b  is  a  ground-glass  plate ;  c  is  a  bent  wire  of  lead,  which 
serves  to  support  the  watch-glass  containing  the  substance. 

Fig.  18  represents  a  readily  portable  desiccator,  used  more  par- 
ticularly to  receive  crucibles  in  course  of  cooling,  and  carry  them 
to  the  balance.  The  instrument  consists  of  a  box  made  of  strong 
glass ;  the  lid  must  be  ground  to  shut  air-tight ;  the  place  on  which 
it  joins  is  greased  with  tallow.  The  outer  diameter  of  my  boxes 


§28.] 


DESICCATION. 


49 


Fig.  18. 


is  105  mm. ;  the  sides  are  6  mm.  thick.  The  aperture  has  a  diam- 
eter of  80  mm. ;  the  box  up  to  the  small  part  is  65  mm.  high ;  the 
lid  has  the  same  height ;  the  small  part 
itself  is  15  mm.  high,  and  ground  to  a 
slightly  conical  shape.  A  brass  ring, 
with  rim,  fits  exactly  into  the  aperture ; 
the  rim  must  not  project  beyond  the 
glass.  The  ring  bears  a  triangle  of 
iron,  or,  better,  platinum  wire,  intended 
for  the  reception  of  crucibles,  &c. 

The  body  which  it  is  intended  to 
dry  is  kept  exposed  to  the  action  of 
the  dry  air  in  the  glass,  until  it  shows 
no  further  diminution  of  weight.  Sub- 
stances upon  which  the  oxygen  of  the 
air  exercises  a  modifying  influence  are 
dried  in  a  similar  manner,  under  the 
exhausted  receiver  of  an  air-pump. 
Substances  which,  though  losing  no 
water  in  dry  air,  yet  give  off  ammonia, 
are  dried  over  cuicklime,  mixed  with  some  chloride  of  ammonium 
in  powder,  and  consequently  in  an  anhydrous  ammoniacal  atmo- 
sphere. 

§28. 

d.  Substances  which  at  100°  completely  lose  their  moisture, 
without  suffering  any  other  alteration,  such  as  hydrogen  potas- 
sium tartrate,  sugar,  etc.  These  are  dried  in  the  water-bath ;  in 
the  case  of  slow-drying  substances,  or  where  it  is  wished  to  expe- 
dite the  operation,  with  the  aid  of  a  cur- 
rent of  dry  air. 

Fig.  19  represents  the  water-bath 
most  commonly  used.  It  is  made  of 
sheet  copper.  The  engraving  renders 
a  detailed  description  unnecessary.  The 
inner  chamber,  c,  is  surrounded  on  five 
sides  by  the  outer  case  or  jacket,  d  e, 
without  communicating  with  it.  The  Fi  19 

object  of  the  apertures  g  and  h  is  to  effect 
change  of  air,  which  purpose  they  answer  sufficiently  well.     When 


50  OPERATIONS.  [§    28. 

it  is  intended  to  use  the  apparatus,  the  outer  case  is  filled  to  about 
one-half  with  rain-water,  and  the  aperture  a  is  closed  with  a  perfor- 
ated cork,  into  which  a  glass  tube  is  fitted  ;  the  aperture  b  is  entirely 
closed.  If  the  apparatus  is  intended  to  be  heated  over  charcoal,  it 
should  have  a  length  of  about  20  cm.  from  d  to  f ;  but  if  over  a 
gas-,  spirit-,  or  oil-lamp,  it  should  be  only  about  13  cm.  long.  In 
the  former  case,  the  inner  chamber  is  17  cm.  deep,  14  cm.  broad, 
and  10  cm.  high ;  in  the  latter  case,  it  is  10  cm.  deep,  9  cm.  broadr 
and  6  cm.  high.  The  temperature  in  the  inner  chamber  never 
quite  reaches  100° ;  to  bring  it  up  to  100°,  F.  ROCHLEDEK  has  sug- 
gested to  close  I  with  a  double-limbed  tube,  the  outer  longer  limb 
of  which  dips  into  a  cylinder  filled  with  water;  a  is  in  that  case 
closed  with  a  perforated  cork  bearing  a  sufficiently  tall  funnel 
tube,  which  fits  air-tight  in  the  cork.  The  lower  end  of  this  tube 
reaches  down  to  one  inch  from  the  bottom. 

In  large  analytical  laboratories  water  is  usually  kept  boiling  all 
day  long,  for  the  production  of  distilled  water.  The  boilers  used 
in  my  own  laboratory  have  the  shape  of  somewhat  oblong  square 
boxes,  about  120  cm.  long,  60  cm.  broad,  and  24  cm.  high ;  the 
front  of  the  boiler  has  soldered  into  it,  one  above  the  other,  two 
rows  of  drying  chambers,  of  the  kind  shown  in  fig.  19.  This 
gives  so  many  ovens  that  almost  every  student  may  have  one  for 
his  special  use.  Most  of  these  ovens  are  from  11  to  12  cm.  deep 
and  broad,  and  8  cm.  high ;  some  of  them,  however,  are  16  cm. 
deep  and  broad,  to  enable  them  to  receive  large-sized  dishes.  The 
substances  to  be  dried  are  usually  put  on  double  watch-glasses, 
laid  one  within  the  other,  which  are  placed  in  the  oven,  and  the 
door  is  then  closed.  In  the  subsequent  process  of  weighing,  the 
upper  glassj  which  contains  the  substance,  is  covered  with  the 
lower  one.  The  glasses  must  be  -quite  cold  before  they  are  placed 

on  the  scale.  In  cases 
where  we  have  to  deal  with 
hygroscopic  substances,  the 
reabsorption  of  water  upon 
cooling  is  prevented  by  the 
selection  of  close-fitting 
glasses,  which  are  held 
tight  together  by  a  clasp 
(fig.  20),  and  allowed  to  cool  with  their  contents  under  a  bell- 
glass  over  sulphuric  acid  (see  fig.  16).  These  latter  instructions 


§28.] 


DESICCATION. 


51 


apply  equally  to  the  process  of  drying  conducted  in  other  appa- 
ratus. 

The  clasp  used  for  keeping  the  watch-glasses  pressed  together 
— and  which  in  all  cases  where  it  is  intended  to  ascertain  the  loss 
of  weight  which  a  substance  suffers  on  desiccation,  is  to  be  looked 
upon  as  belonging  to  the  glasses,  and  must  accordingly  be  weighed 
with  them — is  constructed  of  two  strips  of  thin  brass  plate,  about 
10  cm.  long,  and  1  cm.  wide,  which  are  laid  the  one  over  the 
other,  and  soldered  together  at  the  ends,  to  the  extent  of  5  to  6  mm. 

The  following  apparatus  (fig.  21)  serves  for  drying  substances 
in  a  current  of  air  : — 


21. 


a  represents  a  flask  filled  to  one-third  with  concentrated  sul- 
phuric acid ;  c  a  glass  vessel  (commonly  called  a  LIEBIG'S  drying- 
tube),  and  d  a  tin  vessel  provided  with  a  stop-cock  at  e,  and 
arranged  in  other  respects  as  the  cut  shows. 

A,  «,  represents  a  small  tin  vessel,  containing  water  and  covered 
with  a  lid ;  two  apertures  are  cut  into  the  border  of  the  latter,  to 
receive  the  ascending  limbs  of  c. 

The  tube  c  is  first  weighed  with  the  substance,  then  placed  in 
the  water-bath,  h,  i,  which  is  placed  over  a  spirit-  or  gas-lamp ; 
the  aspirator  d  is  then  filled  with  water,  and  c  connected  with  the 
flask  a  by  the  perforated  cork  g.  and  with  d  by  means  of  a  caout- 
chouc tube,/.  If  the  stop-cock  e  be  now  opened  so  as  to  cause  the 
water  to  drop  from  d,  the  air  will  pass  through  the  tube  £,  and 
after  being  dehydrated  by  the  sulphuric  acid,  will  pass  over  the 
heated  substance  in  c.  After  the  operation  has  been  continued 
for  some  time,  it  is  interrupted  for  the  purpose  of  weighing  the 


52 


OPERATIONS. 


[§29. 


tube  c  and  its  contents,  and  then  resumed  again,  and  continued 
until  the  weight  of  c  (and  its  contents)  remains  stationary.  The 
current  of  cold  air  exercising  its  constant  cooling  action  upon  the 
substance,  the  latter  never  really  reaches  100°.  It  is,  therefore, 
sometimes  advisable  to  substitute  for  the  water  in  the  bath  a  satu- 
rated solution  of  common  salt. 

With  this  substitution,  the  apparatus  represented  in  fig.  21 
will  be  found  to  effect  its  purpose  the  most  expeditiously.  It  is 
not  adapted,  however,  for  drying  such  substances  as  have  a  ten- 
dency to  fuse  or  agglutinate  at  100°. 


§29. 

e.  Substances  which  persistently  retain  moisture  at  100°,  or 
become  completely  dry  only  after  a  very  long  time  •  but  which  are 
decomposed  by  a  red  heat. 

t       The  desiccation  of  such  substances  is  effected  in  the  air-bath  or 
oil-bath,  the  temperature  being  raised  to  110-120°,  and  still  higher, 

and,  according  to  circumstances, 
with  or  without  application  of  a 
current  of  air,  carbon  dioxide, 
or  hydrogen. 

Figs.  22  and  23  represent  two 
air-baths  of  simple  construction  ; 
the  former  (fig.  22)  adapted  for 
the  desiccation  of  a  single  sub- 
stance, the  latter  suited  for  the 
simultaneous  drying  of  several 
substances. 

In  fig.  22,  A  is  a  box  of  strong 
sheet  copper,  about  11  cm.  high, 
and  9  cm.  in  diameter.  The  box 
is  closed  with  the  loose-fitting 
cover  B,  which  is  provided  with  a 
narrow  rim,  and  has  two  aper- 
tures, C  and  E ';  C  is  intended 
to  receive  the  thermometer  _Z>, 
which  is  fitted  into  it  by  a  per- 
forated cork,  ^affords  an  exit  to  the  aqueous  vapors,  and  is.  ac- 
cording to  circumstances,  either  left  open,  or  loosely  closed.  In 


§  29.]  DESICCATION.  53 

the  interior  of  the  box,  about  half-way  up,  are  fixed  three  pins, 
supporting  a  triangle  of  moderately  stout  wire,  upon  which  the 
crucible  with  the  substance  is  placed  uncovered.  The  bulb  of  the 
thermometer  approaches  the  crucible  as  closely  as  possible,  but 
without  touching  the  triangle.  The  heating  is  effected  by  means 
of  a  gas-  or  spirit-lamp.  When  the  apparatus  has  cooled  sufficient- 
ly to  aUow  its  being  laid  hold  of  without  inconvenience,  the  lid  i.s 
removed,  the  crucible,  which  is  still  warm,  taken  out,  covered,  and 
allowed  to  cool  in  a  desiccator ;  and  weighed  when  cold. 

In  fig.  23,  a  b  is  a  case  of  strong  sheet  copper,  with  riveted  or 
locked  joints,  of  a  width 
and  depth  of  15  to  20  cm., 
and  corresponding  height. 
The  aperture  c  is  intended 
to  receive  a  perforated 
cork,  into  which  is  fixed 
a  thermometer,  d,  which 
reaches  into  the  interior 
of  the  case ;  within  is  a 
shelf,  on  which  are  placed 
the  watch-glasses  with  the 
substances  to  be  dried. 
The  case  is  heated  by  means 
of  a  gas-,  spirit-,  or  oil-lamp. 
When  the  temperature  has 
once  reached  the  intended 
point,  it  is  easy  to  maintain 
it  pretty  constant,  by  regu- 


Fig.  28. 


lating  the  flame.*  In  order  to  limit  as  much  as  possible  the  cooling 
from  without,  it  is  advisable  to  put  over  the  whole  apparatus  a 
pasteboard  hood  with  a  movable  front. 

[The  air-bath,  fig.  23,  by  a  slight  alteration,  may  serve  for  de- 
siccating in  a  stream  of  dry  air.  For  this  purpose,  cut  a  circular 
orifice,  35  mm.  wide,  in  each  end  of  the  copper  chamber,  and  rivet 
over  each  orifice  a  copper  tube  or  ring  of  corresponding  diameter, 
and  25  mm.  long.  Fit  a  glass  tube  of  20  mm.  diameter,  by  means 
of  perforated  corks,  into  these  openings,  so  that  it  shall  traverse 
the  chamber  and  project  40-50  mm.  beyond  the  corks  at  each  end. 

*  With  a  gas-lamp,  Kemp's  regulator  improved  by  Bunsen,  may  advanta- 
geously be  used  to  obtain  constant  temperatures. 


54  OPERATIONS.  [§   30. 

The  copper  tubes  should  be  so  adjusted  that  the  glass  tube  shall 
stand  horizontally  in  the  chamber,  at  the  same  height  as  the  ther- 
mometer bulb  and  just  behind  it.  To  produce  the  current  of  dry 
air  one  of  the  projecting  ends  of  the  wide  tube  is  connected  by  a 
narrow  glass  tube  and  perforated  cork,  with  an  aspirator  as  in  fig. 
21,  the  other  with  a  large  calcium  chloride  tube ;  the  water  of  the 
aspirator  is  allowed  to  run  off  somewhat  rapidly  at  first,  more 
slowly  afterwards.  The  end  of  the  tube  that  delivers  the  air  into 
the  wide  tube  is  recurved,  so  that  the  substance  within  shall  not 
be  carried  away  in  the  current. 

The  substance  to  be  dried  is  weighed  out  in  a  tray  of  platinum 
or  porcelain,  fig.  24,  which  is  pushed  within  the  wide  glass  tube 

by  help  of  a  wire.  When  the  sub- 
stance is  hygroscopic,  the  tray  is 
placed  horizontally  within  a  test- 
tube,  which  is  corked  while  the 

weight  is  being  ascertained.  The  substance  and  tray,  after  drying, 
may  be  cooled  in  the  same  test-tube  ;  in  that  case  just  before  put- 
ting on  the  balance,  the  cork  should  be  removed  momentarily  to 
allow  the  tube  to  fill  with  air.] 

§30. 

The  copper  apparatus  represented  in  fig.  19,  when  made  with 
brazed  joints,  can  be  employed  also  as  a  paraffin e-bath  ;  wrhen  used 
for  that  purpose,  the  outer  case  is  tilled  to  two-thirds  with  par- 
affine.  To  note  the  temperature,  a  thermometer  is  inserted,  by 
means  of  a  perforated  cork,  in  the  aperture  a ;  with  the  bulb 
reaching  nearly  to  the  bottom,  or,  at  all  events,  entirely  immersed 
in  the  paraifine. 

Many  organic  substances,  when  dried  at  a  somewhat  high  tem- 
perature, suffer  alteration  by  the  action  of  the  atmospheric  oxygen. 
In  the  desiccation  of  such  substances,  oxygen  must  accordingly  be 
excluded. 

[The  drying  of  such  bodies  is  conducted  as  just  described  in 
the  modified  air-bath,  but  in  a  stream  of  dried  and  purified  hydro- 
gen or  carbonic  acid  (see  §  29).  The  gas  is  evolved  from  a  self- 
regulating  generator  (see  fig.  50),  §  108. 


§§  31,  32.]  DESICCATION.  o:> 

§31. 

f.  Substances  which  suffer  no  alteration  at  a  red  heat,  such  as 
barium  sulphate,  pearlash,  etc.,  are  very  readily  freed  from  mois- 
ture. They  need  simply  be  heated  in  a  platinum  or  porcelain 
crucible  over  a  gas  or  spirit-lamp  until  the  desired  end  is  attained. 
The  crucible,  having  first  been  allowed  to  cool  a  little,  is  put,  still 
hot,  under  a  desiccator,  and  finally  weighed  when  cold. 

III.  GENERAL  PROCEDURE  IN  QUANTITATIVE  ANALYSES. 

§32. 

It  is  important,  in  the  first  place,  to  observe  that  we  embrace 
in  the  following  general  analytical  method  only  the  separation  and 
determination  of  the  metals  and  their  combinations  with  the 
metalloids,  and  of  the  inorganic  acids  and  salts.  With  respect  to 
the  quantitative  analysis  of  other  compounds,  it  is  not  easy  to  lay 
down  a  universally  applicable  method,  except  that  their  constitu- 
ents usually  require  to  be  converted  first  into  acids  or  bases,  before 
their  separation  and  estimation  can  be  attempted ;  this  is  the  case, 
for  instance,  with  phosphorus  sulphide,  sulphur  chloride,  iodine 
chloride,  nitrogen  sulphide,  &c. 

The  quantitative  analysis  of  a  substance  presupposes  an  accurate 
knowledge  of  the  properties  of  the  same,  and  of  the  nature  of  its 
several  constituents.  These  data  will  enable  the  operator  at  once 
to  decide  whether  the  direct  estimation  of  each  individual  constitu- 
ent is  necessary  ;  whether  he  need  operate  only  on  one  portion 
of  the  substance,  or  whether  it  would  be  advantageous  to  deter- 
mine each  constituent  in  different  portions.  Let  us  suppose,  for 
instance,  we  have  a  mixture  of  sodium  chloride  and  anhydrous 
sodium  sulphate,  and  wish  to  ascertain  the  proportion  in  which 
these  two  substances  are  mixed.  Here  it  would  be  superfluous  to 
determine  each  constituent  directly,  since  the  determination  either 
of  the  quantity  of  the  chlorine,  or  of  the  sulphuric  acid,  is  quite 
sufficient  to  answer  the  purpose ;  still  the  estimation  of  both  the 
chlorine  and  the  sulphur  trioxide  will  afford  us  an  infallible  con- 
trol for  the  correctness  of  our  analysis ;  since  the  united  weights 
of  these  two  substances,  added  to  the  sodium  and  soda  respectively 
equivalent  to  them,  must  be  equal  to  the  weight  of  the  substance 
taken. 


56  OPERATIONS.  [§   33. 

These  estimations  may  be  made,  either  in  one  and  the  same 
portion  of  the  mixture,  by  first  precipitating  the  sulphuric  acid 
with  barium  nitrate,  and  subsequently  the  hydrochloric  acid  from 
the  filtrate  with  solution  of  silver  nitrate  ;  or  a  separate  portion  of 
the  mixture  may  be  appropriated  to  each  of  these  two  operations. 
Unless  there  is  some  objection  to  its  use  (e.g.,  deficiency  or  hetero- 
geneousness  of  substance),  the  latter  method  is  more  convenient 
and  generally  yields  more  accurate  results  ;  since,  in  the  former 
method,  the  unavoidable  washing  of  the  first  precipitate  swells  the 
amount  of  liquid  so  considerably  that  the  analysis  is  thereby 
delayed,  and,  moreover,  loss  of  substance  less  easily  guarded 
against. 

Before  beginning  all  analyses,  at  least  those  of  a  more  complex 
nature,  the  student  should  write  out  an  exact  plan,  and  accurately 
note  on  paper,  during  the  entire  process,  everything  that  he  does. 
It  is  in  the  highest  degree  unwise  to  rely  on  the  memory  in  a  com- 
plicated analysis.  When  students,  who  imagine  they  can  do  so, 
come,  a  week  or  a  fortnight  after  they  have  begun  their  analysis, 
to  work  out  the  results,  they  find  generally  too  late  that  they  have 
forgotten  much,  which  now  appears  to  them  of  importance  to 
know.  The  intelligent  pursuit  of  chemical  analysis  consists  in  the 
projecting  and  accurate  testing  of  the  plan  ;  acuteness  and  the 
power  of  passing  in  review  all  the  influencing  chemical  relations 
must  here  support  each  other.  He  who  works  without  a  thor- 
oughly thought-out  plan,  has  no  right  to  say  he  is  practising  chem- 
istry ;  for  a  mere  unthinking  stringing  together  of  a  series  of  filtra- 
tions,  evaporations,  ignitions,  and  weighings,  howsoever  well  these 
several  operations  may  be  performed,  is  not  chemistry. 

We  will  now  proceed  to  describe  the  various  operations  consti- 
tuting the  process  of  quantitative  analysis. 

§  33. 
1.  WEIGHING  THE  SUBSTANCE. 

The  amount  of  matter  required  for  the  quantitative  analysis  of  a 
substance  depends  upon  the  nature  of  its  constituents ;  it  is,  there- 
fore, impossible  to  lay  down  rules  for  guidance  on  this  point. 
Half  a  gramme  of  sodium  chloride,  and  even  less,  is  sufficient  to 
effect  the  estimation  of  the  chlorine.  For  the  quantitative  analy- 
sis of  a  mixture  of  common  salt  and  anhydrous  sodium  sulphate,  1 


§  34.]  ESTIMATION   OF   WATER!  57 

gramme  will  suffice  ;  whereas,  in  the  case  of  ashes  of  plants,  com- 
plex minerals,  &c.,  3  or  4  grammes,  and  even  more,  are  required. 
1  to  3  grm.  can  therefore  be  indicated  as  the  average  quantity 
suitable  in  most  cases.  For  the  estimation  of  constituents  present 
in  very  minute  proportions  only,  as,  for  instance,  sodium  and 
potassium  in  limestones,  phosphorus  or  sulphur  in  cast-iron,  &c., 
much  greater  quantities  are  often  required — 10,  20,  or  50  grammes. 

The  greater  the  amount  of  substance  taken  the  more  accurate 
will  be  the  analysis  ;  the  smaller  the  quantity,  the  sooner,  as  a  rule, 
will  the  analysis  be  finished.  We  would  advise  the  student  to 
endeavor  to  combine  accuracy  with  economy  of  time.  The  less 
substance  he  takes  to  operate  upon,  the  more  carefully  he  ought  to 
weigh ;  the  larger  the  amount  of  substance,  the  less  harm  can 
result  from  slight  inaccuracies  in  weighing.  Somewhat  large 
quantities  of  substance  are  generally  weighed  to  1  milligramme  ; 
minute  quantities,  to  y1^  of  a  milligramme. 

If  one  portion  of  a  substance  is  to  be  weighed  off,  we  first 
weigh  two  watch-glasses  which  fit  on  each  other,  or  else  an  empty 
platinum  crucible  with  lid,  then  we  put  some  substance  in,  and 
weigh  again  ;  the  difference  between  the  two  weighings  gives  the 
weight  of  the  substance  taken. 

If  several  quantities  of  a  substance  are  to  be  operated  upon, 
the  best  way  is  to  weigh  off  the  several  portions  successively ; 
which  may  be  accomplished  most  readily  by  weighing  in  a  glass 
tube,  or  other  appropriate  vessel,  the  whole  amount  of  substance, 
and  then  shaking  out  of  the  tube  the  quantities  required  one 
after  another  into  appropriate  vessels,  weighing  the  tube  after  each 
time. 

The  work  may  often  also  be  materially  lightened,  by  weighing 
off  a  larger  portion  of  the  substance,  dissolving  this  to  £,  -J  or  1 
litre,  and  taking  out  for  the  several  estimations  aliquot  parts,  with 
the  50  or  100  c.c.  pipette.  The  first  and  most  essential  condition 
of  this  proceeding,  of  course,  is  that  the  pipettes  must  accurately 
correspond  with  the  measuring  flasks  (§§  18  and  20). 

§34. 
2.  ESTIMATION  OF  THE  WATER. 

If  the  substance  to  be  examined — after  having  been  freed  from 
moisture  by  a  suitable  drying  process  (§§  26-32) — contains  water, 


58  OPERATIONS.  [§   35. 

it  is  usual  to  begin  by  determining  the  amount  of  this  water.  This 
operation  is  generally  simple  ;  in  some  instances,  however,  it  has 
its  difficulties.  This  depends  upon  various  circumstances,  viz., 
whether  the  compounds  intended  for  analysis  yield  their  water 
readily  or  not ;  whether  they  can  bear  a  red  heat  without  suffering 
decomposition  ;  or  whether,  on  the  contrary,  they  give  off  other 
volatile  substances,  besides  water,  even  at  a  lower  temperature. 

The  correct  knowledge  of  the  constitution  of  a  compound 
depends  frequently  upon  the  accurate  estimation  of  the  water  con- 
tained in  it ;  in  many  cases — for  instance,  in  the  analysis  of  the 
salts  of  known  acids — the  estimation  of  the  water  contained  in  the 
analyzed  compound  suffices  to  enable  us  to  deduce  the  formula. 
The  estimation  of  the  water  contained  in  a  substance  is,  therefore, 
one  of  the  most  important,  as  well  as  most  frequently  occurring 
operations  of  quantitative  analysis.  The  proportion  of  water  con- 
tained in  a  substance  may  be  determined  in  two  ways,  viz.,  a,  from 
the  diminution  of  weight  consequent  upon  the  expulsion  of  the 
water ;  &,  by  weighing  the  amount  of  water  expelled. 

§  35. 
a.  ESTIMATION  OF  THE  WATER  FROM  THE  Loss  OF  WEIGHT. 

This  method,  on  account  of  its  simplicity,  is  most  frequently 
employed.  The  modus  operandi  depends  upon  the  nature  of  the 
substance  under  examination. 

a.  The  substance  hears  ignition  without  losing  other  Constituents 
hesides  Water,  and  without  absorbing  Oxygen. 

The  substance  is  weighed  in  a  platinum  or  porcelain  crucible, 
and  placed  over  the  gas-  or  spirit-lamp  ;  the  heat  should  be  very 
gentle  at  first,  and  gradually  increased.  When  the  crucible  has 
been  maintained  some  time  at  a  red  heat,  it  is  allowed  to  cool  a 
little,  put  still  warm  under  the  desiccator,  and  finally  weighed  when 
cold.  The  ignition  is  then  repeated,  and  the  weight  again  ascer- 
tained. If  no  further  diminution  of  wreight  has  taken  place,  the 
process  is  at  at  end,  the  desired  object  being  fully  attained.  But 
if  the  weight  is  less  than  after  the  first  heating,  the  operation  must 
be  repeated  until  the  weight  remains  constant. 

In  the  case  of  silicates,  the  heat  must  be  raised  to  a  very  high 


g    35.]  ESTIMATION    OF    WATER.  59 

degree,  since  many  of  them  (e.g.  talc,  steatite,  nephrite)  only  begin 
at  a  red  heat  to  give  off  water,  and  require  a  yellow  heat  for  the 
complete  expulsion  of  that  constituent.  (Tn.  SCHEERER.*)  Such 
bodies  are  therefore  ignited  over  a  blast-lamp. 

In  the  case  of  substances  that  have  a  tendency  to  puff  off,  or  to 
spirt,  a  small  flask  or  retort  may  sometimes  be  advantageously  sub- 
stituted for  the  crucible.  Care  must  be  taken  to  remove  the  last 
traces  of  aqueous  vapor  from  the  vessel,  by  suction  through  a  glass 
tube. 

Decrepitating  salts  (sodium  chloride,  for  instance)  are  put- 
finely  pulverized,  if  possible  —  in  a  small  covered  platinum  crucible, 
which  is  then  placed  in  a  large  one,  also  covered  ;  the  whole  is 
weighed,  then  heated,  gently  at  iirst  for  some  time,  then  more 
strongly  ;  finally,  after  cooling,  weighed  agaiu. 

/3.  The    substance   loses  on    ignition    other    Constituents  besides 
Water  (Boracic  Acid,  Sulphuric  Acid,  Silicon  Fluoride,  dkc.). 

Here  the  analyst  has  to  consider,  in  the  first  place,  whether  the 
water  may  not  be  expelled  at  a  lower  degree  of  heat,  which  does 
not  involve  the  loss  of  other  constituents.  If  this  may  be  done, 
the  substance  is  heated  either  in  the  water-bath,  or  where  a  higher 
temperature  is  required,  in  the  air-bath  or  oil-bath,  the  tempera- 
ture being  regulated  by  the  thermometer.  The  expulsion  of  the 
water  may  be  promoted  by  the  co-operation  of  a  current  of  air 
(compare  §§  29  and  30)  ;  or  by  the  addition  of  pure  dry  sand  to 
the  substance,  to  keep  it  porous.f  The  process  must  be  continued 
under  these  circumstances  also,  until  the  weight  remains  constant. 

In  cases  where,  for  some  reason  or  other,  such  gentle  heating 
is  insufficient,  the  analyst  has  to  consider  whether  the  desired  end 
may  not  be  attained  at  a  red  heat,  by  adding  some  substance  that 
will  retain  the  volatile  constituent  whose  loss  is  apprehended. 
Thus,  for  instance,  the  crystallized  sulphate  of  alumina  loses  at  a 
red  heat,  besides  water,  also  sulphuric  acid  ;  now,  the  loss  of  the 
latter  constituent  may  be  guarded  against  by  adding  to  the  sul- 
phate an  excess  (about  six  times  the  quantity)  of  finely  pulverized, 
recently  ignited,  pure  lead  oxide.  But  the  addition  of  this  sub- 
stance will  not  prevent  the  escape  of  silicon  fluoride  from  silicates 
when  exposed  to  a  red  heat 


*  Jahresber.  von  Liebig  u.  Kopp,  1851,  610. 

f  Ann.  d.  Chem.  u.  Pharm.  53,  233.        \  Ibid.  81,  189. 


60  OPERATIONS. 

Thus  again,  the  amount  of  water  in  commercial  iodine  may  be 
determined  by'  triturating  the  iodine  together  with  eight  times  the 
quantity  of  mercury,  and  drying  the  mixture  at  100°  (BOLLEY*). 

y.  The  substance  contains  several  differently  combined  quantities 
of  Water  which  require  different  Degrees  of  Temperature 
for  Expulsion. 

Substances  of  this  nature  are  heated  first  in  the  water-bath, 
until  their  weight  remains  constant ;  they  are  then  exposed  in  the 
oil-  or  air-bath  to  150°,  200°,  or  250°,  &c.,  and  finally,  when  prac- 
ticable, ignited  over  a  gas-  or  spirit-lamp.  [In  such  experiments, 
it  is  best  to  proceed  as  described,  §  29,  p.  53,  viz.,  to  heat  in  a  cur- 
rent of  dried  air,  hydrogen,  or  carbon  dioxide.] 

In  this  manner  differently  combined  quantities  of  water  may 
be  distinguished,  and  their  respective  amounts  correctly  estimated. 
Thus,  for  instance,  crystallized  sulphate  of  copper  contains  28-87 
per  cent,  of  water,  which  escapes  at  a  temperature  below  140°,  and 
7*22  per  cent.,  which  escapes  only  at  a  temperature  between  220° 
and  260°. 

tf.  When  the  substance  has  a  tendency  to  absorb  oxygen  (from 
the  presence  of  ferrous  compounds,  for  instance)  the  water  is  bet- 
ter determined  in  the  direct  way,  than  by  the  loss.  (§  36.) 

§36. 
l>.  ESTIMATION  OF  WATER  BY  DIRECT  WEIGHING. 

This  method  is  resorted  to  by  way  of  control,  or  in  the  case  of 
substances  which,  upon  ignition,  lose,  besides  water,  other  con- 
stituents, which  cannot  be  retained  even  by  the  addition  of  some 
other  substance  (e.g.,  carbon  dioxide,  oxygen),  or  in  the  case  of 
substances  containing  bodies  inclined  to  oxidation  (e.g.,  ferrous 
compounds).  The  principle  of  the  method  is  to  expel  the  water 
by  the  application  of  a  red  heat,  so  as  to  admit  of  the  condensa- 
tion of  the  aqueous  vapor,  and  the  collection  of  the  condensed 
water  in  an  appropriate  apparatus,  partly  physically,  partly  by  the 
agency  of  some  hygroscopic  substance.  The  increase  in  the  weight 
of  this  apparatus  represents  the  quantity  of  the  water  expelled. 

The  operation  may  be  conducted  in  various  ways  ;  the  follow- 
ing is  one  of  the  most  appropriate  : — 

*Dingler's  Polyt.  Journ.,  126,  39. 


36.] 


ESTIMATION    OF    AVATEK. 


61 


B,  fig.  25  represents  a  gasometer  filled  with  air ;  b  a  flask  half- 
filled  with  concentrated  sulphuric  acid;  c  and  a  oare  calcium  chlo- 
ride tubes ;  d  is  a  bulb-tube. 


Fig.  25. 

The  substance  intended  for  examination  is  weighed  in  the  per 
fectlj  dry  tube  d*  which  is  then  connected  with  c  and  the 
weighed  calcium  chloride  tube  ao.  by  means  of  sound  and  well- 
dried  perforated  corks. 

The  operation  is  commenced  by  opening  the  stop-cock  of  the 
gasometer  a  little,  to  allow  the  air,  which  loses  all  its  moisture  in  ~b 
and  c,  to  pass  slowly  through  d ;  the  tube  d  is  then  heated  to  be- 
yond the  boiling-point  of  water,  by  holding  a  lamp  towards  f, 
taking  care  not  to  burn  the  cork ;  and  finally,  the  bulb  which  con- 
tains the  substance  is  exposed  to  a  low  red  heat,  the  temperature 
at/  being  maintained  all  the  while  at  the  point  indicated.  When 
the  expulsion  of  the  water  has  been  accomplished,  a  slow  current 
of  air  is  still  kept  up  till  the  bulb-tube  is  cold ;  the  apparatus  is 
then  disconnected,  and  the  calcium  chloride  tube  ao,  weighed. 
The  increase  in  the  weight  of  this  tube  represents  the  quantity  of 
water  originally  present  in  the  substance  examined. 

*  [It  is  usually  better  to  weigh  off  the  substance  into  a  tray  or  boat  of  porce- 
lain or  platinum,  and  place  this  within  a  straight  tube  of  hard  glass  and  ignite 
by  means  of  a  tube  furnace.] 


OPERATIONS. 


§  36. j 


The  empty  bulb  #,  in  which  the  greater  portion  of  the  water 
collects,  has  not  only  for  its  object  to  prevent  the  liquefaction  of 
the  calcium  chloride,  but  enables  the  analyst  also  to  test  the  con- 
densed water  as  to  its  reaction  and  purity. 

The  apparatus  may,  of  course,  be  modified  in  various  ways ; 
thus,  the  chloride  of  calcium  tubes  may  be  U-shaped ;  a  U-tube, 
filled  with  pieces  of  pumice-stone  saturated  with  sulphuric  acid, 
may  be  substituted  for  the  flask  with  sulphuric  acid ;  and  the  gaso- 
meter may  be  replaced  by  an  aspirator  (fig.  21)  joined  to  o. 

The  expulsion  of  the  aqueous  vapor  from  the  tube  containing 
the  substance  under  examination,  into  the  calcium  chloride  tube, 
may  be  effected  also  by  other  means  than  a  current  of  air  sup- 
plied by  a  gasometer  or  aspirator ;  viz.,  the  substance  under  ex- 
amination may  be  heated  to  redness  in  a  perfectly  dry  tube,  to- 
gether with  lead  carbonate,  since  the  carbon  dioxide  escaping 
from  the  latter  at  a  red  heat,  serves  here  the  same  purpose  as  a 
stream  of  air.  This  method  is  principally  applied  in  cases  where 
it  is  desirable  to  retain  an  acid  which  otherwise  would  volatilize 
together  with  the  water ;  thus,  it  is  applied,  for  instance,  for 
the  direct  estimation  of  the  water  contained  in  acid  potassium 
sulphate. 


Fig.  26. 

Fig.  26.  represents  the  disposition  of  the  apparatus. 

a  1)  is  a  common  combustion  furnace  ;  cf  a  tube  filled  as  fol- 
lows:— from  c  to  d  with  lead  carbonate,*  from  d  to  e  the  substance 
intimately  mixed  with  lead  carbonate,  and  from  e  tof  pure  lead  car- 
bonate. The  calcium  chloride  tube  </,  being  accurately  weighed, 
is  connected  with  the  tube  cf,  by  means  of  a  well-dried  perfo- 
rated cork,/*. 

The  operation  is  commenced  by  surrounding  the  tube  with  red- 

*  The  lead  carbonate  must  have  been  previously  ignited  to  incipient  decom- 
position, and  cooled  in  a  closed  tube. 


§  37.]  SOLUTION.  63 

hot  charcoal,  advancing  from/*  toward  <?;  the  fore  part  of  the 
tube  which  protrudes  from  the  furnace  should  be  maintained  at  a 
degree  of  heat  which  barely  permits  the  operator  to  lay  hold  of  it 
with  his  fingers.  All  further  particulars  of  this  operation  will  be 
found  in  the  chapter  on  organic  elementary  analysis.  The  mix- 
ing is  performed  best  in  the  tube  with  a  wire.  The  tube  of  may 
be  short  and  moderately  narrow. 

The  volatilization  of  an  acid  cannot  in  all  cases  be  prevented 
by  lead  oxide;  thus,  for  instance,  we  could  not  determine  the 
water  in  crystallized  boracicacid  by  the  above  process.  This  could 
readily  be  done,  however,  by  igniting  the  acid  mixed  with  excess 
of  dry  sodium  carbonate  in  a  glass  tube  drawn  out  behind  in  the 
form  of  a  beak,  receiving  the  water  in  a  calcium  chloride  tube, 
and  transferring  the  final  residue  of  aqueous  vapor  into  the  Ca  Cla 
tube  by  suction,  after  the  point  of  the  beak  has  been  broken  off. 
(See  Organic  Analysis.) 

The  foregoing  methods  for  the  direct  estimation  of  water  do 
not,  however,  yet  embrace  all  cases  in  which  those  described 
in  §  35  are  inapplicable ;  since  they  can  be  employed  only  if  the 
substances  escaping  along  with  the  water  are  such  as  will  not 
wholly  or  partly  condense  in  the  calcium  chloride  tube  (or  in  a 
tube  containing  fused  potassa,  or  one  filled  with  pumice-stone  satu- 
rated with  sulphuric  acid,  which  might  be  used  instead).  Thus 
they  are  perfectly  well  adapted  for  determining  the  water  in  the 
basic  zinc  carbonate,  but  they  cannot  be  applied  to  determine  the 
water  in  sodium  ammonium  sulphate.  With  substances  like  the 
latter,  we  must  either  have  recourse  to  the  processes  of  organic 
elementary  analysis,  or  we  must  rest  satisfied  with  the  indirect 
estimation  of  the  water. 

§37. 
3.  SOLUTION  OF  SUBSTANCES. 

Before  pursuing  the  analytical  process  further,  it  is  in  most 
cases  necessary  to  obtain  a  solution  of  the  substance.  This  opera- 
tion is  simple  where  the  body  may  be  dissolved  by  direct  treat- 
ment with  water,  or  acids,  or  alkalies,  &c. ;  but  it  is  more  compli- 
cated in  cases  where  the  body  requires  fluxing  as  an  indispensable 
preliminary  to  solution. 

When  we  have  mixed  substances  to  operate  upon,  the  compo- 


64  OPERATIONS.  [§  38. 

nent  parts  of  which  behave  differently  with  solvents,  it  is  not  by 
any  means  necessary  to  dissolve  the  whole  substance  at  first ;  on 
the  contrary,  the  separation  may,  in  such  cases,  be  often  effected, 
in  the  most  simple  and  expeditious  manner,  by  the  solvents  them- 
selves. Thus,  for  instance,  a  mixture  of  potassium  nitrate,  calcium 
carbonate,  and  barium  sulphate  may  be  readily  arid  accurately 
analyzed  by  dissolving  out,  in  the  first  place,  the  potassium  nitrate 
with  water,  and  subsequently  the  calcium  carbonate  by  hydrochloric 
acid,  leaving  the  insoluble  barium  sulphate. 

§  38. 
a.  DIRECT  SOLUTION. 

The  direct  solution  of  substances  is  effected,  according  to  cir- 
cumstances, in  beakers,  flasks,  or  dishes,  and  may,  if  necessary,  be 
promoted  by  the  application  of  heat ;  for  which  purpose  the  water- 
bath  will  be  found  most  convenient.  In  cases  where  an  open  fire, 
or  the  sand-bath,  or  an  iron-plate  is  resorted  to,  the  analyst  must 
take  care  to  guard  against  actual  ebullition  of  the  fluid,  since  this 
would  render  a  loss  of  substance  from  spirting  almost  unavoidable, 
especially  in  cases  where  the  process  is  conducted  in  a  dish.  Fluids 
containing  a  sediment,  either  insoluble,  or,  at  least,  not  yet  dissolved, 
will,  when  heated  over  the  lamp,  often  bump  and  spirt  even  at 
temperatures  far  short  of  the  boiling-point. 

In  cases  where  the  solution  of  a  substance  is  attended  with 
evolution  of  gas,  the  process  is  conducted  in  a  flask,  placed  in  a 
sloping  position,  so  that  the  spirting  drops  may  be  thrown  against 
the  walls  of  the  vessel,  and  thus  secured  from  being  carried  off 
with  the  stream  of  the  evolved  gas  ;  or  it  may  be  conducted  in  a 
beaker,  covered  with  a  large-sized  watch-glass,  which,  after  the 
solution  is  effected,  and  the  gas  expelled  by  heating  on  the  water- 
bath,  must  be  thoroughly  rinsed  with  the  washing-bottle. 

In  cases  where  the  solution  has  to  be  effected  by  means  of  con- 
centrated volatile  acids  (hydrochloric  acid,  nitric  acid,  aqua  regia), 
the  operation  should  never  be  conducted  in  a  dish,  but  always  in  a 
flask  covered  with  a  watch-glass,  or  placed  in  a  slanting  position, 
and  the  application  of  too  high  a  temperature  must  be  avoided. 
The  operation  should  always  be  conducted  also  under  a  hood,  with 
proper  draught,  to  carry  off  the  escaping  acid  vapors.  In  my  own 
laboratory,  I  use  for  the  latter  purpose  the  following  simple  contriv- 


SOLUTION.  Go 

ance  :  a  leaden  pipe,  permanently  fixed  in  a  convenient  position, 
leads  from  the  working  table  through  the  wall  or  the  window- 
frame  into  the  open  air.  The  end  in  the  laboratory  is  connected 
with  one  of  the  mouths  of  a  two-necked  bottle  which  contains  a 
little  water.  The  other  month  of  the  bottle  is  closed  with  a  per- 
forated cork,  bearing  a  firmly-fixed  glass  tube  bent  at  a  right  angle  ; 
the  portion  of  the  tube  which  enters  the  bottle  must  not  dip  into 
the  water.  The  solution-flask  being  now  closed  with  a  perforated 
cork,  or  an  india-rubber  cap,  bearing  a  glass  tube,  connected  by 
means  of  india-rubber  with  the  bent  tube  in  the  double-necked 
bottle,  the  vapors  evolved  are  carried  out  of  the  laboratory  without 
the  least  inconvenience  to  the  operator ;  moreover,  no  receding  of 
fluid  upon  cooling  need  be  apprehended.  Instead  of  conveying 
the  vapors  away  through  a  tube  leading  into  the  open  air,  a  conical 
glass-tube  filled  with  pieces  of  broken  glass,  moistened  with  water 
or  solution  of  sodium  carbonate,  may  be  fixed  on  the  second  mouth 
of  the  double-necked  bottle.  I,  however,  prefer  the  other  method. 
In  some  cases,  it  is  advisable  also  to  conduct  the  escaping  vapors 
into  a  little  water,  and,  when  solution  has  been  effected,  make  the 
water  recede  by  withdrawing  the  lamp,  since  this  will,  at  the  same 
time,  serve  to  dilute  the  solution ;  care  must  be  taken,  however,  to 
guard  against  a  premature  receding  of  the  water  in  consequence  of 
an  accidental  cooling  of  the  solution  flask. 

It  is  often  necessary,  in  conducting  a  process  of  solution,  to 
guard  against  the  action  of  the  atmospheric  oxygen ;  in  such  c; 
a  slow  stream  of  carbon  dioxide  is  transmitted  through  the  solu- 
tion-flask ;  in  some  cases  it  is  sufficient  to  expel  the  air,  by  simply 
first  putting  a  little  hydrogen  sodium  carbonate  into  the  flask,  con- 
taining an  excess  of  acid,  before  introducing  the  substance. 

§  39. 
J.  SOLUTION,  PRECEDED  BY  FLUXING. 

Substances  insoluble  in  water,  acids,  or  aqueous  alkalies,  usually 
require  decomposition  by  fluxing,  to  prepare  them  for  analysis. 
Substances  of  this  kind  are  often  met  with  in  the  mineral  kingdom  ; 
most  silicates,  the  sulphates  of  the  alkali-earth  metals,  chrome  iron- 
stone, (fee.,  belong  to  this  class. 

The  object  and  general  features  of  the  process  of  fluxing  have 
already  been  treated  of  in  the  qualitative  part  of  the  present  work. 


66  OPERATIONS.  ['§§  40,  41. 

The  special  methods  of  conducting  this  important  operation  will 
be  described  hereafter  under  "  The  analysis  of  silicates,"  and  in 
the  proper  places ;  as  a  satisfactory  description  of  the  process,  with 
its  various  modifications,  cannot  well  be  given  without  entering 
more  minutely  into  the  particular  circumstances  of  the  several 
special  cases. 

Decomposition  by  fluxing  often  requires  a  higher  temperature 
than  is  attainable  with  a  spirit-lamp  with  double  draught,  or  with 
a  common  gas-lamp.  In  such  cases,  the  glass-blower's  lamp,  fed 
with  gas,  is  used  with  advantage. 

§  40. 

4.  CONVERSION  OF  THE  DISSOLVED  SUBSTANCE   INTO  A  WEIGHABLE 

FORM. 

The  conversion  of  a  substance  in  a  state  of  solution  into  a  form 
adapted  for  weighing  may  be  effected  either  by  evaporation  or  by 
precipitation.  The  former  of  these  operations  is  applicable  only 
in  cases  where  the  substance,  the  weight  of  which  we  are  desirous 
to  ascertain,  either  exists  already  in  the  solution  in  the  form  suit- 
able for  the  determination  of  its  weight,  or  may  be  converted  into 
such  form  by  evaporation  in  conjunction  with  some  reagent.  The 
solution  must,  moreover,  contain  the  substance  unmixed,  or,  at 
least,  mixed  only  with  such  bodies  as  are  expelled  by  evaporation 
or  at  a  red-heat.  Thus,  for  instance,  the  amount  of  sodium 
sulphate  present  in  an  aqueous  solution  of  that  substance  may  be 
ascertained  by  simple  evaporation ;  whilst  the  potassium  carbonate 
contained  in  a  solution  would  better  be  converted  into  potassium 
chloride,  by  evaporating  with  solution  of  ammonium  chloride. 

Precipitation  may  always  be  resorted  to,  whenever  the  substance 
in  solution  admits  of  being  converted  into  a  combination  which  i& 
insoluble  in  the  menstruum  present,  provided  that  the  precipitate 
is  fit  for  determination,  which  can  never  be  the  case  unless  it  can 
be  washed  and  is  of  constant  composition. 

§  41. 
a.  EVAPORATION. 

In  processes  of  evaporation  for  pharmaceutical  or  technico- 
chemical  purposes  the  principal  object  to  be  considered  is  saving 


§  41.]  EVAPOBATIOX.  67 

of  time  and  fuel ;  but  in  evaporating  processes  in  quantitative 
analytical  researches  this  is  merely  a  subordinate  point,  and  the 
analyst  has  to  direct  his  principal  care  and  attention  to  the  means 
of  guarding  against  loss  or  contamination  of  the  substance  operated 
upon. 

The  simplest  case  of  evaporation  is  when  we  have  to  concentrate 
a  clear  fluid,  without  carrying  the  process  to  dry  ness.  To  effect 
this  object,  the  fluid  is  poured  into  a  basin,  which  should  not  be 
filled  to  more  than  two-thirds.  Heat  is  then  applied  by  placing 
the  basin  either  on  a  water-bath,  sand-bath,  common  stove,  or 
heated  iron  plate,  or  over  the  flame  of  a  gas-  or  spirit-lamp,  care 
being  taken  always  to  guard  against  actual  ebullition,  as  this  in- 
variably and  unavoidably  leads  to  loss  from  small  drops  of  fluid 
spirting  out.  Evaporation  over  a  gas-  or  spirit-lamp,  when  con- 
ducted with  proper  care,  is  an  expeditious  and  cleanly  process. 
I>UXSEN'S  gas-lamp  may  be  used  most  advantageously  in  opera- 
tions of  this  kind ;  a  little  wire-gauze  cap,  loosely  fitted  upon 
the  tube  of  the  lamp,  is  a  material  improvement.  By  means  of 
tli is  simple  arrangement  it  is  easy  to  produce  even  the  smallest 
flame,  without  the  least  apprehension  of  ignition  of  the  gas  within 
the  tube. 

If  the  evaporation  is  to  be  effected  on  the  water-bath,  and  the 
operator  happens  to  possess  a  BEINDORF,  or  other  similarly-con- 
structed steam  apparatus,  the  evaporating- 
dish  may  be  placed  simply  into  an  opening 
corresponding  in  size.  Otherwise  recourse 
must  be  had  to  the  water-bath,  illustrated  by 

%  2T-. 

It  is  made  of  strong  sheet  copper,  and 
when  used  is  half  filled  with  water,  which  is  kept  boiling  over  a 
gas-,  spirit-,  or  oil-lamp.  The  breadth  from  a  to  b  should  be  from 
12  to  18  cm.  Various  flat  rings  of  the  same  outside  diameter  as 
the  top  of  the  bath,  and  adapted  to  receive  dishes  and  crucibles  of 
different  sizes,  are  essential  adjuncts  to  the  bath.  These  rings 
when  required  are  simply  laid  on  the  bath. 

It  will  occasionally  happen  that  the  water  in  the  bath  com- 
pletely evaporates ;  in  such  cases,  residues  are  heated  to  a  higher 
degree  than  is  desirable,  concentrated  solutions  spirt,  &c.  To 
avoid  these  inconveniences,  water-baths  have  been  devised  with 
an  arrangement  for  maintaining  a  constant  level  of  water. 


68  OPERATIONS.  [§41. 

If  the  operator  can  conduct  his  processes  of  evaporation  in  a 
room  set  apart  for  the  purpose,  where  he  may  easily  guard  against 
any  occurrence  tending  to  suspend  dust  in  the  air,  he  will  find  it 
no  very  difficult  task  to  keep  the  evaporating  fluid  clean  ;  in  this 
case  it  is  best  to  leave  the  dishes  uncovered.  But  in  a  large 
laboratory,  frequented  by  many  people,  or  in  a  room  exposed  to 
draughts  of  air,  or  in  which  coal  fires  are  burning,  the  greatest 
caution  is  required  to  protect  the  evaporating  fluid  from  contami- 
nation by  dust  or  ashes. 

For  this  purpose  the  evaporating  dish  is  either  covered'  with  a 
sheet  of  filtering-paper  turned  down  over  the  edges,  or  a  glass  rod 
twisted  into  a  triangular  shape  (fig.  28)  is  laid 
upon  it,  and  a  sheet  of  filtering-paper  spread 
over  it,  which  is  kept  in  position  by  a  glass  rod 
laid  across,  the  latter  again  being  kept  from 
rolling  down  by  the  slightly  turned  up  ends, 
a  and  Z»,  of  the  triangle. 

The  best  way,  however,  is  the  following : — Take  two  small 
thin  wooden  hoops  (fig.  29),  one  of  which  fits  loosely  in  the  other ; 
spread  a  sheet  of  blotting-paper  over  the  smaller 
one,  and  push  the  other  over  it.  This  forms  a 
cover  admirably  adapted  to  the  purpose  ;  and 
whilst  in  no  way  interfering  with  the  operation, 
it  completely  protects  the  evaporating  fluid 
from  dust,  and  may  be  readily  taken  off  ;  the  paper  cannot  dip 
into  the  fluid  ;  the  cover  lasts  a  long  time,  and  may,  moreover,  at 
any  time  be  easily  renewed. 

It  must  be  borne  in  mind,  however,  that  the  common  filtering- 
paper  contains  always  certain  substances  soluble  in  acids,  such  as 
lime,  ferric  oxide,  &c.,  which,  were  covers  of  the  kind  just 
described  used  over  evaporating  dishes  containing  a  fluid  evolving 
acid  vapors,  would  infallibly  dissolve  in  these  vapors,  and  the  solu- 
tion dripping  down  into  the  evaporating  fluid,  would  speedily  con- 
taminate it.  Care  must  be  taken,  therefore,  in  such  cases,  to  use 
only  such  filtering-paper  as  has  been  freed  by  washing  from  sub- 
stances soluble  in  acids. 

Evaporation  for  the  purpose  of  concentration  may  be  effected 
also  in  flasks;  these  are  only  half  filled,  and  placed  in  a  slanting 
position.  The  process  may  be  conducted  on  the  sand-bath,  or  over 
a  gas-  or  spirit-lamp,  or  even,  and  with  equal  propriety,  over  a  char- 


£  41.]  EVAPORATION.  69 

coal  fire.  In  cases  where  the.  operation  is  conducted  over  a  lamp 
or  a  charcoal  fire,  it  is  the  safest  way  to  place  the  flasks  on  wire 
ganze.  Gentle  ebullition  of  the  fluid  can  do  no  harm  here,  since 
the  slanting  position  of  the  flask  guards  effectively  against  risk  of 
loss  from  the  spirting  of  the  liquid.  Still  better  than  in  flasks,  the 
object  may  be  attained  by  evaporating  in  tubulated  retorts  with 
open  tubulure  and  neck  directed  obliquely  upwards.  The  latter 
acts  as  a  chimney,  and  the  constant  change  of  air  thus  effected  is 
extremely  favorable  to  evaporation. 

The  evaporation  of  fluids  containing  a  precipitate  is  best  con- 
ducted on  the  water-bath  ;  since  on  the  sand-bath,  or  over  the  lamp, 
it  is  next  to  impossible  to  guard  against  loss  from  bumping.  This 


Fig.  30. 

bumping  is  occasioned  by  slight  explosions  of  steam,  arising  from 
the  sediment  impeding  the  uniform  diffusion  of  the  heat.  Still 
there  remains  another,  though  less  safe  way,  viz.,  to  conduct  the 
evaporation  in  a  crucible  placed  in  a  slanting  position,  as  illus- 
trated in  fig.  30.  In  this  process,  the  flame  is  made  to  play  upon 
the  crucible  above  the  level  of  the  fluid. 

Where  a  fluid  has  to  be  evaporated  to  dryness,  as  is  so  often 
the  case,  the  operation  should  always,  if  possible,  be  terminated  on 
the  water-bath.  In  cases  where  the  nature  of  the  dissolved  sub- 
stance precludes  the  application  of  the  water-bath,  the  object  in 
view  may  often  be  most  readily  attained  by  heating  the  contents 


70  OPERATIONS.  [§  41. 

of  the  dish  from  the  top,  which  is  effected  by  placing  the  dish  in  a 
proper  position  in  a  drying  closet,  whose  upper  plate  is  heated  by 
a  flame  (that  of  the  water-  or  sand-bath)  passing  over  it.  If  the 
substance  is  in  a  covered  platinum  dish  or  crucible,  place  the  gas- 
lamp  in  such  a  position  that  the  flame  may  act  on  the  cover  from 
above. 

In  cases  where  the  heat  has  to  be  applied  from  the  bottom,  a 
method  must  be  chosen  which  admits  of  an  equal  diffusion  and 
ready  regulation  of  the  heat. 

An  air-bath  is  well  adapted  for  this  purpose,  i.e..  a  dish  of  iron 
plate,  in  which  the  porcelain  or  platinum  dish  is  to  be  placed  on  a 
wire  triangle,  so  that  the  two  vessels  may  be  at  all  points  i  to  |- 
inch  distant  from  each  other.  The  copper  apparatus,  flg.  27,  may7 
also  serve  as  an  air-bath,  although  I  must  not  omit  to  mention  that 
this  mode  of  application  will  in  the  end  seriously  injure  it.  If  the 
operation  has  to  be  conducted  over  a  lamp,  the  dish  should  be 
placed  high  above  the  flame  ;  best  on  wire  gauze,  since  this  will 
greatly  contribute  to  an  equal  diffusion  of  the,  heat.  The  use  of 
the  sand-bath  is  objectionable  here,  because  with  that  apparatus  we 
cannot  reduce  the  heat  so  speedily  as  may  be  desirable.  An  iron 
plate  heated  by  gas  may  perhaps  be  used  with  advantage.  But  no 
matter  which  method  be  employed,  this  rule  applies  equally  to  all  of 
them ;  that  the  operator  must  watch  the  process,  from  the  moment 
that  the  residue  begins  to  thicken,  in  order  to  prevent  spirting,  by 
reducing  the  heat,  and  breaking  the  pellicles  which  form  on  the 
surface,  with  a  glass  rod,  or  a  platinum  wire  or  spatula. 

Saline  solutions  that  have  a  tendency ',  upon  their  evaporation,  to 
creep  up  the  sides  of  the  vessel,  and  may  thus  finally  pass  over  the 
brim  of  the  latter,  thereby  involving  the  risk  of  a  loss  of  substance, 
should  be  heated  from  the  top,  in  the  way  just  indicated ;  since  by 
that  means  the  sides  of  the  vessel  will  get  heated  sufficiently  to 
cause  the  instantaneous  evaporation  of  the  ascending  liquid,  pre- 
venting thus  its  overflowing  the  brim.  The  inconvenience  just 
alluded  to  may,  however,  be  obviated  also,  in  most  cases,  by  cover- 
ing the  brim,  and  the  uppermost  part  of  the  inner  side  of  the  ves- 
sel, with  a  very  thin  coat  of  tallow,  thus  diminishing  the  adhesion 
between  the  fluid  and  the  vessel. 

In  the  case  of  liquids  evolving  gas-bubbles  upon  evaporating, 
particular  caution  is  required  to  guard  against  loss  from  spirting. 
The  safest  way  is  to  heat  such  liquids  in  an  obliquely-placed 


§  41.]  EVAPORATION.  71 

flask,  or  in  a  beaker  covered  with  a  large  watch-glass  ;  the  latter  is 
removed  as  soon  as  the  evolution  of  gas-bubbles  has  ceased,  and  the 
fluid  that  may  have  spirted  up  against  it  is  carefully  rinsed  into 
the  glass,  by  means  of  a  washing-bottle.  If  the  evaporation  has  to 
be  conducted  in  a  dish,  a  rather  capacious  one  should  be  selected, 
and  a  very  moderate  degree  of  heat  applied  at  first,  and  until  the 
evolution  of  gas  has  nearly  ceased. 

If  a  fluid  has  to  be  evaporated  vnth  exclusion  of  air,  the  best 
way  is  to  place  the  dish  under  the  bell  of  an  air-pump,  over  a  ves- 
sel with  sulphuric  acid,  and  to  exhaust;  or  a  tubulated  retort  may 
be  used  through  whose  tubulure  hydrogen  or  carbon  dioxide  is 
passed  by  the  acid  of  a  tube  not  quite  reaching  to  the  surface  of 
the  fluid. 

The  material  of  the  evaporating  vesxel*  may  exercise  a  much 
greater  influence  on  the  results  of  an  analysis  than  is  generally 
believed.  Many  rather  startling  phenomena  that  are  observed  in 
analytical  processes  may  arise  simply  from  a  contamination  of  the 
evaporated  liquid  by  the  material  of  the  vessel ;  great  errors  may 
also  spring  from  the  same  source. 

The  importance  of  this  point  has  induced  me  to  subject  it  to 
a  searching  investigation  (see  Appendix,  Analytical  Experiments, 
1 — 4),  of  which  I  will  here  briefly  intimate  the  results. 

Distilled  water  kept  boiling  for  some  length  of  time  in  glass 
I  flasks  of  Bohemian  glass)  dissolves  very  appreciable  traces  of  that 
material.  This  is  owing  to  the  formation  of  soluble  silicates ;  the 
particles  dissolved  consist  chiefly  of  potassa,  or  soda  and  lime,  in 
combination  with  silicic  acid.  A  much  larger  proportion  of  the 
glass  is  dissolved  by  water  containing  caustic  or  carbonated  alkali ; 
boiling  solution  of  ammonium  chloride  also  strongly  attacks  glass 
vessels.  Boiling  dilute  acids,  witli  the  exception,  of  course,  of 
hydrofluoric  and  hydrofluosilicilic  acids,  exercise  a  less  powerful 
solvent  action  on  glass  than  pure- water.  Porcelain  (Berlin  dishes) 
is  much  less  affected  by  water  than  glass ;  alkaline  liquids  also 
exercise  a  less  powerful  solvent  action  on  porcelain  than  on  glass ; 
the  quantity  dissolved  is,  however,  still  notable.  Solution  of 
ammonium  chloride  acts  on  porcelain  as  strongly  as  on  glass; 
dilute  acids,  though  exercising  no  very  powerful  solvent  action  on 
porcelain,  yet  attack  that  material  more  strongly  than  glass.  It 
results  from  these  data,  that  in  analyses  pretending  to  a  high 
degree  of  accuracy,  platinum  or  platinum-indium  or  silver  dishes 


72  OPERATIONS.  [§  4W2. 

should  always  be  preferred.  The  former  may  be  used  in  all  cases 
where  no  free  chlorine,  bromine,  or  iodine  is  present  in  the  fluid, 
or  can  be  formed  during  evaporation.  Fluids  containing  caustic 
alkalies  may  safely  be  evaporated  in  platinum,  but  not  to  the  point 
of  fusion  of  the  residue.  Silver  vessels  should  never  be  used  to 
evaporate  acid  fluids  nor  liquids  containing  alkaline  sulphides ; 
but  they  are  admirably  suited  for  solutions  of  alkali  hydroxides 
and  carbonates,  as  well  as  of  most  normal  salts. 


§  42. 

We  come  now  to  weighing  the  residues  remaining  upon  the 
evaporation  of  fluids.  We  allude  here  simply  to  such  as  are 
soluble  in  water ;  those  which  are  separated  by  filtration  will  be 
treated  of  afterwards.  Residues  are  generally  weighed  in  the 
same  vessel  in  which  the  evaporation  has  been  completed,  for 
which  purpose  platinum  dishes,  from  4  to  8  cm.  in  diameter,  pro- 
vided with  light  covers,  or  large  platinum  cruci- 
bles, are  best  adapted,  since  they  are  lighter  than 
porcelain  vessels  of  the  same  capacity. 

However,  in  most  cases,  the  amount  of  liquid 
to  be  evaporated  is  too  large  for  so  small  a  vessel, 
and  its  evaporation  in  portions  would  occupy  too 
much  time.     The  best  way,  in  cases  of  this  kind, 
is  to  concentrate  the  liquid  first  in  a  larger  vessel, 
and  to  terminate  the  operation  afterwards  in  the 
smaller  weighing  vessel.     In  transferring  the  fluid  from  the  large;- 
to  the  smaller  vessel,  the  lip  of  the  former  is  slightly  greased,  and 
the  liquid  made  to  run  down  a  glass  rod.     (See  fig.  31.) 

Finally  the  large  vessel  is  carefully  rinsed  with  a  washing- 
bottle,  until  a  drop  of  the  last  rinsing  leaves  no  longer  a  residue 
upon  evaporation  on  a  platinum  knife.  When  the  fluid  has  thus 
been  transferred  to  the  weighing-vessel,  the  evaporation  is  com- 
pleted on  the  water-bath  and  the  residuary  substance  finally  ignited, 
provided,  of  course,  it  will  admit  of  this  process.  For  this  pur- 
pose the  dish  is  covered  with  a  lid  of  thin  platinum  (or  a  thin  glass 
plate),  and  then  placed  high  over  the  flame  of  a  lamp,  and  heated 
very  gently  until  all  the  water  which  may  still  adhere  to  the  sub- 
stance is  expelled  ;  the  dish  is  now  exposed  to  a  stronger,  and  finally 
to  a  red  heat.  (Where  a  glass  plate  is  used,  this  must,  of  course,  be 


EVAPORATION.  73 

removed  before  igniting.)  In  this  case  it  is  also  well  to  make  the 
flame  play  obliquely  on  the  cover  from  above,  so  as  to  ran  as 
little  risk  as  possible  of  loss  by  spirting.  After  cooling  in  a  desic- 
cator, the  covered  dish  is  weighed  with  its  contents.  When  oper- 
ating upon  substances  which  decrepitate,  such  as  sodium  chloride, 
for  instance,  it  is  advisable  to  expose  them — after  their  removal 
from  the  water-bath,  and  previously  to  the  application  of  a  naked 
flame — to  a  temperature  somewhat  above  100°,  either  in  the  air- 
bath,  or  on  a  sand-bath,  or  on  a  common  stove. 

If  the  residue  does  not  admit  of  ignition,  as  is  the  case,  for 
instance,  with  organic  substances,  ammonium  salts,  <fcc.,  it  is  dried 
at  a  temperature  suited  to  its  nature.  In  many  cases,  the  tempera- 
ture of  the  water-bath  is  sufficiently  high  for  this  purpose,  for  the 
drying  of  ammonium  chloride,  for  instance;  in  others,  the  air  or 
oil-bath  must  be  resorted  to.  (See  §§  29  and  30.)  Under  any  cir- 
cumstances, the  desiccation  must  be  continued  until  the  substance 
ceases  to  suffer  the  slightest  .diminution  in  weight,  after  renewed 
exposure  to  heat  for  half  an  hour.  The  dish  should  invariably  be 
covered  during  the  process  of  weighing. 

If,  as  will  frequently  happen,  we  have  to  deal  with  a  fluid  con- 
taining a  small  quantity  of  a  potassium  or  sodium  salt,  the  weight 
<>f  which  we  want  to  ascertain,  in  presence  of  a  comparatively  large 
amount  of  an  ammonium  salt,  which  has  been  mixed  with  it  in  the 
course  of  the  analytical  process,  I  prefer  the  following  method : 
The  saline  mass  is  thoroughly  dried,  in  a  large  dish,  on  the  water- 
bath,  or,  towards  the  end  of  the  process,  at  a  temperature  some- 
what exceeding  100°.  The  dry  mass  is  then,  with  the  aid  of  a 
platinum  spatula,  transferred  to  a  small  glass  dish,  which  is  put 
aside  for  a  time  in  a  desiccator.  The  last  traces  of  the  salt  left 
adhering  to  the  sides  and  bottom  "of  the  large  dish  are  rinsed  off 
with  a  little  water  into  the  small  dish,  or  the  large  crucible,  in 
which  it  is  intended  to  weigh  the  salt ;  the  water  is  then  evaporated, 
and  the  dry  contents  of  the  glass  dish  are  added  to  the  residue : 
the  ammonium  salts  are  now  expelled  by  ignition,  and  the  residu- 
ary fixed  salts  finally  weighed.  Should  some  traces  of  the  saline 
mass  adhere  to  the  smaller  glass  dish,  they  ought  to  be  removed 
and  transferred  to  the  weighing  vessel,  with  the  aid  of  a  little 
pounded  ammonium  chloride,  or  some  other  ammonium  salt,  as  the 
moistening  again  with  water  would  involve  an  almost  certain  loss 
of  substance. 


74  OPERATIONS.  [§  43. 

§43 
J.  PRECIPITATION. 

Precipitation  is  resorted  to  in  quantitative  analysis  far  more 
frequently  than  evaporation,  since  it  serves  not  merely  to  convert 
substances  into  forms  adapted  for  weighing,  but  also,  and  more 
especially,  to  separate  them  from  one  another.  The  principal  in- 
tention in  precipitation,  for  the  purpose  of  quantitative  estimations, 
is  to  convert  the  substance  in  solution  into  a  form  in  which  it  is 
insoluble  in  the  menstruum  present.  The  result  will,  therefore, 
cceteris  parifms,  be  the  more  accurate,  the  more  the  precipitated 
body  deserves  the  epithet  insoluble,  and  in  cases  where  precipi- 
tates are  of  the  same  degree  of  solubility,  that  one  will  suffer  the 
least  loss  which  comes  in  contact  writh  the  smallest  amount  of 
solvent. 

Hence  it  follows,  first,  that  in  all  cases  where  other  circum- 
stances do  not  interfere,  it  is  preferable  to  precipitate  substances 
in  their  most  insoluble  form ;  thus,  for  instance,  barium  had  better 
be  precipitated  as  sulphate  than  as  carbonate  ;-  secondly,  that  when 
we  have  to  deal  with  precipitates  that  are  not  quite  insoluble  in 
the  menstruum  present,  we  must  endeavor  to  remove  that  men- 
struum, as  far  as  practicable,  by  evaporation  ;  thus  a  dilute  solution 
of  strontium  should  be  concentrated,  before  proceeding  to  precipi- 
tate the  strontium  with  sulphuric  acid ;  and,  thirdly,  that  when  we 
have  to  deal  with  precipitates  slightly  soluble  in  the  liquid  present, 
but  insoluble  in  another  menstruum,  into  which  the  former  may 
be  converted  by  the  addition  of  some  substance  or  other,  we  ought 
to  endeavor  to  bring  about  this  modification  of  the  menstruum. 
Thus,  for  instance,  alcohol  may  be  added  to  "water,  to  induce  com- 
plete precipitation  of  ammonium  platinic  chloride,  lead  chloride, 
calcium  sulphate,  &c.;  thus  again,  ammonium  magnesium  phosphate 
may  be  rendered  insoluble  in  an  aqueous  menstruum  by  adding 
ammonia  to  the  latter,  &c. 

Precipitation  is  generally  effected  in  beakers.  In  cases,  how- 
ever, where  we  have  to  precipitate  from  fluids  in  a  state  of  ebulli- 
tion, or  where  the  precipitate  requires  to  be  kept  boiling  for  some 
time  with  the  fluid,  flasks  or  dishes  are  substituted  for  beakers, 
with  due  regard  always  to  the  material  of  which  they  are  made 
(see  Evaporation,  §  41,  at  the  end). 


§  44.]  DECANTATIOX.  75 

The  separation  of  precipitates  from  the  fluid  in  which  they  are 
suspended,  is  effected  either  by  deccuitation  or  filtration,  or  by 
both  these  processes  jointly.  But,  before  proceeding  to  the  sepa- 
ration of  the  precipitate  by  any  of  these  methods,  the  operator 
must  know  whether  the  precipitant  has  been  added  in  sufficient 
quantity,  and  whether  the  precipitate  is  completely  formed.  To 
determine  the  latter  point,  an  accurate  knowledge  of  the  properties 
of  the  various  precipitates  must  be  attained,  which  we  shall  en- 
deavor to  supply  in  the  third  section.  To  decide  the  former  ques- 
tion. it  is  usually  sufficient  to  add  to  the  fluid  (after  the  precipitate 
has  settled)  cautiously  a  fresh  portion  of  the  precipitant,  and 
to  note  if  a  further  turbidity  ensues.  This  test,  however,  is  not 
infallible,  when  the  precipitate  has  not  the  property  of  forming 
immediately  ;  as,  for  instance,  is  the  case  with  ammonium  phos- 
pho-molybdate.  When  this  is  apprehended,  pour  out  (or  transfer 
with  a  pipette)  a  small  quantity  of  the  clear  supernatant  fluid  into 
another  vessel,  add  some  of  the  precipitant,  warm  if  necessary  ; 
and  after  some  time  look  and  see  whether  a  fresh  precipitate  has 
formed.  As  a  general  rule,  the  precipitated  liquid  should  be 
allowed  to  stand  at  rest  for  several  hours,  before  proceeding  to  the 
separation  of  the  precipitate.  This  rule  applies  more  particularly 
to  crvstalline,  pulverulent,  and  gelatinous  precipitates,  whilst  curdy 
and  flocculent  precipitates,  more  particularly  when  the  precipitation 
was  effected  at  a  boiling  temperature,  may  often  be  filtered  off  im- 
mediately. However,  we  must  observe  here,  that  all  general  rules, 
in  this  respect,  are  of  limited  application. 


a.  SEPARATION  OF  PRECIPITATES  BY  DECANTATIOX. 

When  a  precipitate  subsides  so  completely  and  speedily  in  a 
fluid  that  the  latter  may  be  decanted  off  perfectly  clear,  or  drawn 
off  with  a  syphon,  or  removed  by  means  of  a  pipette,  and  that 
the  washing  of  the  precipitate  does  not  require  a  very  long  time, 
decantation  is  often  resorted  to  for  its  separation  and  washing  ; 
this  is  the  case,  for  instance,  with  chloride  of  silver,  metallic  mer- 
cury, cv;c. 

Decantation  will  always  be  found  a  very  expeditious  and  accu- 
rate method  of  separation,  if  the'  process  be  conducted  with  due 
care  ;  it  is  necessary,  however,  in  most  cases,  to  promote  the  speedy 


76  OPERATIONS.  [§  45. 

and  complete  subsidence  of  the  precipitate ;  and  it  may  be  laid  down 
as  a  general  rule,  that  heating  the  precipitate  with  the  fluid  will 
produce  the  desired  effect.  Nevertheless,  there  are  instances  in 
which  the  simple  application  of  heat  will  not  suffice ;  in  some  cases, 
as  with  silver  chloride,  for  instance,  agitation  must  be  resorted  to ; 
in  other  cases,  some  reagent  or  other  is  to  be  added — hydrochloric 
acid,  for  instance,  in  the  precipitation  of  mercury,  &c.  We  shall 
have  occasion,  subsequently,  in  the  fourth  section,  to  discuss  this 
point  more  fully,  when  we  shall  also  mention  the  vessels  best 
adapted  for  the  application  of  this  process  to  the  various  precipitates. 
•  After  having  washed  the  precipitate  repeatedly  with  fresh 
quantities  of  the  proper  fluid,  until  there  is  no  trace  of  a  dissolved 
substance  to  be  detected  in  the  last  rinsings,  it  is  placed  in  a 
crucible  or  dish,  if  not  already  in  a  vessel  of  that  description ;  the 
fluid  still  adhering  to  it  is  poured  off  as  far  as  practicable,  and  the 
precipitate  is  then,  according  to  its  nature,  either  simply  dried,  or 
heated  to  redness. 

A  far  larger  amount  of  water  being  required  for  washing  pre- 
cipitates by  decantation  than  on  filters,  the  former  process  can  be 
expected  to  yield  accurate  results  only  where  the  precipitates  are 
absolutely  insoluble.  For  the  same  reason,  decantation  is  riot  ordi- 
narily resorted  to  in  cases  where  we  have  to  determine  other  con- 
stituents in  the  decanted  fluid. 

The  decanted  fluid  must  be  allowed  to  stand  at  rest  from 
twelve  to  twenty-four  hours,  to  make  quite  sure  that  it  contains 
no  particles  of  the  precipitate ;  if,  after  the  lapse  of  this  time,  no 
precipitate  is  visible,  the  fluid  may  be  thrown  away ;  but  if  a  pre- 
cipitate has  subsided,  this  had  better  be  estimated  by  itself,  and  the 
weight  added  to  the  main  amount ;  the  precipitate  may,  in  such 
cases,  be  separated  from  the  supernatant  fluid  by  decantation,  or 
by  filtration. 

§45. 
/3.  SEPARATION  OF  PRECIPITATES  BY  FILTRATION. 

This  operation  is  resorted  to  whenever  decantation  is  imprac- 
ticable, and,  consequently,  in  the  great  majority  of  cases  ;  provided 
always  the  precipitate  is  of  a  nature  to  admit  of  its  being  com- 
pletely freed,  by  mere  washing  on  the  filter,  from  all  foreign 
substances.  Where  this  is  not  the  case,  more  particularly,  there- 
fore, with  gelatinous  precipitates,  aluminium  hydroxide  for  in- 


§  45.]  FILTRATION.  7? 

stance,  a  combination  of  decantation  and  filtration  is  resorted  to 
(§  4«)- 

aa.  FILTERING  APPARATUS. 

Filtration,  as  a  process  of  quantitative  analysis,  is  almost 
exclusively  effected  by  means  of  paper. 

Plain  circular  filters  are  most  generally  employed ;  plaited  fil- 
ters are  only  occasionally  used.  Much  depends  upon  the  quality 
of  the  paper.  Good  filtering  paper  must  possess  the  three  follow- 
ing properties: — 1.  It  must  completely  retain  the  finest  precipi- 
tates ;  2.  It  must  filter  rapidly ;  and  3.  It  must  be  as  free  as 
possible  from  any  admixture  of  inorganic  bodies,  but  more  espe- 
cially from  such  as  are  soluble  in  acid  or  alkaline  fluids. 

It  is  a  matter  of  some  difficulty,  however,  to  procure  paper 
fullv  answering  these  conditions.  The  Swedish  filtering,  paper, 
with  the  water-mark  J.  H.  MUNKTELL,  is  considered  the  best,  and, 
consequently,  fetches  the  highest  price ;  but  even  this  answers  only 
the  first  two  conditions,  being  by  no  means  sufficiently  pure  for 
very  accurate  analyses,  since  it  leaves  upon  incineration  about  0*3 
per  cent,  of  ash,*  and  yields  to  acids  perceptible  traces  of  lime,  mag- 
nesia, and  ferric  oxide.  For  exact  experiments  it  is,  consequently, 
necessary  first  to  extract  the  paper  with  dilute  hydrochloric  acid, 
then  to  wash  the  acid  completely  out  with  water,  and  finally  to 
dry  the  paper.  In  the  case  of  very  fine  filtering  paper,  the  best 
way  to  perform  this  operation  is  to  place  the  ready-cut  filters, 
several  together,  in  a  funnel,  exactly  the  same  way  as  if  intended 
for  immediate  filtration ;  they  are  then  moistened  with  a  mixture 
of  one  part  of  ordinary  pure  hydrochloric  acid  with  two  parts  of 
water,  which  is  allowed  to  act  on  them  for  about  ten  minutes : 
after  this  all  traces  of  the  acid  are  carefully  removed  by  washing 
the  filters  in  the  funnel  repeatedly  with  warm  water.  The  funnel 
being  then  covered  with  a  piece  of  paper,  turned  over  the  edges, 
is  put  in  a  warm  place  until  the  filters  are  dry.  Compare  the 
instruction  given  in  the  "Qual.  Anal.,"  Am.  Ed.,  p.  8,  on  the 
preparation  of  washed  filters.  Filter  paper  containing  lead,  and 
which  is  consequently  blackened  by  sulphuretted  hydrogen,  should 
be  rejected. 

*  Plantamour  found  the  ash  of  Swedish  filtering  paper  to  consist  of  63 '23 
silicic  acid,  12'83  lime,  6 '21  magnesia,  2'94  alumina,  and  13'92  ferric  oxide,  in  100 
parts. 


78 


OPERATIONS. 


[§45. 


Heady-cut  filters  of  various  sizes  should  always  be  kept  on  hand. 
Filters  are  either  cut  by  circular  patterns  of  pasteboard  or  tin,  or, 

still  better,  by  MOHB'S  filter- 
patterns,  fig.  32.  This  little 
apparatus  is  made  of  tin-plate, 
and  consists  of  two  parts.  £  is 
a  quadrant  fitting  in  A,  whose 
straight  edges  are  turned  up, 


32  and  which  is  slightly  smaller 

than  B.  T.he  sheets  of  filter- 
paper  are  first  cut  up  into  squares,  which  are  folded  in  quarters, 
and  placed  in  A,  then  B  is  placed  on  the  top,  and  the  free  edge  of 
the  paper  is  cut  off  with  scissors.  Filters  cut  in  this  way  are  per- 
fectly circular,  and  of  equal  size. 

Several  pairs  of  these  patterns  of  various  sizes  (3,  4,  5,  6,  6*5, 
and  8  cm.  radius)  should  be  procured.  In  taking  a  filter  for  a 
given  operation,  you  should  always  choose  One  which,  after  the 
fluid  has  run  through,  will  not  be  more  than  half  filled  with  the 
precipitate. 

As  to  the  funnels,  they  should  be  inclined  at  the  angle  of  60% 
and  not  bulge  at  the  sides.  Glass  is  the  most  suitable  material  for 
them. 


Fig.  33. 


Fig.  34. 


The  filter  should  never  protrude  beyond  the  funnel.     It  should 
come  up  to  one  or  two  lines  from  the  edge  of  the  latter. 


£  46.]  FILTRATION.  79 

The  lilter  is  firmly  pressed  into  the  funnel,  to  make  the  paper 
fit  closely  to  the  side  of  the  latter;  it  is  then  moistened  with 
water ;  any  extra  water  is  not  poured  out,  but  allowed  to  drop 
through. 

The  stands  shown  in  figs.  33  and  34  complete  the  apparatus  for 
filtering. 

The  stands  are  made  of  hard  wood.  The  arm  holding  the 
funnel  or  funnels  must  slide  easily  up  and  down,  and  be  fixable  by 
the  screw.  The  holes  for  the  funnels  must  be  cut  conically,  to 
keep  the  funnels  steadily  in  their  place. 

These  stands  are  very  convenient,  and  may  be  readily  moved 
about  without  interfering  with  the  operation. 

§46. 

1>1>.    RULES    TO    BE    OBSERVED    IN    THE    PROCESS    OF    FlLTRATION. 

In  the  ease  of  curdy,  flocculent,  gelatinous,  or  crystalline  pre- 
cipitates there  is  no  danger  of  the  fluid  passing  turbid  through  the 
filter.  But  with  fine  pulverulent  precipitates  it  is  generally  n> 
.sv//-y,  and  always  advisable,  to  let  the  precipitate  subside,  and  then 
filter  the  supernatant  liquid,  before  proceeding  to  place  the  precipi- 
tate upon  the  filter.  We  generally  proceed  in  this  way  also  wit]) 
other  kinds  of  precipitates,  especially  with  those  that  require  to 
stand  long  before  they  completely  separate.  Precipitates  which 
have  been  thrown  down  hot,  are  most  properly  filtered  off  before 
cooling  (provided  always  there  be  no  objections  'to  this  course), 
since  hot  fluids  run  through  the  filter  more  speedily  than  cold  ones. 
S<  .me  precipitates  have  a  tendency  to  be  carried  through  the  filter 
along  with  the  fluid  ;  this  may  be  prevented  in  some  instances  by 
modifying  the  latter.  Thus  barium  sulphate,  when  filtered  from 
an  aqueous  solution,  passes  rather  easily  through  the  filter — the 
addition  of  hydrochloric  acid  or  ammonium  chloride  prevents  this 
in  a  great  measure. 

If  the  operator  finds,  during  a  filtration,  that  the  filter  would 
be  much  more  than  half  filled  by  the  precipitate,  he  would  better 
use  an  additional  filter,  and  thus  distribute  the  precipitate  over  the 
two  ;  for,  if  the  first  were  too  full,  the  precipitate  could  not  be 
properly  washed. 

The  fluid  ought  never  to  be  poured  directly  upon  the  filter, 
but  always  down  a  glass  rod,  and  the  lip  or  rim  of  the  vessel  from 


80  OPERATIONS.  [§  40. 

which  the  fluid  is  poured  should  always  be  slightly  greased  with 
tallow.*  The  stream  ought  invariably  to  be  directed  towards  the 
sides  \of  the  filter,  never  to  the  centre,  since  this  might  occasion 
loss  by  splashing.  In  cases  where  the  fluid  has  to  be  filtered  off, 
with  the  least  possible  disturbance  of  the  precipitate,  the  glass  rod 
must  not  be  placed,  during  the  intervals,  in  the  vessel  containing 
the  precipitate ;  but  it  may  conveniently  be  put  into  a  clean  glass, 
which  is  finally  rinsed  with  the  wash-water. 

The  filtrate  is  received  either  in  flasks,  beakers,  or  dishes, 
according  to  the  various  purposes  for  which  it  may  be  intended. 
Strict  care  should  be  taken  that  the  drops  of  fluid  filtering  through 
glide  down  the  side  of  the  receiving  vessel ;  they  should  never  be 
allowed  to  fall  into  the  centre  of  the  filtrate,  since  this  again 
might  occasion  loss  by  splashing.  The  best  method  is  that  shown 
in  fig.  34,  viz.,  to  rest  the  point  of  the  funnel  against  the  upper 
part  of  the  inside  of  the  receiving  vessel. 

If  the  process  of  filtration  is  conducted  in  a  place  perfectly 
free  from  dust,  there  is  no  necessity  to  cover  the  funnel,  nor  the 
vessel  receiving  the  filtrate  ;  however,  as  this  is  but  rarely  the  case, 
it  is  generally  indispensable  to  cover  both.  This  is  best  effected 
with  round  plates  of  sheet-glass.  The  plate  used  for  covering  the 
receiving  vessel  should  have  a  small  U-shaped  piece  cut  out  of  its 
edge,  large  enough  for  the  funnel-tube  to  go  through.  The  effect 
desired  may  be  produced  by  cautiously  chipping  out  the  glass  bit 
by  bit  with  the  aid  of  a  key.  Plates  perforated  in  the  centre  are 
worthless  as  regards  the  object  in  view. 

After  the  fluid  and  precipitate  have  been  transferred  to  the 
filter,  and  the  vessel  which  originally  contained  them  has  been, 
rinsed  repeatedly  with  water,  it  happens  generally  that  small  par- 
ticles of  the  precipitate  remain  adhering  to  the  vessel,  which  can- 
not be  removed  with  the  glass  rod.  From  beakers  or  dishes  these 
particles  may  be  readily  removed  by  means  of  a  feather  prepared 
for  the  purpose  by  tearing  off  nearly  the  whole  of  the  plumules, 
leaving  only  a  small  piece  at  the  end  which  should  be  cut  per- 
fectly straight.  From  flasks,  minute  portions  of  heavy  precipitates 
which  are  not  adherent,  are  readily  removed  by  blowing  a  jet  of 
water  into  the  flask,  held  inverted  over  the  funnel ;  this  is  effected 

*  The  tallow  may  be  kept  under  the  edge  of  the  work-table  at  a  convenient 
point,  where  it  will  adhere  by  a  little  pressure.  The  best  way  of  applying  the 
tallow  to  the  lip  of  a  vessel  is  with  the  greased  finger. 


47.] 


FILTEATIO^. 


81 


by  means  of  the  washing-bottle  shown  in  fig.  36.  If  the  minute 
adhering  particles  of  a  precipitate  cannot  be  removed  by  mechani- 
cal means,  solution  in  an  appropriate  menstruum  must  be  resorted 
to,  followed  by  re-precipitation.  Bodies  for  which  we  possess  no 
solvent,  such  as  barium  sulphate,  for  instance,  must  not  be  precipi- 
tated in  flasks, 

§47. 
cc.  WASHING  OF  PRECIPITATES. 

After  having  transferred  the  precipitate  completely  to  the  fil- 
ter, we  have  next  to  perform  the  operation  of  washing ;  this  is 
effected  by  means  of  one  of  the  well-known  washing-bottles,  of 
which  I  prefer  the  one  represented  in  fig.  35  in  every  respect. 
The  doubly  perforated  stoppers  are  of  vulcanized  rubber. 


Fig.  35. 


Fig.  36. 


Fig.  37. 


Care  must  always  be  taken  to  properly  regulate  the  jet,  as  too 
impetuous  a  stream  of  water  might  occasion  loss  of  substance. 

In  cases  where  a  precipitate  has  to  be  washed  with  great  cau- 
tion, the  apparatus  illustrated  in  fig.  37  will  be  found  to  answer 
very  well. 

The  construction  of  this  apparatus  requires  no  explanation. 
When  the  flask  is  inverted,  it  supplies  a  fine  continuous  jet  of  water. 

Precipitates  requiring  washing  with  water,  are  washed  most 
expeditiously  with  hot  water,  provided  always  there  be  no  special 
reason  against  its  use.  The  washing-bottle  shown  in  fig.  35  is 
particularly  well  adapted  for  this  purpose.  The  cork  which  is 
fastened  to  the  neck  of  the  flask  with  wire  serves  to  facilitate 
holding  it. 


82  OPERATIONS.  [§  48. 

It  is  a  rule  in  washing  precipitates  not  to  add  fresh  wash-water 
to  the  filter  till  the  old  has  quite  run  through.  In  applying  the 
jet  of  water  you  have  to  take  care  on  the  one  hand  that  the  upper 
edge  of  the  filter  is  properly  washed,  and  on  the  other  hand  that 
no  canals  are  formed  in  the  precipitate,  through  which  the  fluid 
runs  off,  without  coming  in  contact  with  the  whole  of  the  precipi- 
tate. If  such  canals  have  formed  and  cannot  be  broken  up  by 
the  jet,  the  precipitate  must  be  stirred  cautiously  with  a  small 
platinum  knife  or  glass  rod. 

The  washing  may  be  considered  completed  wrhen  all  soluble 
matter  that  is  to  be  removed  has  been  got  rid  of.  The  beginner 
who  devotes  proper  attention  to  the  completion  of  this  operation 
shuns  one  of  the  rocks  which  he  is  most  likely  to  encounter. 
Whether  the  precipitate  has  been  completely  washed  may  generally 
be  ascertained  by  slowly  evaporating  a  drop  of  the  last  washings 
upon  a  platinum  knife,  and  observing  if  a  residue  is  left.  But  in 
cases  where  the  precipitate  is  not  altogether  insoluble  in  water 
(strontium  sulphate,  for  instance),  recourse  must  be  had  to  more 
special  tests,  which  we  shall  have  occasion  to  point  out  in  the 
course  of  the  work.  The  student  should  never  discontinue  the 
washing  of  a  precipitate  because  he  simply  imagines  it  is  finished 
—he  must  be  certain. 

§48. 
y.  SEPARATION  OF  PRECIPITATES  BY  DECANT  ATION  AND  FILTRATION 

COMBINED. 

In  the  case  of  precipitates  which,  from  their  gelatinous  nature, 
or  from  the  firm  adhesion  of  certain  coprecipitated  salts,  oppose 
insuperable,  or,  at  all  events,  considerable  obstacles  to  perfect  wash- 
ing on  the  filter,  the  following  method  is  resorted  to :  Let  the 
precipitate  subside  as  far  as  practicable,  pour  the  nearly  clear  super- 
natant liquid  on  the  filter,  stir  the  precipitate  up  wTith  the  washing 
fluid  (in  certain  cases,  where  such  a  course  is  indicated,  heat  to 
boiling),  let  it  subside  again,  and  repeat  this  operation  until  the 
precipitate  is  almost  thoroughly  washed.  Transfer  it  now  to  the 
filter,  and  complete  the  operation  with,  the  washing-bottle  (see 
§  47).  This  method  is  highly  to  be  recommended;  there  are 
many  precipitates  that  can  be  thoroughly  \vashed  only  by  its 
application. 


§  49.]  FILTRATION".  83 

In  cases  where  it  is  not  intended  to  weigh  the  precipitate 
washed  by  decantation,  but  to  dissolve  it  again,  the  operation  of 
washing  is  entirely  completed  by  decantation,  and  the  precipitate 
not  even  transferred  to  the  filter.  The  re-solution  of  the  bulk  of 
the  precipitate  being  effected  in  the  vessel  containing  it,  the  filter 
is  placed  over  the  latter,  and  the  solvent  passed  through  it. 
Although  the  termination  of  the  operation  of  washing  may  be 
usually  ascertained  by  testing  a  sample  of  the  washings  for  one  of 
the  substances  originally  present  in  the  solution  which  has  to  be 
removed  (for  hydrochloric  acid,  for  instance,  with  nitrate  of 
silver),  still  there  are  cases  in  which  this  mode  of  proceeding  is 
inapplicable.  In  such  cases,  and  indeed  in  processes  of  washing  by 
decantation  generally,  BUNSEN'S  method  will  be  found  convenient 
— viz.,  to  continue  the  process  of  washing  until  the  fluid  which 
had  remained  in  the  beaker,  after  the  first  decantation,  has  under- 
gone a  ten  thousand- fold  dilution.  To  effect  this,  measure  with  a 
slip  of  paper  the  height  from  the  bottom  of  this  beaker  to  the 
surface  of  the  fluid  remaining  in  it,  together  with  the  precipitate, 
after  the  first  decantation;  then  fill  the  beaker  with  water,  if 
possible,  boiling,  and  measure  the  entire  height  of  the  fluid; 
divide  the  length  of  the  second  column  by  that  of  the  first.  Go 
through  the  same  process  each  time  you  add  fresh  water,  and 
always  multiply  the  quotient  found  witli  the  number  obtained  in 
the  preceding  calculation,  until  you  reach  10000. 

§49. 
FURTHER  TREATMENT  OF  PRECIPITATES. 

Before  proceeding  to  weigh  a  precipitate,  it  still  remains  to 
convert  it  into  a  form  of  accurately  known  composition.  This  is 
done  either  by  igniting  or  by  drying.  The  latter  proceeding  is 
more  protracted  and  tedious  than  the  former,  and  is,  moreover,  apt 
to  give  less  accurate  results.  The  process  of  drying  is,  therefore, 
;is  a  general  rule,  applied  only  to  precipitates  which  cannot  bear 
exposure  to  a  red  heat  without  undergoing  total  or  partial  volatili- 
zation ;  or  whose  residues  left  upon  ignition  have  no  constant  com- 
position ;  thus,  for  instance,  drying  is  resorted  to  in  the  case  of 
mercuric  sulphide,  arsenious  sulphide,  and  other  metallic  sulphides ; 
and  also  in  the  case  of  silver  cyanide,  potassium  platinic  chloride, 
etc. 


84  OPERATIONS.  [§  50. 

But  whenever  the  nature  of  the  precipitate  (<?.</.,  barium  sul- 
phate, lead  sulphate,  and  many  other  compounds)  leaves  the  opera- 
tor at  liberty  to  choose  between  drying  and  heating  to  redness,  the 
process  is  almost  invariably  preferred. 


aa.  Drying  of  Precipitates. 

When  a  precipitate  has  been  collected,  washed,  and  dried  on  a 
filter,  minute  particles  of  it  adhere  so  firmly  to  the  paper  that  it  is 
found  impossible  to  remove  them.  The  weighing  of  dried  precipi- 
tates involves,  therefore,  in  all  accurate  analyses,  the  drying  and 
weighing  of  the  filter  also.  To  obtain  accurate  results,  it  is  neces- 
sary to  dry  and  weigh  the  filter  before  using  it ;  the  temperature  at 
which  the  filter  is  dried  must  be  the  same  as  that  to  which  it  is 
intended  subsequently  to  expose  the  precipitate.  Another  condi- 
tion is  that  the  filtering-paper  must  not  contain  any  substance 
liable  to  be  dissolved  by  the  fluid  passing  through  it. 

The  drving  is  conducted  either  in  the  water-,  air-,  or  oil-bath, 
according  to  the  degree  of  heat  required.  The  weighing  is  per- 
formed in  a  closed  vessel,  mostly  between  two  clasped  watch-glasses 
(fig.  20),  or  in  a  platinum  crucible.  When  the  filter  appears  dry, 
it  is  placed  between  the  warm  watch-glasses,  or  in  a  warm  crucible, 
allowed  to  cool  under  a  bell-glass,  over  sulphuric  acid,  and  weighed. 
The  reopened  crucible  or  watch-glasses,  together  with  the  filter,  are 
then  again  exposed  for  some  time  to  the  required  degree  of  heat, 
and,  after  cooling,  weighed  once  more.  If  the  weight  does  not 
differ  from  that  found  at  first,  the  filter  may  be  considered  dry, 
and  we  have  simply  to  note  the  collective  weight  of  the  watch- 
glasses,  clasp,  and  filter,  or  of  the  crucible  and  filter. 

After  the  washing  of  the  precipitate  has  been  concluded  and 
the  water  allowed  to  run  off  as  far  as  possible,  the  filter  with  the 
precipitate  is  taken  off  the  funnel,  folded  up,  and  placed  upon 
blotting-paper,  which  is  then  kept  for  some  time  in  a  moderately 
warm  place  protected  from  dust ;  it  is  finally  put  into  one  of 
the  watch-glasses,  or  into  the  uncovered  platinum  crucible,  with 
which  it  was  first  weighed,  and  exposed  to  the  appropriate  degree 
of  heat,  either  in  the  water-,  air-,  or  oil-bath.  When  it  is  judged 
that  the  precipitate  is  dry,  the  second  watch-glass,  or  the  lid  of  the 
crucible  is  put  on  (with  the  clasp  pushed  over  the  two  in  the  former 


Jj  51.]  DRYING   OF   PRECIPITATES.  85 

case),  and  the  whole,  after  cooling  in  the  desiccator,  is  weighed. 
The  filter  and  the  precipitate  are  then  again  exposed,  in  the  same 
way,  to  the  proper  drying  temperature,  allowed  to  cool,  and 
weighed  again,  the  same  process  being  repeated  until  the  weight 
remains  constant  or  varies  only  to  the  extent  of  a  few  deci-milli- 
grammes.  By  subtracting  from  the  weight 
found  the  tare  of  the  crucible  or  watch-glasses 
and  filter,  we  obtain  the  weight  of  the  dry 
precipitate.  [The  filter  must  not  be  dried  too 
long,  as  it  slowly  loses  weight,  and  even  be- 
comes brown  from  decomposition  when  heated 
to  100°  for  days  together.] 

It  happens  sometimes  that  the  precipitate 
nearly  fills  the  filter,  or  retains  a  considerable 

amount  of  water;  or  sometimes  the  paper  is  so  thin  that  its  re- 
moval from  the  funnel  cannot  well  be  effected  without  tearing. 
In  all  such  cases,  the  best  way  is  to  let  the 
filter  and  precipitate  get  nearly  dry  in  the 
funnel,  which  may  be  effected  readily  by 
covering  the  latter  with  a  piece  of  blotting 
paper*  to  keep  out  the  dust,  and  placing 
it,  supported  on  a  broken  beaker  (fig.  38), 
or  some  other  vessel  of  the  kind,  on  the 
steam-apparatus  or  sand-bath,  or  stove,  or 
39'  on  a  heated  iron  plate.  For  support  to  a 

funnel  while  drying  a  hollow  frustum  of  a  cone  open  both  ends, 
made  of  sheet  zinc  (fig.  39),  is  convenient.  Two  sizes  may  be  used, 
10  cm.  and  12  cm.  high  respectively.  The  lower  diameter  should 
be  from  7  to  8,  the  upper  from  ±  to  6  cm. 

£  •>!. 
U>.  Ignition  of  Precipitates. 

In  this  process  it  is  necessarv  to  burn  the  filter  and  substract 
the  weight  of  the  filter  ash  from  the  total  weight  found. 

If  care  be  taken  to  make  the  filters  always  of  the  same  paper, 

*  Turned  down  over  the  rim.  Or  more  neatly  as  follows: — Wet  a  common 
cut  filter,  stretch  it  over  the  ground  top  of  the  funnel,  and  then  gently  tear  off 
the  superfluous  paper.  The  cover  thus  formed  continues  to  adhere  after  drying 
with  some  force. 


86  OPEKATIONS.  [§  51. 

and  to  cut  every  size  by  a  pattern,  the  quantity  of  ash  which  each 
size  yields  upon  incineration  may  be  readily  determined.  It  is 
necessary,  however,  to  determine  separately  the  quantity  of  ash 
left  by  ordinary  filters,  and  that  left  by  filters  which  have  been 
washed  with  hydrochloric  acid  and  water ;  on  an  average  the  latter 
leave  about  half  as  much  ash  as  the  former.  To  determine  the  fil- 
ter ash  take  ten  filters  (or  an  equal  weight  of  cuttings  from  the 
same  paper),  burn  them  in  an  obliquely-placed  platinum  crucible, 
and  ignite  until  every  trace  of  carbon  is  consumed ;  then  weigh 
the  ash,  and  divide  the  amount  found  by  ten;  the  quotient  ex- 
presses, with  sufficient  precision,  the  average  quantity  of  ash  which 
every  individual  filter  leaves  upon  incineration. 

In  the  ignition  of  precipitates,  the  following  four  points  have 
to  be  more  particularly  regarded: 

1.  No  loss  of  substance  must  be  incurred ; 

2.  The  ignited  precipitates  must  really  be  the  bodies  they  are 
represented  to  be  in  the  calculation  of  the  results ; 

3.  The  incineration  of  the  filters  must  be  complete ; 

4.  The  crucibles  must  not  be  attacked. 

The  following  two  methods  seem  to  me  the  simplest  and  most 
appropriate  of  all  that  have  as  yet  been  proposed.  The  selection 
of  either  depends  upon  certain  circumstances,  which  I  shall  imme- 
diately have  occasion  to  point  out.  But  no  matter  which  method 
is  resorted  to,  the  precipitate  must  always  be  thoroughly  dried, 
before  it  can  properly  be  exposed  to  a  red  heat.  The  application 
of  a  red  heat  to  moist  precipitates,  more  particularly  to  such  as  are 
very  light  and  loose  in  the  dry  state  (silicic  acid,  for  instance), 
involves  always  a  risk  of  loss  from  the  impetuously  escaping 
aqueous  vapors  carrying  away  with  them  minute  particles  of  the 
substance.  Some  other  substances,  as  aluminium  hydroxide  or 
ferric  hydroxide,  for  instance,  form  small  hard  lumps ;  if  such 
lumps  are  ignited  while  still  moist  within  they  are  liable  to  fly 
about  with  great  violence.  The  best  method  of  drying  precipitates 
as  a  preliminary  to  ignition  is  as  described  in  §  50,  the  last 
paragraph. 

Respecting  the  ignition,  the  degree  of  heat  to  be  applied  and 
the  duration  of  the  process  must,  of  course,  depend  upon  the 
nature  of  the  precipitate  and  upon  its  deportment  at  a  red  heat. 
As  a  general  rule,  a  moderate  red  heat,  applied  for  about  five 
minutes,  is  found  sufficient  to  effect  the  purpose ;  there  are,  how- 


§  51.]  IGNITIC^    OF    PRECIPITATES.  87 

ever,  many  exceptions  to  this  rule  which  will  be  indicated  where- 
ever  they  occur. 

Whenever  the  choice  is  permitted  between  porcelain  and 
platinum  crucibles,  the  latter  are  always  preferred,  on  account  of 
their  comparative  lightness  and  infrangibility,  and  because  they 
are  more  readily  heated  to  redness.  The  crucible  .selected  should 
always  be  of  sufficient  capacity,  as  the  use  of  crucibles  deficient  in 
size  involves  the  risk  of  loss  of  substance.  The  proper  size,  in 
most  cases,  is  4  cm.  in  height,  and  3*5  cm.  in  diameter.  That  the 
crucible  must  be  perfectly  clean,  both  inside  and  outside,  need 
hardly  be  mentioned.  The  analyst  should  acquire  the  habit  of 
cleaning  and  polishing  the  platinum  crucible  always  after  using  it. 
This  should  be  done  by  friction  with  moist  sea-sand  whose  grains 
are  all  round  and  do  not  scratch.  The  sand  is  rubbed  on  with  the 
finger,  and  the  desired  effect  is  produced  in  a  few  minutes.  The 
adoption  of  this  habit  is  attended  with  the  pleasure  of  always 
working  with  a  bright  crucible  and  the  profit  of  prolonging  its 
existence.  This  mode  of  cleaning  is  all  the  more  necessary,  when 
one  ignites  over  gas-lamps,  since  at  this  high  temperature  crucibles 
soon  acquire  a  gray  coating,  which  arises  from  a  superficial  loosen- 
ing of  the  platinum.  A  little  burnishing  with  sea-sand  readily 
removes  the  appearance  in  question,  without  causing  any  notable 
diminution  of  the  weight  of  the  crucible.  The  foregoing  remarks 
on  platinum  crucibles  refer  equally  to  those  of  iridium-platinum — 
which,  by  the  by,  are  now  much  used,  and  very  highly  to  be  recom- 
mended— only  the  restoration  of  the  polish  is  somewhat  more  diffi- 
cult with  the  latter,  on  account  of  the  greater  hardness  of  the  alloy. 
If  there  are  spots  on  the  platinum  or  iridium-platinum  crucibles, 
which  cannot  be  removed  by  the  sand  without  wearing  away  too 
much  of  the  metal,  a  little  potassium  disulphate  is  fused  in  the 
crucible,  the  fluid  mass  shaken  about  inside,  allowed  to  cool,  and 
the  crucible  finally  boiled  with  water.  There  are  two  ways  of 
cleaning  crucibles  soiled  outside  ;  either  the  crucible  is  placed  in  a 
larger  one,  and  the  interspace  filled  with  potassium  disulphate, 
which  is  then  heated  to  fusion ;  or  the  crucible  is  placed  on  a 
platinum-wire  triangle,  heated  to  redness,  and  then  sprinkled  over 
with  powdered  potassium  disulphate.  Instead  of  the  sulphate  you 
may  use  borax,  ^ever  forget  at  last  to  polish  the  crucible  with 
sea-sand  again. 

When  the  crucible  is  clean,  it  is  placed  upon  a  clean  platinum- 


88  OPERATIONS.  [§  52, 

wire  triangle  (fig.  40),  ignited,  allowed  to  cool  in  the  desiccator, 
and  weighed.  This  operation,  though  not  indispensable,  is  still 
always  advisable,  that  the  weighing  of  the  empty  and  filled  crucible 
may  be  performed  under  as  nearly  as  possible  the  same  circum- 
stances. The  empty  crucible  may  of  course  be  weighed  after  the 
ignition  of  the  precipitate  ;  however,  it  is 
preferable  in  most  cases  to  weigh  it  before. 
The  ignition  is  effected  with  a  BERZELIUS 
spirit-lamp  or  a  gas-lamp,  or  else  in  a  muffle. 
In  igniting  reducible  substances  over  lamps, 
the  analyst  must  always  be  on  his  guard 
against  the  contact  of  unconsumed  hydro- 
carbons  even  in  covered  crucibles.  When 
gas-lamps  are  used  there  is  especial  need  of 
caution  in  this  respect.  Reduction  will  be  avoided  if  the  flame  is 
made  no  larger  than  necessary,  if  the  crucible  is  supported  in  the 
upper  part  of  the  flame,  and  if,  when  the  crucible  is  in  a  slanting 
position,  it  is  heated  from  behind. 

We  pass  on  now  to  the  description  of  the  special  methods. 


FIRST  METHOD.     (Ignition  of  the  Precipitate  with  the  Filter.) 

This  method  is  resorted  to  in  cases  where  there  is  no  danger  of 
a  reduction  of  the  precipitate  by  the  action  of  the  carbon  of  the 
filter.  The  mode  of  proceeding  is  as  follows  :  — 

The  perfectly  dry  filter,  with  the  precipitate,  is  removed  from 
the  funnel,  and  its  sides  are  gathered  together  at  the  top,  so  that 
the  precipitate  lies  enclosed  as  in  a  small  bag.  The  filter  is  now 
put  into  the  crucible,  which  is  then  covered  and  heated  over  a 
spirit-lamp  with  double  draught,  or  over  gas  very  gently,  to  effect 
the  slow  charring  of  the  filter;  the  cover  is  now  removed,  the 
crucible  placed  obliquely,  and  a  stronger  degree  of  heat  applied, 
until  complete  incineration  of  the  filter  is  effected  ;  the  lid,  which 
had  in  the  meantime  best  be  kept  on  a  porcelain  plate,  or  in  a  por- 
celain crucible,  is  put  on  again,  and  a  red  heat  applied  for  some 
time  longer,  if  needed  ;  the  crucible  is  now  allowed  to  cool  a  little, 
and  is  then,  while  still  hot,  though  no  longer  red  hot,*  taken  off 

*  Taking  hold  of  a  red  Jwt  crucible  with  brass  tongs  might  cause  the  formation 
of  black  rings  round  it. 


52.] 


IGXITIOX    OF    PRECIPITATES. 


89 


with  a  pair  of  tongs  of  brass  or  polished  iron  (fig.  -tl),  and  put  in 
the  desiccator,  where  it  is  left  to  cool ;  it  is  finally  weighed. 

The  combustion  of  the  carbon  of  the  filter  may  be  promoted, 
in  cases  where  it  proceeds  too  slowly,  by  pushing  the  non-consumed 
particles,  with  a  smooth  and  rather  stout  platinum  wire,  within  the 
focus  of  the  strongest  action  of  the  heat  and  air.  And  the  oper- 
ator may  also  increase  the  draught  of  ail*  by  leaning  the  lid  of  the 
crucible  against  the  latter  in  the  manner  illustrated  in  fig.  42. 

It  will  occasionally  happen  that  particles  of  the  carbon  of  the 
filter  obstinately  resist  incineration.  In  such  cases  the  operation 
may  be  promoted  by  putting  a  small  lump  of  fused,  dry  ammonium 


Fig.  41. 


Fig.  42. 


nitrate  into  the  crucible,  placing  on  the  lid  and  applying  a  gentle 
heat  at  first,  which  is  gradually  increased.  However,  as  this  way 
of  proceeding  is  apt  to  involve  some  loss  of  substance,  its  applica- 
tion should  not  be  made  a  general  rule. 

In  cases  where  the  bulk  of  the  precipitate  is  easily  detached 
from  the  filter,  the  preceding  method  is  occasionally  modified  in 
this,  that  the  precipitate  is  put  into  the  crucible,  and  the  filter, 
with  the  still  adhering  particles,  folded  loosely  together,  and  laid 
over  the  precipitate.  In  other  respects,  the  operation  is  conducted 
in  the  manner  above  described. 


90  OPERATIONS. 


SECOND  METHOD.     (Ignition  of  the  Precipitate  apart  from  the 

Filter.) 

This  method  is  resorted  to  in  cases  where  a  reduction  of  the 
precipitate  from  the  action  of  the  carbon  of  the  filter  is  appre- 
hended; and  also  where  the  ignited  precipitate  is  required  for 
further  examination,  which  the  presence  of  the  filter  ash  might 
embarrass.  It  may  be  employed  also,  instead  of  the  first  method, 
in  all  cases  where  the  precipitate  is  easily  detached  from  the  filter. 
The  mode  of  proceeding  is  as  follows : — 

The  crucible  intended  to  receive  the  precipitate  is  placed  upon 
a  sheet  of  glazed  paper ;  the  perfectly  dry  filter  with  the  precipi- 
tate is  taken  out  of  the  funnel,  and  gently  pressed  together  over 
the  paper,  to  detach  the  precipitate  from  the  filter ;  the  precipitate 
is  now  shaken  into  the  crucible,  and  the  particles  still  adhering  to 
the  filter  are  removed  from  it,  as  far  as  practicable,  by  further 
pressing  or  gentle  rubbing  together  of  the  folded  filter,  and  are 
then  also  transferred  to  the  crucible.  The  filter  is  now  spread 
open  upon  the  sheet  of  glazed  paper,  and  then  folded  in  form  of  a 
little  square  box,  enclosed  on  all  sides  by  the  parts  turned  up ;  any 
minute  particles  of  the  precipitate  that  may  have  dropped  on  the 
glazed  paper  are  brushed  into  this  little  box,  with  the  aid  of  a 
small  feather ;  the  box  is  closed  again,  rolled  up,  and  one  end  of  a 
long  platinum  wire  spirally  wound  round  it.  The  crucible  being 
placed  on  or  above  a  porcelain  plate,  the  little  roll  is  lighted,  and, 
during  its  combustion,  held  over  the  crucible,  so  that  the  falling 
particles  of  the  precipitate  or  filter  ash  may  drop  into  it,  or,  at 
least,  into  the  porcelain  plate.  In  this  way,  and  by  occasionally 
holding  the  little  roll  again  in  or  against  the  flame,  the  incineration 
of  the  filter  is  readily  and  safely  eifected.  "When  the  operation  is 
terminated,  a  slight  tap  will  suffice  to  drop  the  ash  and  the  remain- 
ing particles  of  the  precipitate  into  the  crucible,  which  is  then  cov- 
ered, and  the  ignition  completed  as  in  §  52.  "Where  it  is  intended 
to  keep  the  ash  separate  from  the  precipitate,  it  is  made  to  drop 
into  the  lid  of  the  crucible,  in  which  case  it  is  better  to  ignite  the 
crucible  with  the  principal  portion  of  the  precipitate  first.  This 
method  of  incinerating  the  filter,  devised  by  BTJNSEN,  is  preferable 
to  the  method  formerly  in  use,  in  which  the  filter,  freed,  as  far  as 


§  53,  a.]    BUNSEN'S  METHOD  OF  RAPID  FILTKATION.  91 

practicable,  from  the  precipitate,  was  burnt  either  whole  or  cut  up 
into  little  bits  on  the  lid  of  the  crucible,  the  operation  being  pro- 
moted when  necessary  by  gently  pressing  the  still  unconsumed 
particles  with  a  platinum  wire,  or  platinum  spatula,  against  the 
red-hot  lid.  Xo  matter  which  method  of  incineration  is  resorted 
to.  the  operation  must  always  be  conducted  in  a  spot  entirely  pro- 
tected from  draughts. 

Certain  precipitates  suffer  some  essential  modification  in  their 
properties,  in  their  solubility,  for  instance,  from  ignition.  In  cases 
where  a  portion  of  a  substance  of  the  kind  is  required,  after  the 
weighing,  for  some  other  purpose  with  which  the  effects  of  a  red 
heat  would  interfere,  the  two  operations  of  drying  and  igniting 
may  be  combined  in  the  following  way  :  —  The  precipitate  is  col- 
lected on  a  filter  dried  at  100°  ;  it  is  then  also  dried,  at  100°,  and 
weighed  ('£  50).  A  portion  of  the  dry  precipitate  is  put  into  a 
tared  crucible,  and  its  exact  weight  ascertained  ;  it  is  then  exposed 
to  a  red  heat,  allowed  to  cool  in  the  usual  way,  and  weighed  again  ; 
the  diminution  of  weight  which  it  has  undergone  is  calculated  on 
the  whole  amount  of  the  precipitate. 


SKX'S  MKTHOD  OF  RAPID  FILTRATION.* 


.V  precipitate  is  washed  either  by  filtration  or  by  decantation  : 
in  the  former  case  the  portion  of  liquid  not  mechanically  retained 
is  allowed  to  drain  from  the  precipitate  ;  in  the  latter  it  is  sepa- 
rated by  simply  pouring  it  away,  the  foreign  substances  contained 
in  the  precipitate  being  then  removed  by  the  repeated  addition  of 
some  washing-fluid,  in  each  successive  portion  of  which  the  pre- 
cipitate is,  as  far  as  possible,  uniformly  suspended,  this  process 
being  continued  until  the  amount  of  impurity  becomes  so  minute 
that  its  presence  may  be  entirely  disregarded. 

In  the  process  of  filtration  as  hitherto  conducted,  the  time  re- 
quired is  so  long  and  the  quantity  of  wash-water  needed  so  great 
that  some  simplification  of  this  continually  recurring  operation  is 
in  the  highest  degree  desirable.  The  following  method,  which  de- 
pends not  upon  the  removal  of  the  impurity  by  simple  attenuation, 
but  upon  its  displacement  by  forcing  the  wash-  water  through  the 

*  Ann.  derChem.  imdPharm.,  vol.  cxlviii.  p.  269;  Am.  Jour.  Sci.,  xlvii.  p.  321. 


92  OPERATIONS.  [§  53,  a. 

precipitate,  appears  to  me  to  combine  all  the  requisite  conditions 
and  therefore  to  satisfy  the  need. 

«/ 

The  rapidity  with  which  a  liquid  filters  depends,  cceteris 
paribus,  upon  the  difference  which  exists  between  the  pressure 
upon  its  upper  and  lower  surfaces.  Supposing  the  filter  to  consist 
of  a  solid  substance,  the  pores  of  which  suffer  no  alteration  by  pres- 
sure, or  by  any  other  influence,  then  the  volume  of  liquid  filtered 
in  the  unit  of  time  is  nearly  proportional  to  the  difference  in  pres- 
sure :  this  is  clearly  shown  by  the  following  experiments,  made 
with  pure  water  and  a  filter  consisting  of  a  thin  plate  of  artificial 
pumice-stone.  The  thin  plate  of  pumice  was  hermetically  fastened 
into  a  funnel  consisting  of  a  graduated  cylindrical  glass  vessel,  the 
lower  end  of  which  was  connected  with  a  large  thick  flask  by 
means  of  a  tightly  fitting  caoutchouc  cork.  The  pressure  in  the 
flask  was  then  reduced  by  rarefying  the  air  by  means  of  a  method 
to  be  described  upon  another  occasion ;  and  for  each  difference  of 
pressure^,  measured  by  a  mercury  column,  the  number  of  seconds 
t  was  observed  which  a  given  quantity  of  water  occupied  in  passing 
through  the  filter.  The  following  are  the  results  : — 

I. 

p.  t.  pt. 

metre. 

0-179  91-7  16-4 

0-190  81-0  15-4 

0-282  52-9  14-9 

0-472  33-0  15-6 

In  the  ordinary  process  of  filtration,  p  on  the  average  amounts 
to  no  more  than  0-.004  to  0-008  metre.  The  advantage  gained, 
therefore,  is  easily  perceived  when  we  can  succeed  by  some  simple, 
practicable,  and  easily  attainable  method  in  multiplying  this  differ- 
ence in  pressure  one  or  two  hundred  times,  or,  say,  to  an  entire 
atmosphere,  without  running  any  risk  of  breaking  the  filter.  The 
solution  of  this  problem  is  very  easy :  an  ordinary  glass  funnel  has 
only  to  be  so  arranged  that  the  filter  can  be  completely  adjusted 
to  its  side  even  to  the  very  apex  of  the  cone.  For  this  purpose  a 
glass  funnel  is  chosen  possessing  an  angle  of  60°,  or  as  nearly  60° 
as  possible,  the  walls  of  which  must  be  completely  free  from  ine- 
qualities of  every  description;  and  into  it  is  placed  a  second 
funnel  made  of  exceedingly  thin  platinum-foil,  and  the  sides  of 


53,  a.]     BUNSEN'S  METHOD  OF  RAPID  FILTRATION . 


93 


which  possess  exactly  the  same  inclination  as  those  of  the  glass 
funnel.  An  ordinary  paper  filter  is  then  introduced  into  this  coin- 
pound  funnel  in  the  usual  manner ;  when  carefully  moistened  and 
so  adjusted  that  no  air-bubbles  are  visible  between  it  and  the  glass, 
this  filter,  when  filled  with  a  liquid,  will  support  the  pressure  of 
an  extra  atmosphere  without  ever  breaking. 


Fig.  43. 

The  platinum  funnel  is  easily  made  from  thin  platinum-foil  in 
the  following  manner : — In  the  carefully  chosen  glass  funnel  is 
placed  a  perfectly  accurately  fitting  filter  made  of  writing-paper; 
this  is  kept  in  position  by  dropping  a  little  melted  sealing-wax 
between  its  upper  edge  and  the  glass ;  the  paper  is  next  saturated 
with  oil  and  filled  with  liquid  plaster  of  Paris,  and  before  the 
mixture  solidifies  a  small  wooden  handle  is  placed  in  the  centre. 


94:  OPERATIONS.  [§  53,  a. 

After  an  hour  or  so  tlie  plaster  cone  with  the  adhering  paper 
filter  can  be  withdrawn  by  means  of  the  handle  from  the  funnel, 
to  which  it  accurately  corresponds.  The  paper  on  the  outside  of 
the  cone  is  again  covered  with  oil,  and  the  whole  carefully  inserted 
into  liquid  plaster  of  Paris  contained  in  a  small  crucible  4  or  5 
centims.  in  height.  After  the  mixture  has  solidified,  the  cone 
may  be  easily  withdrawn;  the  adhering  paper  filter  is  then 
detached,  and  any  small  pieces  of  paper  still  remaining  removed  by 
gentle  rubbing  with  the  linger.  In  this  manner  a  solid  cone  is  ob- 
tained accurately  fitting  into  a  hollow  cone,  and  of  which  the  angle 
of  inclination  perfectly  corresponds  with  that  of  the  glass  funnel. 

Fig.  43, 1,  represents  the  cones.     By  their  help  the  small  plati- 
num funnel  is  made.     A  piece  of  platinum  (shown  three-fourths 
of  the  natural  size  in  fig.  44)*  is  cut  from  foil  of 
such  a  thickness  that  one  square  centimetre  weighs 
|          /      about  O154  grm.,  and  from  the  centre  a  a  vertical 
5  incision  is  made  by  the  scissors  to  the  edge  c  I  <L 

Fig.  44.  rpjie  sma]i  piece  of  foil  is  next  rendered  pliable 
by  being  heated  to  redness,  and  is  placed  upon  the  solid  cone 
in  such  a  manner  that  its  centre  a  touches  the  apex  of  the 
latter ;  the  side  a  l>  d  is  then  closely  pressed  upon  the  plaster, 
and  the  remaining  portion  of  the  platinum  wrapped  as  equally 
and  as  closely  as  possible  around  the  cone.  On  again  heating  the 
foil  to  redness,  pressing  it  once  more  upon  the  cone,  and  inserting 
the  whole  into  the  hollow  cone,  and  turning  it  round  once  or 
twice  under  a  gentle  pressure,  the  proper  shape  is  completed. 
The  platinum  funnel,  which  should  not  allow  of  the  transmission 
of  light  through  its  extreme  point,  even  now  possesses  such  sta- 
bility that  it  may  be  immediately  employed  for  any  purpose.  If 
desired,  it  may  be  made  still  stronger  by  soldering  down  the  over- 
lapping portion  in  one  spot  only  to  the  upper  edge  of  the  foil  by 
means  of  a  grain  or  two  of  gold  and  borax ;  in  general,  however, 
this  precaution  is  unnecessary.  If  the  shape  has  in  any  degree 
altered  during  this  latter  process,  it  is  simply  necessary  to  drop 
the  platinum  funnel  into  the  hollow  cone  and  then  to  insert  the 
solid  cone,  when  by  one  or  two  turns  of  the  latter  the  proper  form 

*  The  diameter  of  a  in  the  original  drawing  is  2 '5  centimetres.  Perforated 
platinum  cones  admirably  adapted  for  use  with  the  BUNSEN  filtering  apparatus 
can  now  be  purchased  of  dealers  in  chemical  apparatus,  or  of  the  manufacturer, 
Mr.  J.  Bishop,  Sugartown,  Chester  Co.,  Pa. 


§  53,  a.]    BUNSEN'S  METHOD  OF  RAPID  FILTRATION.  95 

may  be  immediately  restored.  The  platinum  funnel  is  placed  in 
the  bottom  of  the  glass  funnel,  the  dry  paper  filter  then  introduced 
in  the  ordinary  manner,  moistened,  and  freed  from  all  adhering 
air-bubbles  by  pressure  with  the  finger.  A  filter  so  arranged  and 
in  perfect  contact  with  the  glass,  when  filled  with  a  liquid  will 
support  the  pressure  of  an  entire  atmosphere  without  the  least 
danger  of  breaking ;  and  the-  interspace  between  the  folds  of  the 
platinum  foil  is  perfectly  sufficient  to  allow  of  the  passage  of  a 
continuous  stream  of  water. 

In  order  to  be  able  to  produce  the  additional  pressure  of  an 
atmosphere,  the  filtered  liquid  is  received  in  a  strong  glass  flask 
instead  of  in  beakers.*  This  flask  is  closed  by  means  of  a  doubly 
perforated  caoutchouc  cork,  through  one  of  the  holes  of  which  the 
neck  of  the  glass  funnel  is  passed  to  a  depth  oifrmn  5  to  8  ceht't- 
n Litres  (tig.  43,  #);  through  the  other  is  fitted  a  narrow  tube  open 
at  both  ends,  the  lower  end  of  which  is  brought  exactly  to  ///> 
len-l  of  the  lowrr  surface  of  the  cork*  to  the  other  is  adapted  the 
caoutchouc  tube  connected  with  the  apparatus  destined  to  produce 
the  requisite  difference  in  pressure :  this  apparatus  will  be  de- 
scribed immediately.  The  flasks  are  placed  in  a  metallic  or  porce- 
lain vessel,  in  the  conical  contraction  of  wdiich  several  strips  of 
cloth  are  fastened.  This  method  of  supporting  the  flask  has  the 
advantage  that,  in  one  and  the  same  vivsi-1,  tlasks  varying  in  size 
from  0'5  to  2*5  litres  stand  equally  weP  <*nd  that  by  simply  laying 
a  cloth  over  the  mouth  of  the  vesse/,  the  consequences  of  an 
explosion  (which  through  inexperience  or  carelessness  is  possible) 
are  rendered  harmless. 

It  is  impossible  to  employ  any  of  the  air-pumps  at  present  in 
use  to  create  the  difference  in  pressure,  since  the  filtrate  not  unfre- 
quently  contains  chlorine,  sulphurous  acid,  hydric  sulphide,  and 
other  substances  which  would  act  injuriously  upon  the  metallic 
portions  of  these  instruments.  I  therefore  employ  a  water  air- 
pump  constructed  on  the  principle  of  SPRENGEL'S  mercury-pump, 
and  which  appears  to  me  preferable  to  all  other  forms  of  air-pump 
for  chemical  purposes,  since  it  effects  a  rarefaction  to  within  6  or 
12  millimetres  pressure  of  mercury. 

Fig.  43  shows  the  arrangement  of  this  pump.  On  opening  the 
pinch-cock  </,  water  flows  from  the  tube  I  into  the  enlarged  glass 

*  These  flasks  must  be  somewhat  thicker  than  those  ordinarily  used,  in  order 
to  prevent  the  possibility  of  thair  giving  way  under  the  atmospheric  pressure. 


96  OPERATIONS.  [§  53,  a. 

vessel  J,  and  thence  down  the  leaden  pipe  c.  This  pipe  has  a 
diameter  of  about  8  millims.,  and  extends  downward  to  a  depth  of 
30  or  40  feet,  and  ends  in  a  sewer  or  other  arrangement  serving  to 
-convey  the  water  away.  The  lower  end  of  the  tube  d  possesses  a 
narrow  opening ;  it  is  hermetically  sealed  into  the  wider  tube  6, 
-and  reaches  nearly  to  the  bottom  of  the  latter.  A  manometer  is 
.attached  to  the  upper  continuation  of  this  tube  d  by  means  of  a 
side  tube  at  d1 ;  at  d?  is  attached  a  strong  thick  caoutchouc  tube 
possessing  an  internal  diameter  of  5  millims.  and  an  external  diam- 
eter of  12  millims. ;  this  leads  to  the  flask  which  is  to  be  rendered 
vacuous,  and  is  connected  with  it  by  means  of  the  short  narrowed 
tube  k.  Between  the  air-pump  and  the  flask  is  placed  the  small 
thick  glass  vessel/1,  in  which,  when  one  washes  with  hot  water,  the 
steam  which  may  be  carried  over  is  condensed.  All  the. caoutchouc 
joinings  are  made  with  very  thick  tubing,  the  internal  diameter  of 
which  amounts  to  about  5  millims.,  the  external  diameter  to  about 
17  millims.  The  entire  arrangement  is  screwed  down  upon  a 
board  fastened  to  the  wall,  in  such  a  manner  that  each  separate 
piece  of  the  apparatus  is  held  by  a  single  fastening  only,  in  order 
to  prevent  the  tubes  being  strained  and  broken  by  the  possible 
warping  of  the  board.  On  releasing  the  pinchcock  «,  water  flows 
from  the  conduit  Z  down  the  tube  c  to  a  depth  of  more  than  30 
feet,  carrying  with  it  the  air  which  it  sucks  through  the  small 
opening  of  the  tube  d  in  the  form  of  a  continuous  stream  of 
bubbles.  No  advantage  is  gained  by  increasing  the  rapidity  of 
the  flow,  since  the  friction  exerted  by  the  water  upon  the  sides  of 
the  leaden  pipe  acts  directly  as  a  counter-pressure,  and  a  compara- 
tively small  increase  in  the  rapidity  of  the  flow  is  accompanied  by 
a  great  increase  in  the  amount  of  this  friction.  Accordingly  at  g 
is  a  second  pinchcock,  by  which  the  stream  can  be  once  for  all  so 
regulated  that,  on  completely  opening  the  cock  #,  the  friction,  on 
account  of  the  diminished  rate  of  flow,  is  rendered  sufficiently 
small  to  allow  of  the  maxim  urn  degree  of  rarefaction.  Such  an 
apparatus,  when  properly  regulated  once  for  all  by  means  of  the 
cock  </,  exhausts  in  a  comparatively  short  time  the  largest  vessels 
to  within  a  pressure  of  mercury  equal  to  the  tension  of  aqueous 
vapor  at  the  temperature  possessed  by  the  stream.*  The  tension 

*  The  time  required  to  obtain  the  above  degree  of  exhaustion  in  a  flask  of 
from  1  to  3  litres  capacity  ranges  from  six  to  ten  minutes ;  the  quantity  of  water 
necessary  amounts  to  about  40  or  50  litres. 


§  53,  b.]    BUNSEN'S  METHOD  OF  RAPID  FILTRATION.  97 

exerted  by  the  water-stream  in  my  laboratory,  in  which  six  of 
these  pumps  are  used,  amounts  to  about  7  millims.  in  winter  and 
10  millims.  in  summer.  The  filtration  is  made  in  the  following 
manner:  The  flask  standing  in  the  metallic  or  porcelain  vessel  is 
connected  by  means  of  the  slightly  drawn-out  tube  Jc  with  the 
caoutchouc  tube  h  attached  to  the  pump,  the  cock  a  having  been 
previously  opened  and  the  properly  fitted  moistened  filter  filled 
with  the  liquid  to  be  filtered.  As  usual,  the  clear  supernatant 
fluid  is  first  poured  upon  the  filter;  in  a  moment  or  two  the 
filtrate  runs  through  in  a  continuous  stream,  often  so  rapidly  that 
one  must  hasten  to  keep  up  the  supply  of  liquid,  since  it  is  advis- 
able to  maintain  the  filter  as  full  as  possible.  After  the  precipi- 
tate has  been  entirely  transferred,  the  filtrate  passes  through  drop 
by  drop,  and  the  manometer  not  unfrequently  now  shows  a  pres- 
sure of  an  extra  atmosphere.  The  filter  may  be  filled  (in  fact  this 
is  to  be  recommended)  with  the  precipitate  to  within  a  millimetre 
of  its  edge,  since  the  precipitate,  in  consequence  of  the  high  pres- 
sure to  which  it  is  subjected,  becomes  squeezed  into  a  thin  layer 
broken  up  by  innumerable  fissures.  As  soon  as  the  liquid  has 
passed  through  and  the  first  traces  of  this  breaking  up  become 
evident,  the  precipitate  will  be  found  to  have  been  so  firmly 
pressed  upon  the  paper,  that  on  cautiously  pouring  water  over  it  it 
remains  completely  undisturbed.  The  washing  is  effected  by  care- 
fully pouring  water  down  the  side  of  the  funnel  to  within  a  centi- 
metre above  the  rim  of  the  filter :  the  washing  flask  for  this  pur- 
pose is  not  applicable ;  the  water  must  be  poured  from  an  open 
vessel.  After  the  filter  has  in  this  manner  been  replenished  four 
times  with  water  and  allowed  to  drain  for  a  few  minutes,  it  will 
be  found  to  be  already  so  far  dried,  in  consequence  of  the  high 
pressure  to  which  it  has  been  subjected,  that  without  any  further 
desiccation  it  may  be  withdrawn,  together  with  the  precipitate, 
from  the  funnel,  and  immediately  ignited,  with  the  precautions  to 
be  presently  given,  in  the  crucible. 

§  53,  b. 
BUNSEN'S  SIMPLIFIED  EXHAUSTING  APPARATUS. 

It  is  not  necessary  to  use  a  pump  as  powerful  as  that  described, 
since  a  fall  of  10  or  15  feet  is  sufficient  to  filter  a  precipitate  accord- 
ing to  the  above  described  method,  and  so  far  to  dry  it  that  it  can 


98 


OPERATIONS. 


[§  53,  c. 


be  immediately  ignited  in  the  crucible.  The  simple  arrangement 
represented  in  iig.  45  answers  this  purpose.  It  consists  of  two 
equal-sized  bottles,  a  and  a',  of  from  2  to  4  litres  capacity,  each  of 
which  is  provided  near  the  bottom  with  a  small  stopcock  designed 
to  regulate  the  flow  of  water.  Suppose  a 
filled  with  water  and  placed  upon  a  shelf  as 
high  above  the  ground  as  possible,  and  af 
placed  empty  on  the  floor,  and  the  two  stop- 
-  cocks  connected  by  means  of  caoutchouc  tub- 
ing c,  then  on  allowing  water  to  flow  down 
the  tube  the  air  in  the  upper  bottle  becomes 
somewhat  rarefied  ;  and  in  order  to  employ 
the  consequent  difference  in  pressure  (amount- 
ing to  a  column  of  mercury  about  0*2  metre 
in  height)  for  the  purpose  of  filtration,  it  is 
only  necessary  to  connect  the  mouth  of  the 
upper  bottle  with  the  tube  of  the  filter-flask. 
"When  the  water  has  ceased  to  flow,  the  posi- 
tion of  the  bottle  is  reversed,  when  the  oper- 
ation recommences.  So  small  a  pressure  as 
0*2  metre  suffices  to  render  the  filter  and  its 
contents  so  far  dry  that  they  may  be  imme- 
diately withdrawn  from  the  funnel  and  ig- 
nited without  any  other  preliminary  desicca- 
tion. 

§  53,  c. 

BUNSEN'S  METHOD  OF  DRYING  AND  IGNITING 
PRECIPITATES. 


Fig.  45. 


If  a  precipitate  be  heated  in  a  platinum 
crucible  immediately  after  filtration  by  the 
older  process,  a  portion  will  inevitably  be 
projected  out  of  the  crucible.  Hitherto,  therefore,  it  has  been 
necessary  to  dry  the  filter  and  precipitate  before  ignition.  ~Now 
to  dry  a  quantity  of  hydrated  chromium  sesquioxide  containing 
0-2436  grin.  Cr2O3  in  a  water-bath  at  100°  C.  requires  at  least  five 
hours;  and,  moreover,  bringing  the  dried  precipitate  into  the 
crucible,  burning  the  filter,  and  gradually  igniting  the  mass  is  in 
the  highest  degree  tedious  and  troublesome.  All  this  expenditure 


§  53,  c.]    BUNSEN'S  METHOD  OF  IGNITING  PRECIPITATES.    99 

of  time  and  labor  may  be  saved  by  employing  the  new  method. 
By  its  means  a  precipitate  is  as  completely  dried  upon  the  filter  in 
from  1  to  5  minutes  as  if  it  had  been  exposed  from  5  to  8  hours  in 
a  drying  chamber  ;  and  it  can  immediately,  filter  and  all,  be  thrown 
into  a  platinum  or  porcelain  crucible  and  ignited  without  the  slight- 
est fear  of  its  spurting.  By  operating  in  the  following  manner  the 
filter  burns  quietly  without  flame  or  smoke;  this  phenomenon, 
although  remarkable,  easily  admits  of  an  explanation.  The  portion 
of  filter-paper  free  from  precipitate  is  tightly  wrapped  round  the 
remainder  of  the  filter  in  such  a  manner  that  the  precipitate  is 
enveloped  in  from  four  to  six  folds  of  clean  paper.  The  whole  is 
then  dropped  into  the  platinum  or  porcelain  crucible  lying  obliquely 
upon  a  triangle  over  the  lamp,  and  pushed  down  against  its  sides 
with  the  finger.  The  cover  is  then  supported  against  the  mouth  of 
the  crucible  in  the  ordinary  way,  and  the  ignition  commenced  by 
heating  the  portion  of  the  crucible  in  contact  with  the  cover.  When 
the  flame  has  the  proper  size  and  position,  the  filter  carbonizes 
quietly  without  any  appearance  of  flame  or  considerable  amount  of 
smoke.  When  the  carbonization  proceeds  too  slowly,  the  flame  is 
moved  a  little  toward  the  bottom  of  the  crucible.  After  some  time 
the  precipitate  appears  to  be  surrounded  only  by  an  extremely  thin 
envelope  of  carbon,  possessing  exactly  the  form  (of  course  dimin- 
ished in  size)  of  the  original  filter;  the  flame  is  then  increased,, 
and  the  crucible  maintained  at  a  bright-red  heat  until  the  carbon 
contained  in  this  envelope  is  consumed.  The  combustion  proceeds 
so  quietly  that  the  resulting  ash  surrounding  the  precipitate  pos- 
sesses, even  to  the  smallest  fold,  the  exact  form  of  the  original 
filter.  If  the  ash  shows  here  and  there  a  dark  color,  it  is  simply 
necessary  to  heat  the  crucible  over  a  blast-lamp  for  a  few  minutes 
to  effect  the  complete  removal  of  the  trace  of  carbon.  This 
method  of  burning  a  filter  is  extremely  convenient  and  accurate  ; 
it  is  only  necessary  to  give  a  little  attention  at  first  to  the  slow  car- 
bonization of  the  paper,  after  which  the  further  progress  of  the 
operation  may  be  left  to  itself. 

Gelatinous,  finely  divided,  granular,  and  crystalline  precipitates, 
such  as  alumina,  calcium  oxalate,  barium  sulphate,  silica,  &c.,  may 
with  equal  facility  be  treated  in  this  manner ;  so  that  even  in  this 
particular  the  work,  in  comparison  with  the  method  generally 
adopted,  is  considerably  shortened  and  simplified.  [This  method 
should  not,  of  course,  be  used  when  the  substance  to  be  ignited  is 


100 


OPERATIONS. 


[§  53,  d. 


such  as  to  be  injuriously  affected  by  the  reducing  action  of  filter- 
paper.] 

§  53,  d. 
USE  OF  ASBESTOS  FILTERS  WITH  BUNSEN' s  FILTERING  APPARATUS. 

A  method  of  filtering,  washing,  and  igniting  precipitates  with 
out  the  use  of  paper  filters,  which  in  many  cases  possesses  great 
advantages,  has  been  devised  by  F.  A.  GOOCH, 
and  is  described    as    follows.*     First.  White, 
silky,  anhydrous  asbestos  is  scraped  to  a  fine 
short  down  with  an  ordinary  knife-blade,  boiled 
with  hydrochloric  acid  to  remove  traces  of  iron 
or   other  soluble  matter,  washed  by  decantation,   and  set  aside 
for  use. 

Secondly.  A  platinum  crucible  of  ordinary  size,  preferably  of 
the  broad  low  pattern  (fig.  46),  is  chosen,  and  the  bottom  (fig.  47) 
perforated  with  fine  holes  (the  more 
numerous  aiid  the  finer  the  better) 
by  means  of  a  steel  point ;  or  better 
still,  the  bottom  may  be  made  of  fine 
platinum  gauze.  Next,  a  Bunsen  fun- 
nel of  the  proper  size  is  selected,  and  over  the 
top  a  short  piece  of  rubber  tubing  f  is  stretched 
and  drawn  down  until  the  portion  above  the 
funnel  arranges  itself  at  right  angles  to  the 
stem.  "Within  the  opening  in  the  rubber,  the 
perforated  crucible  is  fitted  as  shown  in  fig.  48, 
and  the  funnel  is  connected  with  the  receiver 
of  a  Bunsen  pump  or  other  exhausting  appa- 
ratus in  the  ordinary  way. 

To  make  the  asbestos  filter,  the  pressure  of  the  pump  is  applied, 
and  a  little  of  the  asbestos  prepared  as  described,  and  suspended  in 
water,  is  poured  into  the  crucible.  The  rubber  and  the  crucible 

*  Proceedings  of  Am.  Acad.  Arts  and  Sciences,  1878,  p.  342. 

f  If  suitable  rubber  tubing  is  not  at  hand  for  fitting  the  crucible  to  the  fun- 
nel, a  piece  of  strong  glass  tube,  preferably  tapering  slightly,  may  be  used  in 
place  of  a  funnel.  The  diameter  of  the  tube  should  exceed  that  of  the  crucible. 
One  end  is  drawn  down  to  size  of  a  common  funnel  stem;  the  crucible  is  then 
fitted  to  the  large  end  by  means  of  a  short  section  of  large  rubber  tubing,  or  a 
bored  rubber  stopper. 


Fig.  47. 


Fig.  48. 


§53,  d.]  GOOCH'S  METHOD  OF  FILTRATION  AND  IGNITION.    101 

are  held  together  bj  the  exhaustion  of  the  vacuum  pump  with  suf- 
ficient force  to  make  an  air-tight  joint ;  the  water  is  drawn  through 
and  the  asbestos  is  deposited  almost  instantly  in  a  close  compact 
layer  on  the  perforated  bottom ;  more  asbestos  (if  necessary)  in  sus- 
pension as  before  being  poured  upon  the  first  until  the  layer 
becomes  sufficiently  thick  for  the  purpose  for  which  it  is  intended. 
Finally  a  little  distilled  water  is  drawn  through  the  apparatus  to 
wash  away  any  filaments  which  might  cling  to  the  under  side,  and 
the  filter  is  ready  for  use ;  the  whole  process  occupying  less  time 
than  is  required  to  fold  and  fit  an  ordinary  paper  filter  to  a  funnel. 

To  prepare  the  filter  for  the  weighing  of  a  precipitate,  the 
crucible  with  the  felt  of  asbestos  undisturbed  is  removed  from 
the  funnel  and  ignited.  In  case  the  precipitate  to  be  subse- 
quently collected  must  be  heated  to  high  temperature  for  a  long 
time,  it  is  better  to  enclose  the  perforated  crucible  with  its  felt 
within  another  crucible ;  because  in  such  cases  asbestos  felt  is  apt 
to  curl  at  the  edges,  and  without  such  precaution  some  of  the 
precipitate  might  drop  through  the  perforations  and  be  lost.  For 
drying  at  low  temperatures,  however,  and  even  for  ordinary  igni- 
tion, a  second  crucible  is  unnecessary ;  but,  during  the  ignition  of 
an  easily  reducible  substance  care  must  be  taken  to  avoid  contact 
of  unburnt  gas  with  the  perforated  bottom. 

To  perform  the  filtration,  the  crucible  is  replaced  in  the  funnel, 
the  pressure  applied,  and  the  process  conducted  precisely  as  in 
ordinary  filtration  by  the  Bunsen  pump.  It  is  necessary  to  observe 
that  the  vacuum  pump  be  started  before  pouring  the  liquid  upon 
the  filter.  The  final  drying  or  ignition,  as  the  case  may  be,  of  the 
precipitate  and  filter  is  made  without  difficulty,  or  need  of  extra 
precaution. 

For  turbid  liquids,  or  gelatinous  precipitates,  instead  of  the 
perforated  crucible  a  platinum  cone  may  be  used,  the  upper  part 
being  made  of  foil,  the  lower  part  of  gauze.  This  process  is  recom- 
mended not  only  for  such  precipitates  as  have  heretofore  usually 
been  collected  upon  weighed  paper  filters,  but  also  for  many  other 
precipitates  which  are  usually  ignited,  but  whose  proper  ignition 
is  more  or  less  interfered  with  by  the  presence  of  carbon. 


102  OPERATIONS.  [§  54. 


5.  ANALYSIS  BY  MEASURE  (VOLUMETEIC  ANALYSIS). 

The  principle  of  volumetric  analysis  has  been  explained  already 
in  the  "  Introduction,"  where  we  have  seen  how  the  quantity  of 
iron  present  in  a  fluid  as  a  ferrous  salt  may  be  determined  by  means 
of  a  solution  of  potassium  permanganate,  the  value  of  which  has 
been  previously  ascertained  by  observing  the  quantity  required  to 
convert  a  known  amount  of  iron  from  a  ferrous  to  a  ferric  salt. 

Solutions  of  accurately  known  composition  or  strength,  used  for 
the  purposes  of  volumetric  analysis,  are  called  standard  solutions. 
They  may  be  prepared  in  two  ways,  viz.,  (a)  by  dissolving  a 
weighed  quantity  of  a  substance  in  a  definite  volume  of  fluid  ;  or 
(5),  by  first  preparing  a  suitably  concentrated  solution  of  the  reagent 
required,  and  then  determining  its  exact  strength  by  a  series  of 
experiments  made  with  it  upon  weighed  quantities  of  the  body 
for  the  determination  of  which  it  is  intended  to  be  used. 

In  the  preparation  of  standard  solutions  by  method  «,  the  weight 
of  the  reagent  taken  for  1000  c.c.  may,  if  desired,  be  a  weight 
exactly  equivalent  to  1  gramme  of  hydrogen  (see  §  192,  c9  tf).  In 
the  case  of  standard  solutions  prepared  by  method  J,  this  may  also 
be  easily  done,  by  diluting  to  the  required  degree  the  still  some- 
what too  concentrated  solution,  after  having  accurately  determined 
its  strength  ;  however,  as  a  rule,  this  latter  process  is  only  resorted 
to  in  technical  analyses,  where  it  is  desirable  to  avoid  all  calculation. 
Fluids  which  contain  the  eq.  number  of  grammes  of  a  substance  in 
one  litre,  are  called  normal  solutions  ;  those  which  contain  -£$  of 
this  quantity,  decinormal  solutions. 

The  determination  of  a  standard  solution  intended  to  be  used 
for  volumetric  analysis  is  obviously  a  most  important  operation  ; 
since  any  error  in  this  will,  of  course,  necessarily  falsify  every 
analysis  made  with  it.  In  scientific  and  accurate  researches  it  is, 
therefore,  always  advisable,  whenever  practicable,  to  examine  the 
standard  solution  —  no  matter  whether  prepared  by  method  #,  or 
by  method  J,  with  subsequent  dilution  to  the  required  degree  —  by 
experimenting  with  it  upon  accurately  weighed  quantities  of  the 
body  for  the  determination  of  which  it  is  to  be  used. 

In  the  previous  remarks  I  have  made  no  difference  between 
fluids  of  known  composition  and  those  of  known  power  ;  and  this 


§54.]  VOLUMETRIC   ANALYSIS.  103 

has  hitherto  been  usual.  But  by  accepting  the  two  expressions 
as  synonymous,  we  take  for  granted  that  a  fluid  exercises  a  chemi- 
cal action  exactly  corresponding  to  the  a'mount  of  dissolved  sub- 
stance it  contains — that,  for  instance,  a  solution  of  sodium  chloride 
containing  1  inol.  Na  01  will  precipitate  exactly  1  at.  silver.  This 
presumption,  however,  is  very  often  not  absolutely  correct,  as  will 
be  shown  with  reference  to  this  very  example,  §  115,  J,  5.  In  such 
cases,  of  course,  it  is  not  merely  advisable,  but  even  absolutely 
necessary,  to  determine  the  strength  of  the  fluid  by  experiment, 
although  the  amount  of  the  reagent  it  contains  may  be  exactly 
known,  for  the  power  of  the  fluid  can  be  inferred  from  its  com- 
position only  approximately  and  not  with  perfect  exactness.  If  a 
standard  solution  keeps  unaltered,  this  is  a  great  advantage,  as  it 
dispenses  with  the  necessity  of  determining  its  strength  before 
every  fresh  analysis. 

That  particular  change  in  the  fluid  operated  upon  by  means  of 
a  standard  solution  which  marks  the  completion  of  the  intended 
decomposition,  is  termed  the  FINAL  REACTION.  This  consists  either 
in  a  change  of  color,  as  is  the  case  when  a  solution  of  potassium  per- 
manganate acts  upon  an  acidified  solution  of  ferrous  salt,  or  a  solu- 
tion of  iodine  upon  a  solution  of  sulphuretted  hydrogen  mixed  with 
starch  paste ;  or  in  the  cessation  of  the  formation  of  a  precipitate 
upon  further  addition  of  the  standard  solution,  as  is  the  case  when 
a  standard  solution  of  sodium  chloride  is  used  to  precipitate  silver 
from  its  solution  in  nitric  acid;  or  in  incipient  precipitation,  as  is 
the  case  when  a  standard  solution  of  silver  is  added  to  a  solution  of 
hydrocyanic  acid  mixed  with  an  alkali ;  or  in  a  change  in  the  action 
of  the  examined  fluid  upon  a  particular  reagent,  as  is  the  case 
when  a  solution  of  sodium  arsenite  is  added,  drop  by  drop,  to  a 
solution  of  chloride  of  lime,  until  the  mixture  no  longer  imparts  a 
blue  tint  to  paper  moistened  with  potassium  iodide  and  starch- 
paste,  &c. 

The  more  sensitive  a  final  reaction  is,  and  the  more  readily,  posi- 
tively, and  rapidly  it  manifests  itself,  the  better  is  it  calculated  to 
serve  as  the  basis  of  a  volumetric  method.  In  cases  where  it  is  an 
object  of  great  importance  to  ascertain  with  the  greatest  practica- 
ble precision  the  exact  moment  when  th*e  reaction  is  completed,  the 
analyst  may  sometimes  prepare,  besides  the  actual  standard  solu- 
tion, another,  ten  times  more  dilute,  and  use  the  latter  to  finish  the 
process,  carried  nearly  to  completion  with  the  former. 


104  OPERATIONS.  [§   54. 

But  a  good  final  reaction  is  not  of  itself  sufficient  to  afford  a  safe 
basis  for  a  good  volumetric  method  ;  this  requires,  as  the  first  and 
most  indispensable  condition,  that  the  particular  decomposition 
which  constitutes  the  leading  point  of  the  analytical  process  should 
— at  least  under  certain  known  circumstances — remain  unalterably 
the  same.  Wherever  this  is  not  the  case — where  the  action  varies 
with  the  greater  or  less  degree  of  concentration  of  the  fluid,  or 
according  as  there  may  be  a  little  more  or  less  free  acid  present ;  or 
according  to  the  greater  or  less  rapidity  of  action  of  the  standard 
solution  ;  or  where  a  precipitate  formed  in  the  course  of  the  process 
has  not  the  same  composition  throughout  the  operation — the  basis 
of  the  volumetric  method  is  fallacious,  and  the  method  itself, 
therefore,  of  no  value. 


SECTION    II. 
REAGENTS. 

§  55. 

FOR  general  information  respecting  reagents,  I  refer  the  stu- 
dent to  my  volume  on  "  Qualitative  Analysis." 

The  instructions  given  here  will  be  confined  to  the  preparation, 
testing,  and  most  important  uses  of  those  chemical  substances  which 
subserve  principally  and  more  exclusively  the  purposes  of  quanti- 
tative analysis.  Those  reagents  which  are  employed  in  qualitative 
investigations,  having  been  treated  of  already  in  the  volume  on  the 
qualitative  branch  of  the  analytical  science,  will  therefore  be  simply 
mentioned  here  by  name. 

The  reagents  used  in  quantitative  analysis  are  properly  arranged 
under  the  following  heads  : — 

A.  Reagents  for  gravimetric  analysis  in  the  wet  way. 

B.  Reagents  for  gravimetric  analysis  in  the  dry  way. 

C.  Reagents  for  volumetric  analysis. 

D.  Reagents  used  in  organic  analysis. 

The  mode  of  preparing  the  fluids  used  in  volumetric  analysis, 
will  be  found  where  we  shall  have  occasion  to  speak  of  their  appli- 
cation. 

A.  REAGENTS  FOR  GRAVIMETRIC  ANALYSIS  IN  THE  WET  WAY. 
I.     SIMPLE    SOLVENTS. 

§56. 
1.  DISTILLED  WATER  (see  "  Qual.  Anal."). 

Water  intended  for  quantitative  investigations  must  be  perfectly 
pure.  Water  distilled  from  glass  vessels  leaves  a  residue  upon 
evaporation  in  a  platinum  vessel  (see  experiment  No.  5),  and  is 
therefore  inapplicable  for  many  purposes  ;  as,  for  instance,  for  the 
determination  of  the  exact  degree  of  solubility  of  sparingly  soluble 


10.6  OPERATIONS.  [§  57 

substances.     For  certain  uses  it  is  necessary  to  free  the  water  by 
ebullition  from  atmospheric  air  and  carbonic  acid. 

2.  ALCOHOL  (see  "  Qual.  Anal."). 

a.  Absolute  alcohol.     Z>.  Common  alcohol  of  various  degrees  of 
strength. 

3.  ETHEK. 

The  application  of  ether  as  a  solvent  is  very  limited.  It  is 
more  frequently  used  mixed  with  alcohol,  in  order  to  diminish  the 
solvent,  power  of  the  latter  for  certain  substances,  e.g.,  ammonium 
platinic  chloride.  The  ordinary  ether  of  the  shops  will  answer  the 
purpose. 

4.  CARBON  BISULPHIDE  (see  "  Qual.  Anal."). 

II.    ACIDS  AND  HALOGENS. 

a.  Oxygen  Acids. 


1.  SULPHURIC  ACID. 

a.  Concentrated  sulphuric  acid  of  the  shops. 
J.  Concentrated  pure  sulphuric  acid. 
c.  Bilute  sulphuric  acid. 

See  "Qual.  Anal." 

2.  NITRIC  ACID. 

a.  Pure  nitric  acid  of  1-2  sp.  gr.  (see  "  Qual.  Anal."). 

J.  Red  fuming  nitric  acid  (concentrated  nitric  acid  containing 
some  hyponitric  acid). 

Preparation.  —  Two  parts  of  pure,  dry  potassium  nitrate  are 
introduced  into  a  capacious  retort,  and  one  part  of  concentrated 
sulphuric  acid  is  added  either  through  the  tubulure  of  the  retort, 
or  if  a  common  non-tubulated  one  is  used,  through  the  neck  by 
means  of  a  long  funnel-tube  bent  at  the  lower  end,  carefully  avoid- 
ing soiling  the  neck  of  the  retort.  The  latter  being  put  into  a  ves- 
sel filled  with  sand,  or,  better  still,  with  iron  turnings,  is  then  con- 
nected with  a  receiver,  but  not  quite  aiivtight.  The  distillation  is 
conducted  at  a  gradually  increased  heat,  and  carried  to  dryness. 
The  cooling  of  the  receiver  must  be  properly  attended  to  during 
the  distillation.  In  the  preparation  of  small  quantities,  the  retort 


§  58.]  REAGENTS.  107 

is  placed  on  a  piece  of  wire-gauze,  and  heated  with  charcoal ;  in 
this  process  it  is  always  advisable  to  coat  the  retort  by  repeated 
application  of  a  thin  paste  made  of  clay  and  water ;  a  little  borax 
or  sodium  carbonate  should  be  added  to  the  water  used  for  making 
the  paste. 

Tests. — Red  fuming  nitric  acid  must  be  in  a  state  of  the  greatest 
possible  concentration,  and  perfectly  free  from  sulphuric  acid.  In 
order  to  detect  minute  traces  of  the  latter,  evaporate  a  few  c.  c.  of 
the  specimen  in  a  porcelain  dish  nearly  to  dryness,  dilute  the  resi- 
due with  water,  add  some  barium  chloride,  and  observe  whether  a 
precipitate  forms  on  standing. 

Uses. — A  powerful  oxidizing  agent  and  solvent ;  it  serves  more 
especially  to  convert  sulphur  and  metallic  sulphides  into  sulphuric 
acid  and  sulphates  respectively. 

3.  ACETIC  ACID  (see  "  Qual.  Anal."). 

4.  TARTARIC  ACID  (see  "  Qual.  Anal."). 

b.  Hydrogen  Acids  and  Hologens. 

§58. 
1.  HYDROCHLORIC  Aero. 

a.  Pure  hydrochloric  acid  of  1*12  sp.  gr.  (see  "Qual.  Anal."). 

b.  Pure  fuming  hydrochloric  acid  of  about  1*18  sp.  gr. 

Preparation. — As  in  "  Qual.  Anal."  §  26,  with  this  modifica- 
tion, however,  that  only  3  or  4  parts  of  water,  instead  of  6,  are  put 
into  the  receiver,  to  4  parts  of  sodium  chloride  in  the  retort.  The 
greatest  care  must  be  taken  to  keep  the  receiver  cool,  and  to  change 
it  as  soon  as  the  tube  through  which  the  gas  is  conducted  into  it- 
begins  to  get  hot,  since  it  is  now  no  longer  hydrochloric  acid  gas 
which  passes  over,  but  an  aqueous  solution  of  the  gas,  in  form  of 
vapor,  which  would  simply  weaken  the  fuming  acid,  if  it  were 
allowed  to  mix  with  it. 

Tests. — The  fuming  acid  must,  for  many  purposes,  be  perfectly 
free  from  chlorine  and  sulphurous  acid.  For  the  mode  of  testing 
for  these  impurities,  see  "  Qual  Anal."  loc.  cit.  Test  for  sulphuric 
acid  as  under  Nitric  Acid,  above. 

Uses. — Fuming  hydrochloric  acid  has  a  much  more  energetic 
action  than  the  dilute  acid ;  it  is,  therefore,  used  instead  of  the 
latter  in  cases  where  a  more  rapid  and  energetic  action  is  desirable. 


108  KEAGENTS.  [§  58. 

2.  HYDROFLUORIC  ACID. 

This  is  employed  for  the  decomposition  of  silicates  and  borates, 
sometimes  in  the  gaseous  form,  sometimes  in  the  condition  of 
aqueous  solution.  In  the  first  case,  the  substance  to  be  decomposed 
is  introduced  into  the  leaden  box,  in  which  the  hydrofluoric  gas  is 
being  generated ;  in  the  latter  case,  we  must  first  prepare  the  aque- 
ous acid.  The  raw  material  employed  is  fluor  spar  or  kryolite 
(LUBOLDT*).  Both  are  first  finely  powdered,  and  then  treated  with 
concentrated  sulphuric  acid.  To  1  part  kryolite,  2-J  parts  sulphuric 
acid  are  used ;  to  1  part  fluor  spar,  2  parts  sulphuric  acid  are 
used.  If  the  latter  is  employed,  allow  the  mixture  to  stand  in 
a  dry  place  for  several  days,  stirring  every  now  and  then,  so  that 
the  silicic  acid  (which  is  generally  contained  in  fluor  spar)  may 
first  escape  in  the  form  of  fluosilicic  gas.  Convenient  distil- 
latory apparatus  have  been  described  by  LUBOLDT  (loc.  cit.)  and  by 
H.  BRiEGLEB.f  The  latter  commends  itself  especially  on  account 
of  its  relatively  small  cost.  It  consists  of  a  leaden  retort,  with  a 
movable  leaden  top,  which  can  be  luted  on.  The  receiver  belong- 
ing to  it  is  a  box  of  lead,  with  a  tubulure  at  the  side,  into  which 
the  neck  of  the  retort  just  enters.  The  cover  of  the  receiver  is 
raised  conical,  and  is  provided  at  the  top  with  an  exit  tube  of  lead. 
In  the  receiver  a  platinum  dish  containing  water  is  placed,  all 
joints  are  luted,  and  the  retort  is  carefully  heated  in  a  sand-bath. 
The  aqueous  hydrofluoric  acid  found  at  the  end  of  the  operation  in 
the  platinum  dish  is  perfectly  pure.  The  small  quantity  of  impure 
hydrofluoric  acid  which  collects  on  the  bottom  of  the  receiver  is 
thrown  away.  The  hydrofluoric  acid  must  entirely  volatilize  when 
heated  in  a  platinum  dish  on  a  water-bath.  The  pure  acid  gives  no 
precipitate  when  neutralized  with  potash,  while  potassium  silico- 
fluoride  separates  if  the  acid  contains  hydrofluosilicic  acid.  The 
acid  is  best  preserved  in  gutta-percha  bottles,  as  recommended  by 
STADELER.  The  greatest  caution  must  be  observed  in  preparing 
this  acid,  since,  whether  in  the  fluid  or  gaseous  condition,  it  is  one 
of  the  most  injurious  substances. 

3.  CHLORINE  AND  CHLORINE-WATER  (see  "  Qual.  Anal"). 

4.  NITRO-HYDROCHLORIC  ACID  (see  "  Qual.  Anal."). 

5.  HYDROFLUOSILICIC  ACID  (see  "  Qual.  Anal."). 

*  Journ.  furprakt.  Chem.,  76/330. 
f  Annal.  d.  Chem.  u.  Pharm.,  Ill,  380. 


§  59.]  REAGENTS.  109 

c.  Sulphur  Acids. 
1.  HYDROSULPHURIC  ACID  (see  "  Qual.  Anal."). 

HI.  BASES  AND  METALS. 
a.  Oxygen  Bases  and  Metals. 

§  59. 
a.  Alkali  Bases. 

1.  POTASSIUM  HYDROXIDE  OR  POTASSA  AND  SODIUM  HYDROXIDE  OR 
SODA  (see  "  Qual.  Anal."). 

All  the  four  sorts  of  the  caustic  alkalies  mentioned  in  the  quali- 
tative part  are  required  in  quantitative  analysis,  viz.,  common  solu- 
tion of  soda,  potassa  purified  with  alcohol,  solution  of  potassa  pre- 
pared with  baryta,  and  absolutely  pure  soda.  Pure  solution  of 
potassa  may  be  obtained  also  by  heating  to  redness  for  half  an  hour 
in  a  copper  crucible,  a  mixture  of  1  part  of  potassium  nitrate,  and 
2  or  3  parts  of  thin  sheet  copper  cut  into  small  pieces,  treating  the 
mass  with  water,  allowing  the  oxide  of  copper  to  subside  in  a  tall 
vessel,  and  removing  the  supernatant  clear  fluid  by  means  of  a 
syphon  (WOHLER).* 

2.  AMMONIA  (see  "  Qual.  Anal."). 

ft.  Alkali-earth  Bases. 

1.  BARIUM  HYDROXIDE  OR  BARYTA  (see  "  Qual.  Anal."). 

2.  CALCIUM  HYDROXDDE  OR  LIME. 

Finely  divided  calcium  hydroxide  mixed  with  water  (milk  of 
lime),  is  used  more  particularly  to  effect  the  separation  of  magne- 
sium, &c.,  from  the  alkali  metals.  Milk  of  lime  intended  to  be 
used  for  that  purpose  must,  of  course,  be  perfectly  free  from  alka- 
lies. To  insure  this  the  slaked  lime  should  be  thoroughly  washed, 
by  repeated  boiling  with  fresh  quantities  of  distilled  water.  This 
operation  is  conducted  best  in  a  silver  dish.  When  cold,  the  milk 
of  lime  so  prepared  is  kept  in  a  well-stoppered  bottle. 

*  Sodium  hydroxide,  made  by  acting  on  pure  water  by  pure  sodium  and  fusing 
in  silver  vessels,  is  to  be  had  cheaply  of  the  Magnesium  Metal  Company,  Salford, 
Manchester,  England. 


110  REAGENTS.  [§  60. 

y.  Heavy  Metals,  and  their  Oxides. 

§  60. 

1.  ZINC. 

Zinc  has  of  late  been  much  used  as  a  reagent  in  quantitative  analy- 
sis. It  serves  more  especially  to  effect  the  reduction  of  ferric  to 
ferrous  salts,  and  also  the  precipitation  of  copper  from  solutions  of 
its  salts.  Zinc  intended  to  be  used  for  the  former  purpose  must  be 
free  from  iron,  for  the  latter  free  from  lead,  copper,  and  other 
metals  which  remain  undissolved  upon  treating  the  zinc  with  dilute 
acids. 

To  procure  zinc  which  leaves  no  residue  upon  solution  in  dilute 
sulphuric  acid,  there  is  commonly  no  other  resource  but  to  re-distil 
the  commercial  article. 

This  is  effected  in  a  retort  made  of  the  material  of  Hessian  or 
black-lead  crucibles.  The  operation  is  conducted  in  a  wind-furnace 
with  good  draught.  The  neck  of  the  retort  must  hang  down  as 
perpendicular  as  possible.  Under  the  neck  is  placed  a  basin  or 
small  tub,  filled  with  water.  The  distillation  begins  as  soon  as  the 
retort  is  at  a  bright  red  heat.  As  the  neck  of  the  retort  is  very 
liable  to  become  choked  up  with  zinc,  or  oxide  of  zinc,  it  is  neces- 
sary to  keep  it  constantly  free  by  means  of  a  pipe-stem.  The  zinc 
obtained  by  this  re-distillation  is  nearly  or  quite  free  from  lead. 

Tests. — The  following  is  the  simplest  way  of  testing  the  purity 
of  zinc :  dissolve  the  metal  in  dilute  sulphuric  acid  in  a  small  flask 
provided  with  a  gas-evolution  tube,  place  the  outer  limb  of  the  tube 
under  water,  and  wThen  the  solution  is  completed,  let  the  water 
entirely  or  partly  recede  into  the  flask ;  after  cooling,  add  to  the 
fluid,  drop  by  drop,  a  sufficiently  dilute  solution  of  potassium  per- 
manganate. If  a  drop  of  that  solution  imparts  the  same  red  tint 
to  the  zinc  solution  as  to  an  equal  volume  of  water,  the  zinc  may  be 
considered  free  from  iron.  I  prefer  this  way  of  testing  the  purity 
of  zinc  to  other  methods,  as  it  affords,  at  the  same  time,  an  ap- 
proximate, or,  if  the  zinc  has  been  weighed,  and  the  permanganate 
solution  (which,  in  that  case,  must  be  considerably  diluted)  measured, 
an  accurate  and  precise  knowledge  of  the  quantity  of  iron  present. 
If  lead  or  copper  are  present,  these  metals  remain  undissolved 
upon  solution  of  the  zinc. 

2.  LEAD  OXIDE. 

Precipitate  pure  lead  nitrate  or  acetate  with  ammonium  car- 


§  61.]  KEAGENTS.  HI 

bonate,  wash  the  precipitate,  dry,  and  ignite  gently  to  complete 
decomposition. 

Lead  oxide  is  often  used  to  fix  an  acid,  so  that  it  is  not  expelled 
even  by  a  red  heat. 

b.  Sulphur  Bases. 

1.  AMMONIUM  SULPHIDE  (see  "  Qual.  Anal."). 

We  require  both  the  colorless  monosulphide,  and  the  yellow 
polysulphide. 

2.  SODIUM  SULPHIDE  (sep  "  Qual.  Anal."). 

IV.   SALTS. 

a.  Salts  of  the  Alkalies. 
§  61. 

1.  POTASSIUM  SULPHATE  (see  "  Qual.  Anal."). 

2.  AMMONIUM  OXALATE  (see  "  Qual.  Anal."). 

3.  SODIUM  ACETATE  (see  "  Qual.  Anal."). 

4.  AMMONIUM  SUCCTNATE. 

Preparation. — Saturate  succinic  acid,  which  has  been  purified 
by  dissolving  in  nitric  acid  and  recrystallizing,  with  dilute  ammo- 
nia. The  reaction  of  the  new  compound  should  be  rather  slightly 
alkaline  than  acid. 

Uses. — This  reagent  serves  occasionally  to  separate  ferric  iron 
from  other  metals. 

5.  SODIUM  CARBONATE  (see  "  Qual.  Anal."). 

This  reagent  is  required  both  in  solution  and  in  pure  crystals ; 
in  the  latter  form  to  neutralize  an  excess  of  acid  in  a  fluid  which 
it  is  desirable  not  to  dilute  too  much. 

6.  AMMONIUM  CARBONATE  (see  "Qual.  Anal."). 

7.  SODIUM  HYDROGEN  SULPHITE  (see  "  Qual.  Anal."). 

8.  SODIUM  THIOSULPHATE  (HYPOSULPHITE),  N2S2O3. 

This  salt  occurs  in  commerce.  It  should  be  dry.  clear,  well 
crystallized,  completely  and  with  ease  soluble  in  water.  The  solu- 
tion must  give  with  silver  nitrate  at  first  a  white  precipitate,  must 
not  effervesce  with  acetic  acid,  and  when  acidified  must  give  no  pre- 
cipitate with  barium  chloride,  or  at  most,  only  a  slight  turbidity. 
The  acidified  solution  must,  after  a  short  time,  become  milky  from 
separation  of  sulphur. 


EEAGENTS.  [§  62. 

Uses.  —  Sodium  thiosulphate  is  used  for  the  precipitation  of 
several  metals,  as  sulphides,  particularly  in  separations,  for  instance, 
of  copper  from  zinc  ;  it  also  serves  as  solvent  for  several  salts  (sil- 
ver chloride,  calcium  sulphate,  &c.)  ;  lastly,  it  is  employed  in  volu- 
metric analysis,  its  use  here  depending  on  the  reaction  2(Na2SaO3) 


9.  POTASSIUM  NITRITE  (see  "  Qual.  Anal."). 

10.  POTASSIUM  DICHROMATE  (see  "  Qual.  Anal."). 

11.  AMMONIUM  MOLYBDATE  (see  "  Qual.  Anal."). 

12.  AMMONIUM  CHLORIDE  (see  "Qual.  Anal."). 

13.  POTASSIUM  CYANIDE  (see  "  Qual.  Anal."). 

b.  Salts  of  the  Alkali-earth  Metals. 
§  62. 

1.  BARIUM  CHLORIDE  (see  "  Qual.  Anal."). 

The  following  process  gives  a  very  pure  barium  chloride,  free 
from  calcium  and  strontium  :  —  Transmit  through  a  concentrated 
solution  of  impure  barium  chloride  hydrochloric  gas,  as  long  as  a 
precipitate  continues  to  form.  Nearly  the  whole  of  the  barium 
chloride  present  is  by  this  means  separated  from  the  solution,  in 
form  of  a  crystalline  powder.  Collect  this  on  a  filter,  let  the 
adhering  liquid  drain  off,  wash  the  powder  repeatedly  with  small 
quantities  of  pure  hydrochloric  acid,  until  a  sample  of  the  wash- 
ings, diluted  with  water,  and  precipitated  with  sulphuric  acid, 
gives  a  filtrate  which,  upon  evaporation  in  a  platinum  dish,  leaves 
no  residue.  The  hydrochloric  mother-liquor  serves  to  dissolve 
fresh  portions  of  witherite.  I  make  use  of  the  barium  chloride  so 
obtained,  principally  for  the  preparation  of  perfectly  pure  barium 
carbonate,  which  is  often  required  in  quantitative  analyses. 

2.  BARIUM  ACETATE. 

Preparation.  —  Dissolve  pure  barium  carbonate  in  moderately 
dilute  acetic  acid,  filter,  and  evaporate  to  crystallization. 

Tests.  —  Dilute  solution  of  barium  acetate  must  not  be  rendered 
turbid  by  solution  of  silver  nitrate.  See  also  "  Qual.  Anal.,"  Barium 
chloride,  the  same  tests  being  also  used  to  ascertain  the  purity  of 
the  acetate. 

Uses.  —  Barium  acetate  is  used  instead  of  barium  chloride,  to 
effect  the  precipitation  of  sulphuric  acid,  in  cases  where  it  is  desir- 


§  63.]  REAGENTS.  113 

able  to  avoid  the  introduction  of  a  chloride  into  the  solution,  or 
to  convert  the  base  into  an  acetate.  As  the  reagent  is  seldom 
required,  it  is  best  kept  in  crystals. 

3.  BARIUM  CARBONATE  (see  "Qual.  Anal."). 

4.  STRONTIUM  CHLORIDE. 

Preparation. — Strontium  chloride  is  prepared  from  strontian- 
ite  or  celestine,  by  the  same  processes  as  barium  chloride.  The 
pure  crystals  obtained  are  dissolved  in  alcohol  of  96  per  cent.,  the 
solution  is  filtered,  and  kept  for  use. 

Uses. — The  alcoholic  solution  of  strontium  chloride  is  used  to 
effect  the  conversion  of  alkali  sulphates  into  chlorides,  in  cases 
where  it  is  desirable  to  avoid  the  introduction  into  the  fluid  of  a 
salt  insoluble  in  alcohol. 

5.  CALCIUM  CHLORIDE  (see  "  Qual.  Anal."). 

6.  MAGNESIUM  CHLORIDE  OR  MAGNESIUM  MIXTURE. 
Dissolve  11  parts  crystallized  magnesium  chloride  (MgCl,  +  6 

H3O)  and  28  parts  ammonium  chloride  in  130  parts  water,  add 
70  parts  dilute  ammonia  solution  (sp.  gr.  0'96).  Allow  the  mix- 
ture to  stand  one  or  two  days  and  filter.  This  solution,  commonly 
called  "  magnesia  mixture,"  is  used  to  precipitate  phosphoric  acid. 
An  excess  is  required  to  effect  complete  precipitation.  Prepared 
as  here  described,  about  10  c.  c.  should  be  used  in  ordinary  cases 
for  every  O'l  gramme  P,O5. 

A  solution  containing  the  same  per  cent,  (approximately)  of 
magnesium  chloride  and  other  constituents  may  also  be  prepared 
from  common  calcined  magnesia  (MgO),  provided  it  is  free  from 
the  other  alkali-earth  metals,  as  follows : — Add  to  11  parts  magnesia 
sufficient  hydrochloric  acid  to  effect  solution,  next  add  a  slight  ex- 
cess of  magnesia  and  boil  to  separate  traces  of  iron ;  filter,  and  add 
140  parts  ammonium  chloride  and  350  parts  dilute  ammonia. 
Dilute  with  water  until  volume  equals  1000  c.  c.  for  every  11 
grammes  of  MgO  used.  Allow  the  mixture  to  stand  two  or  three 
days,  and  filter  if  necessary. 

c.  Salts  of  the  Heavy  Metals. 
§  63. 

1.  FERROUS  SULPHATE  (see  "Qual.  Anal."). 

2.  FERRIC  CHLORIDE  (see  "  Qual.  Anal."). 

3.  URANIC  ACETATE. 


114  REAGENTS.  [§  64. 

Heat  finely  powdered  pitchblende  with  dilute  nitric  acid,  filter 
the  fluid  from  the  undissolved  portion,  and  treat  the  filtrate  with 
hydrosulphuric  acid  to  remove  the  lead,  copper,  and  arsenic;  filter 
again,  evaporate  to  dryness,  extract  the  residue  with  water,  and  fil- 
ter the  solution  from  the  oxides  of  iron,  cobalt,  and  manganese. 
Uranic  nitrate  crystallizes  from  the  filtrate ;  purify  this  by  recrys- 
tallization,  and  then  heat  the  crystals  until  a  small  portion  of  uranic 
oxide  is  reduced.  Warm  the  yellowish-red  mass  thus  obtained 
with  acetic  acid,  filter  and  let  the  filtrate  crystallize.  The  crystals 
are  uranic  acetate,  and  the  mother-liquor  contains  the  undecom- 
posed  nitrate  (WERTHEIM). 

Tests. — Solution  of  uranic  acetate  after  acidification  with 
hydrochloric  acid  must  not  be  altered  by  hydrosulphuric  acid; 
ammonium  carbonate  must  produce  in  it  a  precipitate,  soluble  in  an 
excess  of  the  precipitant. 

Use-s. — Uranic  acetate  may  serve,  in  many  cases,  to  effect  the 
separation  and  determination  of  phosphoric  acid. 

4.  SILVER  NITRATE  (see  "  Qual.  Anal."). 

5.  LEAD  ACETATE  (see  "  Qual.  Anal."). 

6.  MERCURIC  CHLORIDE  (see  "  Qual.  Anal."). 

7.  STANNOUS  CHLORIDE  (see  "  Qual.  Anal."). 

8.  PLATINIC  CHLORIDE  (see  "  Qual.  Anal."). 

9.  SODIUM  PALLADIO-CHLORIDE  (see  "  Qual.  Anal."). 


B.    REAGENTS  FOR  GRA  VIMETRIC  ANAL  YSIS  IN  THE  DR  Y  WA  Y. 

§  64. 

1.  SODIUM  CARBONATE,  pure  anhydrous  (see  "  Qual.  Anal."). 

2.  MIXED  SODIUM  AND  POTASSIUM  CARBONATES  (see  "  Qual. 
Anal."). 

3.  BARIUM  HYDROXIDE  OR  BARYTA  (see  "  Qual.  Anal."  and 
§59). 

4.  POTASSIUM  NITRATE  (see  "  Qual.  Anal."). 

5.  SODIUM  NITRATE  (see  "  Qual.  Anal."). 
G.  BORAX  (fused). 

Preparation. — Heat  crystallized  borax  (see  "  Qual.  Anal.)  in  a 
platinum  or  porcelain  dish,  until  there  is  no  further  intumescence; 
reduce  the  porous  mass  to  powder,  and  heat  this  in  a  platinum  cru- 
cible until  it  is  fused  to  a  transparent  mass.  Pour  the  semi-fluid, 


§  64.]  EEAGENTS.  115 

viscid  mass  upon  a  fragment  of  porcelain.  A  better  way  is  to  fuse 
the  borax  in  a  net  of  platinum  gauze,  bj  making  the  gas  blowpipe- 
flame  act  upon  it.  The  drops  are  collected  in  a  platinum  dish. 
The  vitrified  borax  obtained  is  kept  in  a  well-stoppered  bottle. 
But  as  it  is  always  necessary  to  heat  the  vitrified  borax  previous  to 
use,  to  make  quite  sure  that  it  is  perfectly  anhydrous,  the  best  way 
is  to  prepare  it  only  when  required. 

Uses. — Vitrified  borax  is  used  to  effect  the  expulsion  of  car- 
bonic acid  and  other  volatile  acids,  at  a  red  heat. 

7.  POTASSIUM  DISULPHATE. 

Preparation. — Mix  87  parts  of  normal  potassium  sulphate  (see 
"  Qual.  Anal."),  in  a  platinum' crucible,  with  49  parts  of  concen- 
trated pure  sulphuric  acid,  and  heat  to  gentle  redness  until  the  mass 
is  in  a  state  of  uniform  and  limpid  fusion.  Pour  the  fused  salt  on 
a  fragment  of  porcelain,  or  into  a  platinum  dish  standing  in  cold 
water.  After  cooling,  break  the  mass  into  pieces,  and  keep  for 
use.* 

Uses. — This  reagent  serves  as  a  flux  for  certain  native  com- 
pounds of  alumina  and  chromic  oxide.  Potassium  disulphate  is 
used  also,  as  we  have  already  had  occasion  to  state,  for  the  cleansing 
of  platinum  crucibles;  for  this  latter  purpose,  however,  the  salt 
which  is  obtained  in  the  preparation  of  nitric  acid  will  be  found 
sufficiently  pure. 

8.  AMMONIUM  CARBONATE  (solid). 

Preparation. — See  "  Qual.  Anal." — This  reagent  serves  to  con- 
vert the  acid  alkali  sulphates  into  normal  salts.  It  must  com- 
pletely volatilize  when  heated  in  a  platinum  dish. 

9.  AMMONIUM  TITRATE. 

Preparation. — Neutralize  pure  ammonium  carbonate  with  pure 
nitric  acid,  warm,  and  add  ammonia  to  slightly  alkaline  reaction ; 
filter,  if  necessary,  and  let  the  filtrate  crystallize.  Fuse  the  crys- 
tals in  a  platinum  dish,  and  pour  the  fused  mass  upon  a  piece  of 
porcelain ;  break  into  pieces  whilst  still  warm,  and  keep  in  a  well- 
stoppered  bottle. 

Tests. — Ammonium  nitrate  must  leave  no  residue  when  heated 
in  a  platinum  dish. 

*  [J.  Lawrence  Smith  advises  the  use  of  sodium  disulphate  for  fluxing  alumi- 
nous compounds,  as  the  fused  mass  is  much  more  readily  soluble  in  water.] 


116  REAGENTS.  [§  64. 

Uses. — Ammonium  nitrate  serves  as  an  oxidizing  agent ;  for 
instance,  to  convert  lead  into  lead  oxide,  or  to  effect  the  com- 
bustion of  carbon,  in  cases  where  it  is  desired  to  avoid  the  use  of 
iixed  salts- 

10.  AMMONIUM  CHLORIDE. 
Preparation  and  Tests. — See  "  Qual.  Anal." 

Uses. — Ammonium  chloride  is  often  used  to  convert  metallic 
oxides  and  acids,  e.g.,  lead  oxide,  zinc  oxide,  stannic  oxide,  arsenic 
acid,  antimonic  acid,  &c.,  into  chlorides  (ammonia  and  water  escape 
in  the  process).  Many  metallic  chlorides  being  volatile,  and  others 
volatilizing  in  presence  of  ammonium  chloride  fumes,  they  may  be 
completely  removed  by  igniting  them  with  ammonium  chloride  in 
excess,  and  thus  many  compounds,  e.g.,  alkali  antimonates,  may 
be  easily  and  expeditiously  analyzed.  Ammonium  chloride  is 
also  used  to  convert  various  salts  of  other  acids  into  chlorides,  e.g., 
small  quantities  of  alkali  sulphates. 

11.  HYDROGEN  GAS. 

Preparation. — Hydrogen  gas  is  evolved  when  dilute  sulphuric 
acid  is  added  to  granulated  zinc.  It  may  be  purified  from  traces 
of  foreign  gases  either  by  passing  first  through  mercuric  chloride 
solution,  then  through  potash  solution,  or  as  recommended  by 
STENHOUSE,  by  passing  through  a  tube  filled  with  pieces  of  char- 
coal. If  the  gas  is  desired  dry,  pass  through  sulphuric  acid  or  a 
calcium  chloride  tube. 

Tests. — Pure  hydrogen  gas  is  inodorous.  It  ought  to  burn  with 
a  colorless  flame,  which,  when  cooled  by  depressing  a  porcelain 
dish  upon  it,  must  deposit  nothing  on  the  surface  of  the  dish  except 
pure  water  (free  from  acid  reaction). 

Uses. — Hydrogen  gas  is  frequently  used,  in  quantitative  analy- 
sis, to  reduce  oxides,  chlorides,  sulphides,  &c.,  to  the  metallic  state. 

12.  CHLORINE. 

Preparation. — See  "  Qual.  Anal." — Chlorine  gas  is  purified  and 
dried  by  transmitting  it  through  concentrated  sulphuric  acid,  or  a 
calcium  chloride  tube. 

Uses. — Chlorine  gas  serves  principally  to  produce  chlorides, 
and  to  separate  the  volatile  from  the  non-volatile  chlorides;  it  is 
also  used  to  displace  and  indirectly  determine  bromine  and  iodine. 


§  65.]  KEAGENTS.  11? 

G.   REAGENTS   USED  IN  VOLUMETRIC  ANALYSIS. 

§65. 

Under  this  head  are  arranged  the  most  important  of  those 
substances,  which  serve  for  the  preparation  and  testing  of  the 
fluids  required  in  volumetric  analysis,  and  have  not  been  given 
sub  A  and  B. 

1.  PUKE  CRYSTALLIZED  OXALIC  ACID,  HaC3O4  -f-  2HaO. 
The  introduction  of  crystallized  oxalic  acid  as  a  basis  for  alkali- 
metry and  acidiraetry  is  due  to  FR.  MOHR.     It  is  also  employed  to 
determine  the  strength  of,  or  to  standardize,  a  solution  of  potas- 
sium permanganate,  1  molecule  of  potassium  permanganate  being 
required,  in  the  presence  of  free  sulphuric  acid,  to  convert  5  mole 
cules  of  oxalic  acid  into  carbon  dioxide  and  water  (KaMnaO8  -(- 
5HaCa04  +  3HaS04  =  KaS04  +  2MnSO4  +  8H2O  +  lOCO,). 
We  use  in  most  cases  the  pure  crystallized  acid  which  has  the 
formula  HaC2O4  -j-  2HaO,  and  of  which  the  molecular  weight  is 
accordingly  126. 

Preparation. — See  "  Qual.  Anal.,"  under  Ammonium  Oxalate. 

Tests. — The  crystals  of  oxalic  acid  must  not  show  the  least  sign 
of  efflorescence  (to  which  they  are  liable  even  at  20°  in  a  dry 
atmosphere) ;  they  must  dissolve  in  water  to  a  perfectly  clear  fluid ; 
when  heated  in  a  platinum  dish,  they  must  leave  no  fixed  and 
incombustible  residue  (calcium  carbonate,  potassium  carbonate, 
&c.).  If  the  acid  obtained  by  a  first  crystallization  fails  to  satisfy 
these  requirements,  it  must  be  recrystallized. 

2.  TINCTURE  OF  LITMUS. 

Preparation. — Digest  1  part  of  litmus  of  commerce  with  6 
parts  of  water,  on  the  water-bath,  for  some  time,  filter,  divide  the 
blue  fluid  into  2  portions,  and  saturate  in  one  half  the  free  alkali, 
by  stirring  repeatedly  with  a  glass  rod  dipped  in  very  dilute  nitric 
acid,  until  the  color  just  appears  red ;  add  the  remaining  blue  half, 
together  with  1  part  of  strong  spirit  of  wine,  and  'keep  the  tincture 
which  is  now  ready  for  use,  in  a  small  open  bottle,  not  quite  full, 
in  a  place  protected  from  dust.  In  a  stoppered  bottle  the  tincture 
would  speedily  lose  color. 

Tests. — Litmus  tincture  is  tested  by  coloring  with  about  100 
cubic  centimetres  of  water  distinctly  blue,  dividing  the  fluid  into 


118  KEAGENTS.  [§  65. 

two  portions,  and  adding  to  the  one  the  least  quantity  of  a  dilute 
acid,  to  the  other  a  trace  of  solution  of  soda.  If  the  one  portion 
acquires  a  distinct  red,  the  other  a  distinct  blue  tint,  the  litmus 
tincture  is  fit  for  use,  as  neither  acid  nor  alkali  predominates. 

3.  POTASSIUM  PERMANGANATE. 

Preparation. — Mix  8  parts  of  very  finely  powdered  pure  pyro- 
lusite,  or  manganese  binoxide,  with  7  parts  of  potassium  chlorate, 
put  the  mixture  into  a  shallow  cast-iron  pot,  and  add  37  parts  of  a 
solution  of  potassa  of  1*27  specific  gravity  (the  same  solution  as 
is  used  in  organic  analysis  *) ;  evaporate  to  dry  ness,  stirring  the 
mixture  during  the  operation ;  put  the  residue  before  it  has  ab- 
sorbed moisture,  into  an  iron  or  Hessian  crucible,  and  expose  to  a 
dull-red  heat,  with  frequent  stirring  with  an  iron  rod  or  iron  spa- 
tula, until  no  more  aqueous  vapors  escape  and  the  mass  is  in  a  faint 
glow.  Remove  the  crucible  now  from  the  fire,  and  transfer  the 
friable  mass  to  an  iron  pot.  Reduce  to  coarse  powder,  and  transfer 
this,  in  small  portions  at  a  time,  to  an  iron  vessel  containing  100 
parts  of  boiling  water;  keep  boiling,  replacing  the  evaporating 
water,  and  passing  a  stream  of  carbon  dioxide  through  the  fluid 
(  MULDER  f).  The  originally  dark-green  solution  of  potassium 
manganate  soon  changes,  with  separation  of  hydrated  manganese 
binoxide,  to  the  deep  violet-red  of  the  permanganate.  When  it  is 
considered  that  the  conversion  is  complete,  allow  to  settle,  take 
out  a  small  quantity  of  the  clear  liquid,  boil  and  pass  carbon 
dioxide  through  it.  If  a  precipitate  forms,  the  conversion  is  not 
yet  complete. 

The  solution  may  be  filtered  through  gun-cotton.  Evaporate, 
crystallize,  and  dry  the  crystals  on  a  porous  tile. 

The  pure  salt  is  now  to  be  obtained  in  commerce. 

4.  AMMONIUM  FERROUS  SULPHATE. 

FeS04.(KE4)2S04  +  6H3O. 

FR.  MOHR  has  proposed  to  employ  this  double  salt,  which  is  not 
liable  to  efflorescence  and  oxidation,  as  an  agent  to  determine  the 
strength  of  the  permanganate  solution. 

Preparation. — Take  two  equal  portions  of  dilute   sulphuric 

*  Or  instead  of  the  solution,  use  10  parts  of  the  hydroxide  KOH.  In  this  case 
fuse  the  potash  and  the  chlorate  together  first;  and  then  project  the  manganese 
into  the  crucible. 

f  Jahresbericht  von  Kopp  und  Will,  1858,  581. 


§  65.]  REAGENTS.  119 

acid,  and  warm  the  one  with  a  moderate  excess  of  small  iron 
nails  free  from  rust,  until  the  evolution  of  hydrogen  gas  has  alto- 
gether or  very  nearly  ceased  ;  neutralize  the  other  portion  exactly 
with  ammonium  carbonate,  and  then  add  to  it  a  few  drops  of  dilute 
sulphuric  acid.  Filter  the  solution  of  the  ferrous  sulphate  into  that 
of  the  ammonium  sulphate,  evaporate  the  mixture  a  little,  if  neces- 
sary, and  then  allow  the  salt  to  crystallize.  Let  the  crystals,  which 
are  hard  and  of  a  pale-green  color,  drain  in  a  funnel,  then  wash 
them  in  a  little  water,  dry  thoroughly  on  blotting-paper  in  the  air, 
and  keep  for  use. 

The  molecular  weight  of  the  salt  (392)  is  exactly  7  times  the 
atomic  weight  of  iron  (56).  The  solution  of  the  salt  in  water 
which  has  been  just  acidified  with  sulphuric  acid  must  not  become 
red  on  the  addition  of  potassium  sulphocyanate. 

5.  AMMONIA-IKON-ALUM. 


Preparation.  —  Bring  into  a  large  porcelain  dish  58  grms.  of 
pure  crystallized  ferrous  sulphate  (see  Fresenius'  "Qual.  Anal." 
Am.  ed.,  p.  73),  together  with  a  quantity  of  oil  of  vitriol  equiva- 
lent to  8-3  grms.  of  sulphuric  anhydride  (SO8),  (see  Table,  §  1(J1). 
Heat  upon  a  sand-bath,  adding  nitric  acid  from  time  to  time,  in 
small  portions,  until  the  iron  has  all  passed  into  ferric  sulphate,  or 
until  a  drop  of  the  solution  gives  no  blue  coloration  with  potassium 
ferricyanide.  Heat  further,  and  evaporate  until  the  excess  of 
nitric  acid  is  expelled,  then  add  14  grms.  of  ammonium  sulphate,* 
and,  if  need  be,  hot  water  sufficient  to  bring  the  salt  into  solution  ; 
filter  into  a  porcelain  capsule  and  set  aside,  under  cover,  to  crys- 
tallize. 

The  iron-alum  separates  in  cubo-octahedrons,  which  may  be  yel- 
lowish, lilac,  or  colorless.  If  dark  in  color,  dissolve  in  warm  water, 
add  a  few  drops  of  oil  of  vitriol,  and  crystallize  again.  Rinse  the 
pale  or  colorless  crystals,  after  separation  from  the  mother-liquor, 
with  cold  water,  wrap  up  closely  in  filter  paper,  and  allow  them  to 
dry  at  the  ordinary  temperature.f 

*  If  not  on  hand,  this  salt  may  be  prepared  by  saturating  oil  of  vitriol  with 
ammonium  carbonate  and  evaporating  to  dryness.  30  grammes  of  oil  of  vitriol 
give  somewhat  more  than  is  required  above. 

f  Examinations  of  iron-alum  thus  prepared  show  that  the  variations  in  the 


120  REAGENTS.  [§  65. 

The  yield  should  be  about  80  grms.  The  dry  salt  should 
be  pulverized,  pressed  between  folds  of  paper  until  freed  from 
mechanically  adhering  water,  and  preserved  in  a  well-stoppered 
bottle. 

Uses.  —  Ammonia-iron-alum  furnishes  the  best  means  of  obtain- 
ing a  definite  quantity  of  iron  in  a  ferric  salt  for  making  standard 
solutions,  being  easily  obtained  pure  and  inalterable  if  kept 
away  from  acid  vapors.  Its  purity  may  be  readily  controlled  by 
ascertaining  the  loss  on  careful  ignition,  which  should  leave  a  resi- 
due of  16*6  per  cent,  of  ferric  oxide  of  iron,  corresponding  to  11*62 
per  cent,  of  metallic  iron. 

6.  PUKE  IODINE. 

Preparation.  —  Triturate  iodine  of  commerce  with  -J  part  of  its- 
weight  of  potassium  iodide,  dry  the  mass  in  a  large  watch-glass  with 
ground  rim,  warm  this  gently  on  a  sand-bath,  or  on  an  iron  plate, 
and  as  soon  as  violet  fumes  begin  to  escape,  cover  it  with  another 
watch-glass  of  the  same  size.  Continue  the  application  of  heat 
until  all  the  iodine  is  sublimed,  and  keep  in  a  well-closed  glass 
bottle.  The  chlorine  or  bromine,  which  is  often  found  in  iodine 
of  commerce,  combines,  in  this  process,  with  the  potassium,  and 
remains  in  the  lower  watch-glass,  together  with  the  excess  of 
potassium  iodide. 

Tests.  —  Iodine  purified  by  the  process  just  now  described,  must 
leave  no  fixed  residue  when  heated  on  a  watch-glass.  But,  even 
supposing  it  should  leave  a  trace  on  the  glass,  it  would  be  of  no 
great  consequence,  as  the  small  portion  intended  for  use  has  to  be 
resublimed  immediately  before  weighing. 

color  of  the  salt,  from  colorless  to  rose,  are  not  connected  with  appreciable 
differences  of  composition. 

J.  H.  Grove,  of  the  Sheffield  Laboratory,  obtained  the  following  results  in  the 
examination  of  ammonia-iron-alum  crystals,  the  ferric  oxide  being  estimated  by 
ignition  :  — 

Fe203 
(      16-59 

1st  \      16-55 

(      16-59 

2d  16-53 

3d  16-57 

4th  16-57 

5th  16-58 


fith          J 

6tn          \  16-56 

7th  16-55 

Calculated  16'60 


§  65.]  REAGENTS. 

Uses. — Pure  iodine  is  used  to  determine  the  amount  of  iodine 
contained  in  the  solution  of  iodine  in  potassium  iodide,  employed 
in  many  volumetric  processes. 

7.  POTASSIUM  IODIDE. 

Small  quantities  of  this  article  may  be  procured  cheaper  in 
commerce  than  prepared  in  the  laboratory.  For  the  preparation  of 
potassium  iodide  intended  for  analytical  purposes  I  recommend 
BAUP'S  method,  improved  by  FREDERKING,  because  the  product 
obtained  by  this  process  is  free  from  iodic  acid. 

Tests. — Put  a  sample  of  the  salt  in  dilute  sulphuric  acid.  If 
the  iodide  is  pure,  it  will  dissolve  without  coloring  the  fluid ;  but 
if  it  contain  potassium  iodate,  the  fluid  will  acquire  a  brown  tint, 
from  the  presence  of  free  iodine,  the  sulphuric  acid  setting  free  iodic 
and  hydriodic  acids  which  react  on  each  other  (HIO3  -f-  (HI)5  = 
(H2O)3  -f-  I6)  with  liberation  of  iodine  which  remains  in  solution. 
Mix  the  solution  of  another  sample  with  silver  nitrate,  as  long  as 
a  precipitate  continues  to  form  ;  add  solution  of  ammonia  in  excess, 
shake  the  mixture,  filter,  and  supersaturate  the  filtrate  with  nitric 
acid.  The  formation  of  a  white,  curdy  precipitate  indicates  the 
presence  of  chloride  in  the  potassium  iodide.  Presence  of  potassium 
sulphate  is  detected  by  means  of  solution  of  barium  chloride, 
with  addition  of  some  hydrochloric  acid. 

Uses. — Potassium  iodide  is  used  as  a  solvent  for  iodine  in  the 
preparation  of  standard  solutions  of  iodine ;  it  is  employed  also  to 
absorb  free  chlorine.  In  the  latter  case  every  atom  of  chlorine  lib- 
erates an  atom  of  iodine,  which  is  retained  in  solution  by  the  agency 
of  the  excess  of  potassium  iodide.  The  potassium  iodide  intended 
for  these  uses  must  be  free  from  potassium  iodate  and  carbonate; 
the  presence  of  trifling  traces  of  potassium  chloride  or  potassium 
sulphate  is  of  no  consequence.  • 

8.  ARSENIOUS  OXIDE  (As3O3). 

The  arsenious  oxide  sold  in  the  shops  in  large  pieces,  externally 
opaque,  but  often  still  vitreous  within,  is  generally  quite  pure. 
The  purity  of  the  article  is  tested  by  moderately  heating  it  in  a 
glass  tube,  open  at  both  ends,  through  which  a  feeble  current  of 
air  is  transmitted.  Pure  arsenious  oxide  must  completely  volatilize 
in  this  process  ;  no  residue  must  be  left  in  the  tube  upon  the 
expulsion  of  the  sublimate  from  it.  If  a  non-volatile  residue  is  left 
which,  when  heated  in  a  current  of  hydrogen  gas,  turns  black,  the 


122  EEAGENTS.  [§  65. 

arsenious  oxide  contains  antimony  teroxicle,  and  is  unfit  for  use  in 
analytical  processes.  Dissolve  about  10  grms.  of  the  arsenious 
oxide  to  be  tested  in  soda,  and  add  1 — 2  drops  lead  acetate.  If  a 
brownish  color  is  produced,  the  arsenious  oxide  contains  arsenious 
sulphide  and  cannot  be  used.  Arsenious  oxide  dissolves  in  a 
solution  of  sodium  carbonate  forming  sodium  arsenite  which  is 
used  to  determine  hypochlorous  acid,  free  chlorine,  iodine,  &c. 

9.  SODIUM  CIILOKIDE. 

Perfectly  pure  rock-salt  is  best  suited  for  analytical  purposes. 
It  must  dissolve  in  water  to  a  clear  fluid ;  ammonium  oxalate,  sodium 
phosphate,  and  barium  chloride  must  not  trouble  the  solution. 
Pure  sodium  chloride  may  be  prepared  also  by  MAKGUERITTE'S 
process,  viz.,  conduct  into  a  concentrated  solution  of  common  salt 
hydrochloric  gas  to  saturation,  collect  the  small  crystals  of  sodium 
chloride  which  separate  on  a  funnel,  let  them  thoroughly  drain, 
wash  with  hydrochloric  acid,  and  dry  the  sodium  chloride  finally 
in  a  porcelain  dish,  until  the  hydrochloric  acid  adhering  to  it  has 
completely  evaporated.  The  mother-liquor  contains  the  small 
quantities  of  calcium  sulphate,  magnesium  chloride,  &c.,  originally 
present  in  the  salt. 

Uses. — Sodium  chloride  serves  as  a  volumetric  precipitating 
agent  in  the  determination  of  silver,  and  also  to  determine  the 
strength  of  solutions  of  silver  intended  for  the  estimation  of  chlo- 
rine. We  usually  fuse  it  before  weighing.  The  operation  must 
be  conducted  with  caution,  and  must  not  be  continued  longer  than 
necessary  ;  for  if  the  gas-flame  acts  on  the  salt,  hydrochloric  acid 
escapes,  -while  sodium  carbonate  is  formed. 

10.  METALLIC  SHAVER. 

The  silver  obtained  by  the  proper  reduction  of  the  pure  chlo- 
ride of  the  metal  alone  can  be  called  chemically  pure.  The  silver 
precipitated  by  copper  is  never  absolutely  pure,  but  contains  gener- 
ally about  yoVjj  °f  copper. 

Chemically  pure  silver  is  only  used  in  small  quantity  to  prepare 
the  dilute  solution  employed  for  the  determination  of  silver.  The 
solution  of  silver  required  for  the  estimation  of  chlorine  need  not 
be  made  with  absolutely  pure  silver,  as  the  strength  of  this  solu- 
tion had  always  best  be  determined  after  the  preparation,  by  means 
of  pure  sodium  chloride. 


§  66.]  REAGENTS.         ,  123 

D.    REAGENTS  USED  IN  ORGANIC  ANALYSIS. 

§  66.- 
1.'  CUPRIC  OXIDE. 

Preparation. — Stir  pure*  copper  scales  (which  should  first  be 
ignited  in  a  muffle)  with  pure  nitric  acid  in  a  porcelain  dish  to  a 
thick  paste  ;  after  the  effervescence  has  ceased,  heat  gently  on  the 
sand-bath  until  the  mass  is  perfectly  dry.  Transfer  the  green  basic 
salt  produced  to  a  Hessian  crucible,  and  heat  to  a  moderate  redness, 
until  no  more  fumes  of  hyponitric  acid  escape  ;  this  may  be  known 
by  the  smell,  or  by  introducing  a  small  portion  of  the  mass  into  a 
test  tube,  closing  the  latter  with  the  finger,  heating  to  redness,  and 
then  looking  through  the  tube  lengthways.  The  uniform  decom- 
position of  the  salt  in  the  crucible  may  be  promoted  by  stirring 
the  mass  from  time  to  time  with  a  hot  glass  rod.  When  the  cruci- 
ble has  cooled  a  little,  reduce  the  mass,  which  now  consists  of  pure 
cupric  oxide,  to  a  tolerably  fine  powder,  by  triturating  it  in  a  brass 
or  porcelain  mortar ;  pass  through  a  metal  sieve,  and  keep  in  a 
well-stoppered  bottle  for  use.  It  is  always  advisable  to  leave  a 
small  portion  of  the  oxide  in  the  crucible,  and  to  expose  this  again 
to  an  intense  red  heat.  This  agglutinated  portion  is  not  pounded, 
but  simply  broken  into  small  fragments. 

Another  method  is  to  dissolve  pure  copper  in  pure  nitric  acid, 
evaporate  to  dryness  in  a  porcelain  dish,  ignite  the  copper  nitrate 
thus  obtained  in  a  Hessian  crucible  until  no  fumes  arise  on  stirring 
the  top  of  the  mass  with  a  rod.  A  portion  in  the  bottom  of  the 
crucible  will  be  sintered  if  a  proper  heat  has  been  applied,  while 
the  upper  part  will  be  pulverulent.  Treat  the  sintered  portion  as 
above,  and  reserve  each  separately.  This  method  gives  a  reliable 
product.  . 

Tests. — Pure  cupric  oxide  is  a  compact,  heavy,  deep-black  pow- 
der, gritty  to  the  touch  ;  upon  exposure  to  a  red  heat  it  must  evolve 
no  hyponitric  acid  fumes,  nor  carbon  dioxide ;  the  latter  would 
indicate  presence  of  fragments  of  charcoal,  or  particles  of  dust.  It 
must  contain  nothing  soluble  in  water.  That  portion  of  the  oxide 
which  has  been  exposed  to  an  intense  red  heat  should  be  hard, 
and  of  a  grayish-black  color. 

*  If  the  scales  contain  lime,  digest  them  with  water,  containing  a  little  nitric 
acid,  for  a  long  time,  wash,  and  then  proceed  as  above. 


124  REAGENTS.  [§  00. 

Uses. — Cupric  oxide  serves  to  oxidize  the  carbon  and  hydrogen 
of  organic  substances,  yielding  up  its  oxygen  wholly  or  in  part, 
according  to  circumstances.  That  portion  of  the  oxide  which  has 
been  heated  to  the  most  intense  redness  is  particularly  useful  in  the 
analysis  of  volatile  fluids. 

JST.B.  The  cupric  oxide,  after  use,  may  be  regenerated  by  oxi- 
dation with  nitric  acid,  and  subsequent  ignition.  Should  it  have 
become  mixed  with  alkali  salts  in  the  course  of  the  analytical  pro- 
cess, it  is  first  digested  with  very  dilute  cold  nitric  acid,  and  washed 
afterwards  with  water.  To  purify  cupric  oxide  containing  chlo- 
ride, E.  EKLENMEYER  recommends  to  ignite  it  in  a  tube,  first  in  a 
stream  of  moist  air,  and  finally,  when  the  escaping  gas  ceases  to 
redden  litmus  paper,  in  dry  air.  By  these  operations  any  oxides 
of  nitrogen  that  may  have  remained  are  also  removed. 

2.  LEAD  CHROMATE. 

Preparation. — Precipitate  a  clear  filtered  solution  of  lead  ace- 
tate, slightly  acidulated  with  acetic  acid,  with  a  small  excess  of 
potassium  dichromate  ;  wash  the  precipitate  by  decantation,  and  at 
last  on  a  linen  strainer ;  dry,  put  in  a  Hessian  crucible,  and  heat  to 
bright  redness  until  the  mass  is  fairly  in  fusion.  Pour  out  upon  a 
stone  slab  or  iron  plate,  break,  pulverize,  pass  through  a  fine 
metallic  sieve,  and  keep  the  tolerably  fine  powder  for  use. 

Tests. — Lead  chromate  is  a  heavy  powder,  of  a  dirty  yellowish- 
brown  color.  ~It  must  evolve  no  carbon  dioxide  upon  the  applica- 
tion of  a  red  heat ;  the  evolution  of  carbon  dioxide  would  indicate 
contamination  with  organic  matter,  dust,  &c.  It  must  contain 
nothing  soluble  in  water. 

Uses. — Lead  chromate  serves,  the  same  as  cupric  oxide,  for 
the  combustion  of  organic  substances.  It  is  converted,  in  the  pro- 
cess of  combustion,  into  chromic  oxide  and  basic  lead  chromate. 
It  suffers  the  same  decomposition,  with  evolution  of  oxygen,  when 
heated  by  itself  above  its  point  of  fusion.  The  property  of  lead 
chromate  to  fuse  at  a  red  heat  renders  it  preferable  to  cupric  oxide 
as  an  oxidizing  agent,  in  cases  where  we  have  to  act  upon  difficultly 
combustible  substances. 

N.B.  Lead  chromate  may  be  used  a  second  time.  For  this 
purpose  it  is  fused  again  (being  first  roasted,  if  necessary),  and 
then  powdered.  After  having  been  twice  used  it  is  powdered, 
moistened  with  nitric  acid,  dried,  and  fused.  In  this  way  the 


§  66.]  REAGENTS.  125 

lead   chromate   may   be   used   over   and   over   agaia   indefinitely 

(VOHL*). 

3.  OXYGEN    GAS. 

Preparation. — Triturate  100  grammes  of  potassium  chlorate 
with  5  grammes  of  finely  pulverized  manganese  binoxide,  and 
introduce  the  mixture  into  a  plain  retort,  which  must  not  be  more 
than  half  full ;  expose  the  retort  over  a  charcoal  fire  or  a  gas-lamp, 
at  first  to  a  gentle,  and  then  to  a  gradually  increased  heat.  As 
soon  as  the  salt  begins  to  fuse,  shake  the  retort  a  little,  that  the 
contents  may  be  uniformly  heated.  The  evolution  of  oxygen 
speedily  commences,  and  proceeds  rapidly  at  a  relatively  low  tem- 
perature, provided  the  above  proportions  be  adhered  to.  As  soon 
as  the  air  is  expelled  from  the  retort,  connect  the  glass  tube  fixed 
in  the  neck  of  the  retort  by  means  of  a  tight-fitting  cork,  with  an 
india-rubber  tube  inserted  in  the  lower  orifice  of  the  gasometer ; 
the  glass  tube  must  be  sufficiently  wide,  and  there  must  be  sufficient 
space  left  around  the  india-rubber  to  permit  the  free  efflux  of  dis- 
placed water.  Continue  the  application  of  heat  to  the  retort  till 
the  evolution  of  gas  has  ceased.  100  grammes  of  potassium 
chlorate  give  about  27  litres  of  oxygen. 

The  oxygen  produced  by  this  process  is  moist,  and  may  con- 
tain traces  of  carbon  dioxide,  and  also  of  chlorine.  These  impuri- 
ties must  be  removed  and  the  oxygen  thoroughly  dried,  before  it 
can  be  used  in  organic  analysis.  The  gas  is  therefore  passed  from 
the  gasometer  first  through  a  solution  of  potassa  of  1'27  sp.  gr., 
then  through  U  tubes  containing  granulated  soda  lime,  and  finally, 
according  to  circumstances,  through  U  tubes  containing  calcium 
chloride  or  pumice-stone  moistened  with  sulphuric  acid. 

Tests. — A  chip  of  wood  which  has  been  kindled  and  blown  out 
so  as  to  leave  a  spark  at  the  extremity  must  immediately  burst  into 
flame  in  oxygen  gas.  The  gas  must  not  render  lime-water  or  a 
solution  of  silver  nitrate  turbid  when  transmitted  through  these 
fluids. 

4.  SODA-LIME. 

Preparation. — Take  solution  of  soda  £N"aOH),  ascertain  its 
specific  gravity,  weigh  out  a  certain  quantity,  calculate  the  weight  of 
sodium  hydroxide  present,  add  twice  this  latter  weight  of  the  best 
quick-lime,  allow  the  lime  to  slake,  and  then  evaporate  to  dryness 

*  Annalen  d.  Chem.  u.  Pharm.,  106,  127. 


126  KEAGENTS.  [§  66. 

in  an  iron  vessel.  Heat  the  residue  in  an  iron  or  Hessian  crucible  ; 
keep  for  some  time  at  a  low  red  heat.  Break  up  while  still  warm  in 
an  iron  mortar,  and  pass  the  whole  through  a  sieve  with  meshes 
about  3  mm.  wide.  Reject  the  finest  portion  (removing  it  with  a 
fine  sieve)  and  keep  the  granulated  product  in  a  well-closed 
bottle. 

JJS6t — Granulated  soda-lime  prepared  as  above  described  forms 
an  excellent  absorbent  for  carbon  dioxide.  It  was  formerly  also 
used  for  nitrogen  determination  instead  of  the  following  : 

5.  SODA-LIME  FOK  NITROGEN  DETERMINATIONS.* 
Preparation. — Equal  weights  of   sal-soda   in   clean    (washed) 

large  crystals  and  of  good  white  promptly  slaking  quick-lime  are 
separately  so  far  pulverized  as  to  pass  through  holes  of  y1^  inch, 
then  well  mixed  together,  placed  in  an  iron  pot  which  should  not 
be  more  than  half  filled,  and  gently  heated,  at  first  without  stir- 
ring. The  lime  soon  begins  to  combine  with  the  crystal  wrater  of 
the  sodium  carbonate,  the  whole  mass  heats  strongly,  swells  up,  and 
in  a  short  time  yields  a  fine  powder,  which  may  then  be  stirred  to 
effect  intimate  mixttire  and  to  drive  off  the  excess  of  water  so  that 
the  mass  is  not  perceptibly  moist  and  yet  short  of  the  point  at 
which  it  rises  in  dust  on  handling.  "When  cold  it  is  secured  in 
well-closed  bottles  or  fruit  jars,  and  is  ready  for  use. 

6.  METALLIC  COPPER. 

Metallic  copper  serves,  in  the  analysis  of  nitrogenous  substances, 
to  effect  the  reduction  of  the  nitric  oxide  gas  that  may  form  in 
the  course  of  the  analytical  process. 

It  is  used  either  in  the  form  of  turnings,  or  copper  scales 
reduced  by  hydrogen ;  or  of  small  rolls  made  of  fine  copper  wire 
gauze.  A  length  of  from  7  to  10  centimetres  is  given  to  'the 
spirals  or  rolls,  and  just  sufficient  thickness  to  admit  of  their  being 
inserted  into  the  combustion  tube.  To  have  it  perfectly  free  from 
dust,  oxide,  &c.,  it  is  first  heated  to  redness  in  the  open  air,  in  a 
crucible,  until  the  surface  is  oxidized  ;  it  is  then  put  into  a  glass  or 
porcelain  tube,  through  which  an  uninterrupted  current  of  dry 
hydrogen  gas  is  transmitted;  and  when  all  atmospheric  air  has 
been  expelled  from  the  evolution  apparatus  and  the  tube,  the 
latter  is  in  its  whole  length  heated  to  redness.  The  operator  should 

*  S.  W.  Johnson.     Report  of  the  Conn.  Agr.  Expr.  Station,  1878,  p.  111. 


§  66.]  REAGENTS.  127 

make  sure  that  the  atmospheric  air  has  been  thoroughly  expelled, 
before  lie  proceeds  to  apply  heat  to  the  tube  ;  neglect  of  this  pre- 
caution may  lead  to  an  explosion. 

7.  POTASSIUM  HYDROXIDE  OR  POTASSA. 
a.  Solution  of  Potassa. 

Solution  of  potassa  is  prepared  from  the  carbonate,  with  the 
aid  of  milk  of  lime,  in  the  way  described  in  the  "  Qualitative 
Analysis,"  for  the  preparation  of  solution  of  soda.  The  propor- 
tions are — 1  part  of  potassium  carbonate  to  12  pails  of  water,  and 
f  part  of  lime,  slaked  to  paste  with  three  times  the  quantity  of 
warm  water. 

The  decanted  clear  solution  is  evaporated,  in  an  iron  vessel, 
over  a  strong  fire,  until  it  has  a  specific  gravity  of  1*27  ;  it  is  then, 
whilst  still  warm,  poured  into  a  bottle,  which  is  well  closed,  and 
allowed  to  stand  at  rest  until  all  solid  particles  have  subsided.  The 
clear  solution  is  finally  drawn  off  from  the  deposit,  and  kept  for 
use. 

b.  Fused  Potassa  (common). 

The  commercial  potassa  in  sticks  (impure  KOH  usually  com- 
bined with  more  or  less  H2O)  will  answer  the  purpose.  If  you 
wish  to  prepare  it,  evaporate  solution  of  potassa  (a)  in  a  silver  ves- 
sel, over  a  strong  fire,  until  the  residuary  hydroxide  flows  like 
oil,  and  white  fumes  begin  to  rise  from  the  surface.  Pour  the 
fused  mass  out  on  a  clean  iron  plate,  and  break  it  up  into  small 
pieces.  Keep  in  a  well-stoppered  bottle  for  use. 

c.  Potassa  (purified  with  alcohol),  see  "  Qual.  Anal.,"  p.  43. 

Uses. — Solution  of  potassa  serves  for  the  absorption,  and  at 
the  same  time  for  the  estimation  of  carbon  dioxide.  In  many 
cases,  a  tube  filled  with  fragments  of  fused  potassa  is  used,  in 
addition  to  the  apparatus  filled  with  solution  of  potassa.  Potassa 
purified  with  alcohol,  which  is  perfectly  free  from  potassium  sul- 
phate, is  employed  for  the  determination  of  sulphur  in  organic 
substances. 

8.  CALCIUM  CHLORIDE. 

a.  Pure  Calcium  Chloride. 

Preparation. — Dissolve  marble  in  commercial  hydrochloric 
acid  diluted  with  four  or  five  times  its  volume  of  water.  (The 
waste  solution  resulting  from  the  preparation  of  carbon  dioxide 


128  KEAGENTS.  [§  66. 

\ 

may  be  used.)  Add  to  this  solution  with  stirring  lime,  slaked 
•with  sufficient  water  to  give  it  the  consistency  of  thin  paste  until 
it  gives  an  alkaline  reaction  and  a  pellicle  of  calcium  carbonate 
forms  on  the  surface  on  standing  exposed  to  the  air.  Iron,  man- 
ganese, and  especially  magnesium  are  usually  present  in  such  a 
solution,  and  are  precipitated  by  the  calcium  hydroxide — the  iron, 
however,  not  completely.  After  a  few  hours,  filter  and  pass  hydro- 
gen sulphide  through  the  alkaline  solution  until  a  filtered  portion 
is  no  longer  blackened  by  this  reagent.  Let  the  solution  stand  for 
twelve  hours,  then  filter  from  the  iron  sulphide.  Add  next  hydro- 
chloric acid  to  strongly  acid  reaction  to  convert  the  calcium  sul- 
phide and  calcium  oxy chloride  which  may  be  present  into  chloride. 
Concentrate  in  a  porcelain  dish.  If  sulphur  separates,  after  a  short 
time  filter  again,  and  continue  the  evaporation  to  dry  ness  with 
addition  of  a  little  more  hydrochloric  acid  toward  the  end  of  the 
process.  Finally  expose  the  residue  to  a  tolerably  strong  heat 
about  (200°)  on  the  sand-bath,  until  it  is  changed  throughout  to  a 
white  porous  perfectly  opaque  mass,  which  point  can  be  ascertained 
by  breaking  up  a  piece  detached  from  the  top.  The  product  is 
CaCl2  -f-  (H2O)2.  Reduce  while  still  hot  to  granules  of  the  proper 
size  (-J-  to  -^  of  an  inch)  by  means  of  suitable  sieves  and  a  mortar 
previously  warmed,  and  keep  in  well-closed  bottles. 

b.   Crude  fused  Calcium  Chloride. 

Preparation. — Neutralize  the  alkaline  solution  obtained  in  a 
(without  separating  the  little  iron  present  with  H2S)  exactly  with 
hydrochloric  acid,  and  evaporate  to  dryness  in  an  iron  pan  ;  fuse 
the  residue  in  an  iron  or  Hessian  crucible,  pour  out  the  fused  mass, 
and  break  into  pieces.  Preserve  it  in  well-stoppered  bottles. 

Uses. — The  crude  fused  calcium  chloride  serves  to  dry  moist 
gases ;  the  pure  chloride  is  used  in  elementary  organic  analysis  for 
the  absorption  and  estimation  of  water  formed  by  the  hydrogen 
contained  in  the  analyzed  substance.  A  solution  of  the  pure  cal- 
cium chloride  should  not  show  an  alkaline  reaction.  A  calcium 
chloride  tube  filled  with  it  should  not  gain  weight  when  a  very 
slow  current  of  perfectly  dry  carbon  dioxide  is  passed  through  it 
an  hour. 

9.  POTASSIUM  BICHROMATE. 

Bichromate  of  potassa  of  commerce  is  purified  by  repeated 
recry stall ization,  until  barium  chloride  produces,  in  the  solution  of 


§  66.]  REAGENTS.  129 

a  sample  of  it  in  water,  a  precipitate  which  completely  dissolves  in 
hydrochloric  acid.  Potassium  dichromate  thus  perfectly  free  from 
sulphuric  acid  is  required  more  particularly  for  the  oxidation  of 
organic  substances  with  a  view  to  the  estimation  of  the  sulphur 
contained  in  them.  "Where  the  salt  is  intended  for  other  purposes, 
e.g.,  to  determine  the  carbon  of  organic  bodies,  by  heating  them 
with  potassium  dichromate  and  sulphuric  acid,  one  recrystallization 
is  sufficient. 


SECTION    III. 

FOEMS  AND  COMBINATIONS  IN  WHICH  SUB- 
STANCES AKE  SEPAEATED  FEOM  EACH  OTHER, 
OR  IN  WHICH  THEIR  WEIGHT  IS  DETERMINED. 

§67. 

THE  quantitative  analysis  of  a  compound  substance  requires, 
as  the  first  and  most  indispensable  condition,  a  correct  and  accurate 
knowledge  of  the  composition  and  properties  of  the  new  combina- 
tions into  which  it  is  intended  to  convert  its  several  individual 
constituents,  for  the  purpose  of  separating  them  from  one  another, 
and  determining  their  several  weights.  Regarding  the  properties 
of  the  new  compounds,  we  have  to  inquire  more  particularly,  in 
the  first  place,  how  they  behave  with  solvents ;  secondly,  what  is 
their  deportment  in  the  air ;  and,  thirdly,  what  is  their  behavior  on 
ignition  ?  It  may  be  laid  down  as  a  general  rule,  that  compounds 
are  the  better  adapted  for  quantitative  determination  the  more 
insoluble  they  are,  and  the  less  alteration  they  undergo  upon 
exposure  to  air  or  to  a  high  temperature. 

With  respect  to  the  composition  of  a  compound,  it  is  better 
adapted  to  the  quantitative  determination  of  a  body  the  less  it 
contains  relatively  of  that  body  ;  since  any  error  in  weighing  or 
loss  of  the  compound  to  be  weighed  will  have  the  less  influence  on 
the  accuracy  of  the  results  the  less  the  percentage  it  contains  of 
the  substance  to  be  determined. 

In  this  section  those  combinations  of  the  several  bodies  which 
are  best  adapted  for  their  quantitative  determination  are  enumer- 
ated and  described.  The  description  given  of  the  external  form 
and  appearance  of  the  new  compounds  relates  more  particularly  to 
the  state  in  which  they  are  obtained  in  our  analyses.  With  regard 
to  the  properties  of  the  new  compounds,  we  shall  confine  ourselves 
to  the  enumeration  of  those  which  bear  upon  the  special  objects 
we  have  more  immediately  in  view. 

[The  percentage  compositions  of  these  compounds  are  stated  in 
connection  with  their  description.  For  this  purpose  the  symbols 


$  67.]  FORMULA.  131 

of  the  constituent  elements  of  the  compounds  in  many  cases 
(viz.  :  when  they  are  oxygen  salts)  are  grouped  in  a  manner 
different  from  that  used  to  express  their  chemical  constitution. 
This  grouping  constitutes  a  kind  of  formulae  differing  from  either 
the  empirical  or  rational  in  ordinary  use  in  modern  text-books  of 
chemistry,  but  identical  with  that  formerly  in  general  use  (the  old 
system).  These  formulae  are  based  upon  the  fact  that  in  all 
oxygen  salts,  whether  normal,  acid,  basic,  ortho-,  meta-,  or  pyro- 
salts,  there  is  just  enough  oxygen  to  form  with  the  radicals  present, 
both  basic  and  acid,  their  corresponding  oxides  or  anhydrides,  and 
with  hydrogen,  if  present,  water.  They  represent  oxides  (and 
water)  jointly  equivalent  in  weight  to  the  radicals,  hydrogen,  and 
remaining  oxygen,  which  rational  formulae  represent  as  existing  in 
oxygen  salts. 

EXAMPLES. 
OTT 

Potassium  sulphate,     SO2  <  QK  =  ^A^O,. 
Hydrogen  potassium  sulphate, 

8(80,  <  g|)  =  K,0,H,0,2SO, 
Potassium  disulphate, 

0  <  SO!  -  OK  =  KA2SO,. 
Ammonium  magnesium  phosphate, 

°  ^  O 

Magnesium  pyrophosphate, 

PO  <  2  >  Mg 


Most  analytical  chemists  prefer  to  present  the  results  of  analyses 
of  oxygen  salts  in  percentages  of  oxides  (or  anhydrides)  and  water 
on  account  of  the  simplicity  of  computations  required.  Accord- 


132  FORMS.  [§  68. 

ingly,  in  the  following  section,  the  percentage  composition  of 
oxygen  salts  is  given  in  this  manner,  accompanied  by  correspond- 
ing formulae  and  molecular  weights.  These  formulae  are  in  every 
case  preceded  by  rational  formulae  constructed  in  accordance  with 
the  theory  of  the  constitution  of  oxygen  salts  which  is  now 
generally  accepted.] 


A.     FORMS  IN  WHICH  THE  BASIC  RADICALS  ARE  WEIGHED  OR 

PRECIPITA  TED. 

BASIC  RADICALS   OF   THE  FIRST   GROUP. 

§68. 
1.  POTASSIUM. 

The  combinations  best  suited  for  the  weighing  of  potassium 
are  POTASSIUM  SULPHATE,  POTASSIUM  CHLORIDE,  and  POTASSIUM 

PLATINIC    CHLORIDE. 

a.  Potassium  sulphate  crystallizes  usually  in  small,  hard, 
straight,  four-sided  prisms,  or  in  double  six-sided  pyramids ;  in 
the  analytical  process  it  is  obtained  as  a  white  crystalline  mass. 
It  dissolves  with  some  difficulty  in  water  (1  part  requiring  10  parts 
of  water  of  12°),  it  is  almost  absolutely  insoluble  in  pure  alcohol, 
but  slightly  more  soluble  in  alcohol  containing  sulphuric  acid 
(Expt.  No.  6).  It  does  not  affect  vegetable  colors ;  it  is  unalter- 
able in  the  air.  The  crystals  decrepitate  strongly  when  heated, 
yielding  at  the  same  time  a  little  water,  which  they  hold  mechani- 
cally confined.  The  decrepitation  of  crystals  that  have  been  kept 
long  drying  is  less  marked.  At  a  good  red  heat  the  salt  fuses 
without  volatilizing  or  decomposing.  At  a  white  heat  a  little  of 
the  salt  volatilizes  and  also  some  sulphuric  acid,  so  that  the  residue 
possesses  an  alkaline  reaction  (AL.  MITSCHERLICH,*  BoussiNGAULTf). 
When  exposed  to  a  red  heat,  in  conjunction  with  ammonium 
chloride,  potassium  sulphate  is  partly,  and,  upon  repeated  applica- 
tion of  the  process,  wholly  converted,  with  effervescence,  into 
potassium  chloride  (H.  KOSE). 


*  Journ.  f.  prakt.  Chem.  83,  486.  f  Zeitschr.  f.  anal.  Chem.  7,  244. 


68.]  BASES    OF   GROUP   I.  133 

COMPOSITION. 

K3O  .  .  .   94-26      54-09 
~  SO,         80-00      45-91 


174-26     100-00 

The  acid  potassium  sulphate  (KHSO4),  which  is  produced  when 
the  normal  salt  is  evaporated  to  dryness  with  free  sulphuric  acid, 
is  readily  soluble  in  water,  and  fusible  even  at  a  moderate  heat. 
At  a  red  heat  it  loses  sulphuric  acid,  and  is  converted  into  normal 
potassium  sulphate,  but  not  readily — the  complete  conversion  of 
the  acid  into  the  normal  salt  requiring  the  long-continued  applica- 
tion of  an  intense  red  heat.  However,  when  heated  in  an  atmos- 
phere of  ammonium  carbonate — which  may  be  readily  procured  by 
repeatedly  throwing  into  the  faint  red-hot  crucible  containing  the 
acid  sulphate  small  lumps  of  pure  ammonium  carbonate,  and 
putting  on  the  lid — the  acid  salt  changes  readily  and  quickly  to 
the  normal  sulphate.  The  transformation  may  be  considered 
complete  as  soon  as  the  salt,  which  was  so  readily  fusible  before,  is 
perfectly  solid  at  a  faint  red  heat. 

b.  Potassium:  chloride  crystallizes  usually  in  cubes,  often 
lengthened  to  columns ;  rarely  in  octahedra.  In  analysis  we 
obtain  it  either  in  the  former  shape,  or  as  a  crystalline  mass.  It  is 
readily  soluble  in  water,  but  much  less  so  in  dilute  hydrochloric 
acid ;  in  absolute  alcohol  it  is  nearly  insoluble,  and  but  slightly 
soluble  in  common  alcohol.  It  does  not  affect  vegetable  colors, 
and  is  unalterable  in  the  air.  When  heated,  it  decrepitates,  unless 
it  has  been  kept  long  drying,  with  expulsion  of  a  little  water 
mechanically  confined  in  it.  At  a  moderate  red  heat,  it  fuses 
unaltered  and  without  diminution  of  weight ;  when  exposed  to  a 
higher  temperature,  it  volatilizes  in  white  fumes  ;  this  volatilization 
proceeds  the  more  slowly  the  more  effectually  the  access  of  air  is 
prevented  (Expt.  No.  7).  When  repeatedly  evaporated  with 
solution  of  oxalic  acid  in  excess,  it  is  converted  into  potassium 
oxalate.  When  evaporated  with  excess  of  nitric  acid,  it  is  con- 
verted readily  and  completely  into  nitrate.  On  ignition  with 
ammonium  oxalate,  potassium  carbonate  and  potassium  cyanide 
are  formed  in  noticeable  quantities. 


134  FORMS.  [§  68. 

COMPOSITION. 

K       .     .     .     .       39-13  52-46 

Cl  35-46  47-54 


74-59  100-00 

c.  Potassium  platinic  chloride  presents  either  small  reddish- 
yellow  octahedra,  or  a   lemon-colored   powder.     It   is   difficultly 
soluble  in  cold,  more  readily  in  hot  water;  nearly  insoluble  in 
absolute  alcohol,  and  but  sparingly  soluble  in  common  alcohol- 
one  part  requiring  for  its  solution,  respectively,  12083  parts  of 
absolute   alcohol,    3775    parts   of    alcohol    of    76   per   cent,    and 
1053  parts  of  alcohol  of  55  per  cent.     (Expt.  No.  8,  a.)     Presence 
of  free  hydrochloric  acid  sensibly  increases  the  solubility  (Expt. 
No.  8,  b).     In  caustic  potassa  it  dissolves  completely  to  a  yellow 
fluid.     It  is  unalterable  in  the  air,  and  at  100°.     On   exposure  to 
an  intense  red  heat,  four  atoms  of  chlorine  escape,  metallic  plati- 
num and  potassium  chloride  being  left ;  but  even  after  long-con- 
tinued fusion,  there  remains  always   a   little   potassium   platinic 
chloride  which  resists  decomposition.     Complete  decomposition  is 
easily  effected,  by  igniting  the  double  salt  in  a  current  of  hydrogen 
gas,  or  with  some  oxalic  acid. 

According  to  ANDREWS,  potassium  platinic  chloride,  even 
though  dried  at  a  temperature  considerably  exceeding  100°,  retains 
still  "0055  of  its  weight  of  water. 

COMPOSITION. 

(KC1),    .     .     .  149-18      30-56          K2     .     .     .     78-26  16-03 

PtCl4     ...  339-02       69-44          Pt     .     .     .  197-18  40-39 

01.    .     .     .  212-76  43-58 
488-20     100-00 

488-20  100-00 

d.  Potassium  silicqfluoride  is  obtained  on  mixing  a  solution  of 
a  potassium  salt  with  hydrofluosilicic  acid  in  the  form  of  a  trans- 
lucent   iridescent   precipitate,    which    increases    and    completely 
separates,  when  an  equal  volume  of  strong  alcohol  is  added  to  the 
fluid.    After  being  filtered  off,  washed  with  weak  alcohol  and  dried, 
it  is  a  soft  white  powder.     It  is  difficultly  soluble  in  cold  water,  far 
more  readily  in  boiling  water,  not  at  all  or  in  merest  traces  soluble 
in  a  mixture  of  water  and  strong  alcohol  in  equal  parts,  but  it  is 


§  69.]  BASES    OF    GROUP    I.  135 

decidedly  more  soluble  in  the  presence  of  any  considerable  quan- 
tity of  free  acid,  especially  hydrochloric  or  sulphuric  acid.  When 
potassa  is  added  to  the  boiling  aqueous  solution  of  the  salt  the 
following  change  takes  place  :  (KF)2SiF4  +  4KOH  =  6KF  + 
Si(OH)4,  the  solution  turning  from  acid  to  neutral  (principle  of 
STOLBA?S  volumetric  method  of  estimating  potassium).  As  soon  as 
it  is  ignited  the  salt  fuses,  gives  off  silicon  fluoride  and  leaves 
potassium  fluoride. 

§69. 
2.  SODIUM. 

Sodium  is  usually  weighed  as  SODIUM  SULPHATE,  SODIFM  CHLO- 
RIDE, or  SODIUM  CARBONATE.  It  is  separated  from  potassium  in  the 
form  of  SODIUM  PLATINIC  CHLORIDE,  from  other  bodies  occasionally 
in  the  form  of  sodium  silicofluoride. 

a.  Anhydrous  normal  sodium  sulphate  is  a  white  powder  or  a 
white  very  friable  mass.  It  dissolves  readily  in  water  ;  but  is 
sparingly  soluble  in  absolute  alcohol  ;  presence  of  free  sulphuric 
acid  slightly  increases  its  solubility  in  that  menstrum  ;  it  is  some- 
what more  readily  soluble  in  common  alcohol  (Expt.  No.  9).  It 
does  not  affect  vegetable  colors  ;  upon  exposure  to  moist  air,  it 
slowly  absorbs  water  (Expt.  No.  10).  At  a  gentle  heat  it  is  un- 
altered, at  a  strong  red  heat  it  fuses  without  decomposition  or  lo>s 
of  weight.  At  a  white  heat  it  loses  weight  by  volatilization  of 
sodium  sulphate  and  also  of  sulphuric  acid  (Ai..  MITSCHERLK  n, 
BOUSSINGAULT).  When  ignited  with  ammonium  chloride,  it  be- 
haves like  potassium  sulphate. 

COMPOSITION. 


OKa  _    Na,O  ....     62-08          43-69 
ONa  -  SO3      ....     80-00     .      56-31 


142-08         100-  00 

The  acid  sodium  sulphate  (sodium  hydrogen  sulphate,  NaHSO4) 
which  is  always  produced  upon  the  evaporation  of  a  solution  of  the 
normal  salt  with  sulphuric  acid  in  excess,  fuses  even  at  a  gentle 
heat  ;  it  may  be  readily  converted  into  the  normal  salt  in  the  same 
manner  as  the  acid  potassium  sulphate  (see  §  68,  a). 

b.  Sodium  chloride  crystallizes  in  cubes,  octahedra,  and  hollow 


136  FORMS.  [§  69. 

four-sided  pyramids.  In  analysis  it  is  frequently  obtained  as  an 
amorphous  mass.  It  dissolves  readily  in  water,  but  is  much  less 
soluble  in  hydrochloric  acid  ;  it  is  nearly  insoluble  in  absolute 
alcohol,  and  but  sparingly  soluble  in  common  alcohol ;  100  parts 
of  alcohol  of  75  per  cent,  dissolve,  at  a  temperature  of  15°,  '7  part 
("WAGNER).  It  is  neutral  to  Aregetable  colors.  Exposed  to  a 
somewhat  moist  atmosphere,  it  slowly  absorbs  water  (Expt.  No.  12). 
Crystals  of  this  salt  that  have  not  been  kept  drying  a  considerable 
time  decrepitate  when  heated,  yielding  a  little  water,  which  they 
hold  mechanically  confined.  The  salt  fuses  at  a  red  heat  without 
decomposition ;  at  a  white  heat,  and  in  open  vessels  even  at  a 
bright  red  heat,  it  volatilizes  in  white  fumes  (Expt.  No.  13).  If  a 
carburetted  hydrogen  name  acts  on  fusing  sodium  chloride,  hydro- 
chloric acid  escapes,  and  some  sodium  carbonate  is  formed.  On 
evaporation  with  oxalic  or  nitric  acid  as  well  as  by  ignition  with 
ammonium  oxalate,  it  behaves  like  the  corresponding  potassium 
salt. 


COMPOSITION. 


Na     .....     23-04  39-38 

Cl  35-46  60-62 


58-50  100-00 

c.  Anhydrous  sodium  carbonate  is  a  wrhite  powder  or  a  white 
very  friable  mass.  It  dissolves  readily  in  water,  but  much  less  so 
in  solution  of  ammonia  (MAEGUERITTE)  ;  it  is  insoluble  in  alcohol. 
Its  reaction  is  strongly  alkaline.  Exposed  to  the  air,  it  absorbs 
water  slowly.  On  moderate  ignition  to  incipient  fusion  it  scarcely 
loses  weight ;  on  long  fusion,  however,  it  volatilizes  to  a  consider- 
able extent  (Comp.  Expt.  14). 

COMPOSITION. 

.  ONa  _    Na2O  62-08  58-52 

-~  .     .     .      44-00  41-48 


106-08  100-00 

d.  Sodium  platinic  chloride  crystallizes  with  6  mol.  water 
(NaCl)3.  PtCl4  +  6  H2O,  in  light  yellow,  transparent,  prismatic 
crystals  which  dissolve  readily  both  in  water  and  in  common 
alcohol. 


§  70.]  BASES    OF    (iJK)UP    I.  137 

e.  Sodium  silicofluoride  is  similar  in  properties  to  the  corre- 
sponding potassium  salt.  It  has  an  analogous  composition,  and  is 
decomposed  in  the  same  way  by  alkalies.  It  is,  however,  con- 
siderably more  soluble  in  water  and  in  diluted  alcohol. 


3.  AMMONIUM. 

Ammonium  is  most  appropriately  weighed  as  AMMONIUM 
CHLORIDE,  or  as  AMMONIUM  pLATiNic  CHLORIDE,  or  it  may  be  esti- 
mated from  the  weight  of  the  PLATINUM  in  the  latter  compound. 

Under  certain  circumstances  ammonium  may  also  be  estimated 
from  the  volume  of  the  NITROGEN  GAS  eliminated  from  it  ;  and  it 
is  frequently  estimated  by  alkalimetry. 

a.  Ammonium  chloride  crystallizes  in  cubes  and  octahedra,  but 
more  frequently  in  feathery  crystals.  In  analysis  we  obtain  it 
uniformly  as  a  white  mass.  It  dissolves  readily  in  water,  but  is 
difficultly  soluble  in  common*  alcohol.  It  does  not  alter  vegetable 
colors,  and  remains  unaltered  in  the  air.  Solution  of  ammonium 
chloride,  when  evaporated  on  the  water-bath,  loses  a  small  quantity 
of  ammonia,  and  becomes  slightly  acid.  The  diminution  of  weight 
occasioned  by  this  loss  of  ammonia  is  very  trifling  (Expt.  Xo.  15). 
At  100°  ammonium  chloride  loses  nothing,  or  very  little  of  its 
weight  (comp.  same  Expt.).  At  a  higher  temperature  it  volatilizes 
readily,  and  without  undergoing  decomposition. 

COMPOSITION. 

XII  18-04         33-72  NH3     .     .     17-04          31-85 

Cl   ,  35-46         66-28  HC1     .     .     36-46          68-15 


53-50       100-00  53-50         100-00 

100*parts  of  ammonium  chloride  correspond  to  48  •  67  parts  of 
ammonium  oxide. 

J.  Ammonium  platinic  chloride  occurs  either  as  a  heavy, 
lemon-colored  powder,  or  in  small,  hard  octahedral  crystals  of  a 
bright  yellow  colon  It  is  difficultly  soluble  in  cold,  but  more 
readily  in  hot  water.  It  is  very  sparingly  soluble  in  absolute 
alcohol,  but  more  readily  in  common  alcohol — 1  part  requiring  of 
absolute  alcohol,  26535  parts;  of  alcohol  of  76  per  cent.,  14<><'> 


138  FORMS.  [§  71. 

parts;  of  alcohol  of  55  per  cent.,  665  parts.  The  presence  of 
free  acid  sensibly  increases  its  solubility  (Expt.  No.  16).  It 
remains  unaltered  in  the  air,  and  at  100°.  It  loses  a  little  water 
between  100°  and  125°.  Upon  ignition  chlorine  and  ammonium 
chloride  escape,  leaving  the  metallic  platinum  as  a  porous  mass 
(spongy  platinum).  However,  if  due  care  be  not  taken,  in  this 
process,  to  apply  the  heat  gradually,  the  escaping  fumes  will  carry 
off  particles  of  platinum,  which  will  coat  the  lid  of  the  crucible. 
For  properties  of  metallic  platinum,  see  §  89,  a. 

COMPOSITION. 

(NH4Cl)a  .     .  107-00       23-99        (NH4)2     .     .     36-08  8-09 

PtCl4    .     .     .339-02       76-01         Pt  .     .     .     .197-18  44-21 

01.      ...  212-76  47-70 

446-02     100-00  — 


446-02  100-00 

N,       ...     28-08         6-295         (NH,)S     .     .     34-08  7-64 
H8       .     .     .       8-00         1-794 

Pt       ...  197-18       44-209         (HOI),      .     .     72-92  16-35 

Ol,      .     .     .212-76       47-702        PtCl4.      .     .  339-02  76-01 


446-02     100-000  446-02     100-00 

100  parts  of  ammonium  platinic  chloride  correspond  to  11-677 
parts  of  ammonium  oxide. 

c.  Nitrogen  gas  is  colorless,  tasteless,  and  inodorous ;  it  mixes 
with  air,  without  producing  the  slightest  coloration ;  it  does  not 
affect  vegetable  colors.  Its  specific  gravity  is  -97137  (REGNAULT). 
One  litre  weighs  at  0°,  and  '76  metre  bar.,  1-25617  grm.  It  is 
difficultly  soluble  in  water,  1  volume  of  water  absorbing,  at  0°,  and 
•76  pressure,  -02035  vol.;  at  10°,  -01607  vol.;  at  15°,  -01478  vol. 
of  nitrogen  gas  (BUNSEN). 

BASIC  RADICALS  OF  THE  SECOND   GROUP.      „ 

§71. 

1.  BARIUM. 
.  Barium  is  weighed  as  BARIUM  SULPHATE/  BARIUM  CARBONATE, 

and  BARIUM  SILICOFLUORIDE. 

a.  Artificially  prepared  'barium  sulphate  presents  the  appear- 
ance is  of  a  fine  white  powder.  When  recently  precipitated,  it 


£  71.]  BASES    OF    GROUP   II.  139 

difficult  to  obtain  a  clear  filtrate,  especially  if  the  precipitation  was 
effected  in  the  cold,  and  the  solution  contains  neither  hydrochloric 
acid  nor  ammonium  chloride.  It  is  as  good  as  insoluble  in  cold 
and  in  hot  water.  (1  part  of  the  salt  requires  more  than  400,<  ><  ><  > 
parts  of  water  for  solution.)  It  has  a  great  tendency,  upon  pre- 
cipitation, to  carry  down  with  it  other  substances  contained  in  the 
solution  from  which  it  separates,  more  particularly  barium  nitrate, 
nitrates  and  chlorates  of  the  alkali  metals,  ferric  oxide,  &c.  Several 
of  the  impurities,  such,  for  instance,  as  potassium  or  sodium  chlo- 
rates, may  be  removed  by  igniting  the  barium  sulphate,  moistening 
with  hydrochloric  acid,  evaporating  the  latter  off  and  exhausting 
the  residue  with  water ;  other  impurities  again,  such  as  potassium 
or  sodium  nitrates,  cannot  be  removed"  by  this  treatment.  Even 
the  precipitate  obtained  from  a  solution  of  barium  chloride  by 
means  of  sulphuric  acid  in  excess  contains  traces  of  barium  chloride, 
which  it  is  impossible  to  remove,  even  by  washing  with  boiling 
water,  but  which  are  dissolved  by  nitric  acid  (SIEGLE).  Cold  dilute 
acids  dissolve  trifling,  yet  appreciable  traces  of  barium  sulphate ; 
for  instance,  1000  parts  of  nitric  acid  of  1/032  sp.  giv  dissolve  '062 
parts  (CALVERT).  1000  parrs  of  hydrochloric  acid  containing  3  per 
cent,  dissolve  •()(>  parts.*  Cold  concentrated  acids  dissolve  consid- 
erably more ;  thus,  1000  parts  of  nitric  acid  of  1'167  sp.  gr.  dis- 
solve 2  parts  (CALVERT).  Boiling  hydrochloric  acid  also  dissolves 
appreciable  traces;  thus  230  c.c.  hydrochloric  acid  of  1/02. sp.  gr. 
were  found,  after  a  quarter  of  an  hour's  boiling  with  '679  grm. 
barium  sulphate,  to  have  dissolved  of  it  -048  grm.  Acetic  acid 
dissolves  less  barium  sulphate  than  the  other  acids;  thus,  80  c.c. 
acetic  acid  of  1*02  sp.  gr.  were  found,  after  a  quarter  of  an  hour's 
boiling  with  ••!  grm.,  to  have  dissolved  only  -002  grm.  (SIEGLE). 
Free  chlorine  considerably  increases  its  solubility  (O.  L.  ERDMANN). 
Several  salts  more  particularly  interfere  with  the  precipitation  of 
barium  by  sulphuric  acid.  I  observed  this  some  time  ago  with 
magnesium  chloride,  but  ammonium  nitrate  (MITTENTZWEY),  alkali 
nitrates  generally,*  and  more  particularly  alkali  citrates  (SPILLER), 
possess  this  property  in  a  high  degree.  In  the  last  case  the  pre- 
cipitate appears  on  the  addition  of  hydrochloric  acid.  If  a  fluid 
contains  metaphosphoric  acid,  barium  cannot  be  completely  pre- 
cipitated out  of  it  by  means  of  sulphuric  acid  ;  the  resulting  pre- 
cipitate too  contains  phosphoric  acid  (SCHEERER,  RUBE).  Barium 
*  Zeitschr.  f .  anal.  Chem.  9,  62. 


140  FOKMS.  [§71. 

sulphate  dissolves  in  tolerable  quantity  in  concentrated  sulphuric 
acid,  but  separates  again  on  dilution.  It  is  as  good  as  insoluble 
in  a  boiling  solution  of  ammonium  sulphate  (1  in  4).  Barium 
sulphate  remains  quite  unaltered  in  the  air,  at  100°,  and  even  at 
a  red  heat.  At  a  strong  white  heat  it  loses  sulphuric  acid  (Bous- 
SINGAULT).*  On  ignition  with  charcoal,  or  under  the  influence  of 
reducing  gases,  it  is  converted  comparatively  easily,  but  as  a  rule 
only  partially,  into  barium  sulphide.  On  ignition  with  ammonium 
chloride,  barium  sulphate  undergoes  partial  decomposition.  It  is 
not  affected,  or  affected  but  very  slightly,  by  cold  solutions  of  the 
hydrogen  carbonates  of  the  alkali  metals  or  of  ammonium  carbo- 
nate ;  solutions  of  normal  sodium  and  potassium  carbonates  when 
cold  have  only  a  slight  decomposing  action  upon  it ;  but  when 
boiling,  and  upon  repeated  application,  they  effect  at  last  the 
complete  decomposition  of  the  salt  (H.  KOSE).  By  fusion  with 
sodium  or  potassium  carbonate,  barium  sulphate  is  readily  decom- 
posed. 

COMPOSITION. 

Ba°     ....     153  65.67 

go  80  34.33 


233  100-00 

1).  Artificially  prepared  barium  carbonate  presents  the  appear- 
ance of  a  white  powder.  It  dissolves  in  14137  parts  of  cold,  and  in 
15421  parts  of  boiling  water  (Expt.  No.  17).  It  dissolves  far  more 
readily  in  solutions  of  ammonium  chloride  or  ammonium  nitrate ; 
from  these  solutions  it  is,  however,  precipitated  again,  though  not 
completely,  by  caustic  ammonia.  In  water  containing  free  carbonic 
acid,  barium  carbonate  dissolves  to  an  acid  carbonate.  In  water  con- 
taining ammonia  and  ammonium  carbonate,  it  is  nearly  insoluble, 
one  part  requiring  about  141000  parts  (Expt.  No.  18).  Its  solution 
in  water  has  a  very  faint  alkaline  reaction.  Alkali  citrates  and 
metaphosphates  impede  the  precipitation  of  barium  by  ammonium 
carbonate.  It  is  unalterable  in  the  air,  and  at  a  red  heat.  When 
exposed  to  the  strongest  heat  of  a  blast-furnace,  it  slowly  yields  up 
the  whole  of  its  carbonic  acid  ;  this  expulsion  of  the  carbonic  acid 
is  promoted  by  the  simultaneous  action  of  aqueous  vapor.  Upon 
heating  it  to  redness  with  charcoal,  caustic  baryta  is  formed,  with 
evolution  of  carbon  monoxide. 

*  Zeitschr.  f.  anal.  Chem.  7,  244. 


§72.]  BASES   OF   GROUP   II.  141 

COMPOSITION. 

O^-R         BaO      .     .     .          153  77-67 

0>tJa-CO3      ....       44  22-33 


197  100-00 

c.  Itarium  silicofiuoride  forms  small,  hard,  and  colorless  crys- 
tals, or  (more  generally)  a  crystalline  powder.  It  dissolves  in  3800 
parts  of  cold  water ;  in  hot  water  it  is  more  readily  soluble  (Expt. 
No.  19).  The  presence  of  free  hydrochloric  acid  increases  its  solu- 
bility considerably  (Expt.  No.  20).  Ammonium  chloride  acts  also 
in  the  same  way  (1  part  silicofluoride  of  barium  dissolves  in  428 
parts  of  saturated,  and  589  parts  of  dilute  solution  of  ammonium 
chloride.  J.  "W.  MALLET).  In  common  alcohol  it  is  almost  insoluble. 
It  is  unalterable  in  the  air,  and  at  100° ;  when  ignited,  it  is  decom- 
posed into  silicon  fluoride,  which  escapes,  and  barium  fluoride, 
which  remains. 

COMPOSITION. 

BaFa     .     .     .     175      62-72        Ba     .     .     .     137      49-10 
SiF4      ...     104      37-28        Si     ...       28      10-04 

F.     .     .     .     114      40-86 


279    100-00 


279    100-00 


§72. 

2.  STRONTIUM. 
Strontium   is  weighed  either  as   STRONTIUM   SULPHATE,  or  as 

STRONTIUM  CARBONATE. 

a.  Strontium  sulphate,  artificially  prepared,  is  a  white  powder, 
sometimes  dense  arid  crystalline,  sometimes  loose  and  bulky.  It 
dissolves  in  6895  parts  of  cold,  and  9638  parts  of  boiling  water 
{Expt.  No.  21).  In  water  containing  sulphuric  acid,  it  is  still  more 
difficultly  soluble,  requiring  from  11000  to  12000  parts  (Expt.  No: 
22).  Of  cold  hydrochloric  acid  of  8-5  per  cent.,  it  requires  474  parts  ; 
of  cold  nitric  acid  of  4'8  per  cent.,  432  parts ;  of  cold  acetic  acid  of 
15-6  percent,  of  HC2H3Oa,  as  much  as  7843  parts  (Expt.  No.  23). 
It  dissolves  in  solutions  of  potassium  chloride  and  magnesium  chlo- 
ride, in  quantity  which  increases  with  the  concentration,  also  in  solu- 
tions of  sodium  chloride  and  calcium  chloride  in  greatest  quantity 


142  FORMS.  [§  72. 

when  the  solutions  are  of  medium  concentration  (A.  VIRCK*)  ;  it 
it  is  precipitated  from  these  solutions  by  sulphuric  acid.  Meta- 
phosphoric  acid  (SCHEEBEB,  RUBE),  and  also  alkali  citrates,  but  not 
free  citric  acid  (SPILLEK),  impede  the  precipitation  of  strontium  by 
sulphuric  acid.  It  is  as  good  as  insoluble  in  absolute  alcohol,  in 
common  alcohol,  and  in  a  boiling  solution  of  ammonium  sulphate 
(1  in  4).  It  does  not  alter  vegetable  colors  ;  and  remains  unaltered 
in  the  air,  and  at  a  red  heat.  When  exposed  to  a  most  intense  red 
heat,  it  fuses,  with  loss  of  a  small  quantity  of  sulphuric  acid  (M.  , 
DAKMSTADT  f)  ;  all  the  sulphuric  acid  will  escape  on  very  strong 
ignition  continued  for  a  length  of  time  (BOUSSINGAULT  $).  When 
ignited  with  charcoal,  or  under  the  influence  of  reducing  gases,  it 
is  converted  into  strontium  sulphide.  Solutions  of  acid  and  nor- 
mal carbonates  of  potassium,  sodium,  and  ammonium  decompose 
strontium  sulphate  completely  at  the  common  temperature,  even 
when  considerable  quantities  of  alkali  sulphates  are  present  (H. 
HOSE).  Boiling  promotes  the  decomposition. 

COMPOSITION. 

/O  _SrO  103-5  56-40 

'U*<O-        -S0      .     .     .       80-0  43-60 


183-5  100-00 

1).  Strontium,  carbonate,  artificially  prepared,  is  a  white,  soft, 
loose  powder.  It  dissolves,  at  the  common  temperature,  in  18045 
parts  of  water  (Expt.  No.  24)  :  presence  of  ammonia  diminishes 
its  solubility  (Expt.  No.  25).  It  dissolves  pretty  readily  in  solu- 
tions of  ammonium  chloride  and  ammonium  nitrate,  but  is  precipi- 
tated again  from  these  solutions  by  ammonia  and  ammonium  car- 
bonate, and  more  completely  than  barium  carbonate  under  similar 
circumstances.  Water  impregnated  with  carbonic  acid  dissolves  it 
as  an  acid  carbonate.  Its  reaction  is  very  feebly  alkaline.  Alkali 
•citrates  and  metaphosphates  impede  the  precipitation  of  strontium 
by  alkali  carbonates.  Ignited  with  access  of  air  it  is  infusible, 
but  when  exposed  to  a  most  intense  heat,  it  fuses  and  gradually 
loses  its  carbonic  acid.  On  ignition  with  charcoal,  strontium  oxide 
is  formed,  with  evolution  of  carbon  monoxide  gas. 

*  Zeitschr.  f.  anal.  Chem.  1,  473.  f  Ib-  6,  376.  J  Ib.  7,  244. 


§  73.]  BASES    OF   GROUP   II.  143 

COMPOSITION. 

SrO  .  .  .  103-50     70-17 
44-00     29-83 


147-50          100-00 

§73. 
3.  CALCIUM. 

Calcium  is  weighed  either  as  CALCIUM  SULPHATE,  CALCIUM  CAR- 
BONATE, or  CALCIUM  OXIDE;  to  convert  it  into  the  latter  forms,  it 
is  first  usually  precipitated  as  calcium  oxalate. 

a.  Artificially  prepared  anhydrous  calcium  sulphate  is  a  loose, 
white  powder.  It  dissolves,  at  the  common  temperature,  in  430 
parts,  at  100°,  in  460  parts  of  water  (POGGIALE).  Presence  of 
hydrochloric  acid,  nitric  acid,  ammonium  chloride,  sodium  sulphate, 
or  sodium  chloride,  increases  its  solubility.  It  dissolves  with  com- 
parative ease,  especially  on  gently  warming,  in  aqueous  solution  of 
sodium  thiosulphate  (DIEHL),  and  also  in  a  boiling  solution  of 
ammonium  sulphate  (1  in  4).  The  aqueous  solution  of  calcium 
sulphate  does  not  alter  vegetable  colors.  In  alcohol  of  90  per  cent 
or  stronger  it  is  almost  absolutely  insoluble.  Exposed  to  the  air, 
it  slowly  absorbs  water.  It  remains  unaltered  at  a  dull-red  heat. 
Heated  to  intense  bright  redness,  it  fuses,  losing  .weight  consider- 
ably from  loss  of  sulphuric  acid  (AL.  MITSCHERLICH  *).  On  long 
ignition  at  a  white  heat  all  the  sulphuric  acid  escapes  (Boussix- 
GAULTf).  On  ignition  with  charcoal,  or  under  the  influence  of 
reducing  gases,  it  is  converted  into  calcium  sulphide.  Solutions 
of  normal  and  acid  carbonates  of  the  alkali  metals  decompose  cal- 
cium sulphate  more  readily  still  than  strontium  sulphate. 

COMPOSITION. 

^O  .    n     _  CaO     ....     56  41-18 

lUa<O"          ~  SO3      .     .     .     .     80  58-82 


136  100-00 

b.  Calcium  carbonate  artificially  produced  by  the  precipitation 
of  a  calcium  salt  with  ammonium  carbonate  is  at  first  loose  and 

*  Jour.  f.  prakt.  Chem.  83,  485.  f  Zeitschr.  f.  anal.  Chem.  7,  244. 


144  FORMS.  [§  73. 

amorphous,  but  after  some  time  becomes  a  white,  fine,  crystal- 
line powder,  which  under  the  microscope  has  sometimes  the  form 
of  calcite,  sometimes  that  of  aragonite.  It  is  very  slightly  solu- 
ble in  water.  By  protracted  boiling  1  litre  of  water  dissolves 
*034  grm.,  according  to  A.  W.  HOFMANN,  or  "036  grin,  according 
to  C.  WELTZIEN  ;  so  one  part  requires  28500  parts  of  water  for 
solution.  The  solution  has  a  barely-perceptible  alkaline  reaction. 
In  water  containing  ammonia  and  ammonium  carbonate  the  crys- 
tallized salt  dissolves  much  more  sparingly  (Expt.  No.  27),  one 
part  requiring  about  65000  parts ;  this  solution  is  not  precipitated 
by  ammonium  oxalate.  Amorphous  calcium  carbonate  is  also 
much  more  insoluble  in  water  containing  ammonia  than  in  pure 
water  (DIVERS*).  Presence  of  ammonium  chloride  and  of  ammo- 
nium nitrate  increases  the  solubility  of  calcium  carbonate  ;  but  the 
salt  is  precipitated  again  from  these  solutions  by  ammonia  and 
ammonium  carbonate,  and  more  completely  than  barium  carbonate 
under  similar  circumstances.  Normal  salts  of  potassium  and  sodium, 
and  also  normal  calcium  and  magnesium  salts  (HUNT),  likewise 
increase  its  solubility,  the  precipitation  of  calcium  by  the  alkali 
carbonates  is  completely  prevented  or  considerably  interfered  with 
by  the  presence  of  alkali  citrates  (SPILLER)  or  metaphosphates 
(RUBE).  Water  impregnated  with  carbonic  acid  dissolves  calcium 
carbonate  as  acid  carbonate.  Calcium  carbonate  remains  unaltered 
in  the  air  at  100°,  and  even  at  a  low  red  heat ;  but  upon  the  appli- 
cation of  a  stronger  heat,  more  particularly  with  free  access  of  air, 
it  gradually  loses  its  carbonic  acid.  By  means  of  a  gas  blowpipe- 
lamp,  calcium  carbonate  (about  '5  grm.),  in  an  open  platinum 
crucible,  is  without  difficulty  reduced  to  calcium  oxide ;  attempts 
to  effect  complete  reduction  over  a  spirit  lamp  with  double  draught 
have,  however,  failed  (Expt.  No.  28).  It  is  decomposed  far  more 
readily  when  ignited  with  charcoal,  giving  off  its  carbonic  acid  in 
the  form  of  carbon  monoxide. 

COMPOSITION. 

°\n     _  CaO     ....     56  56-00 

O"   Ca-C0,     .     .     .     .     44  44-00 


100  100-00 


*  Jour.  Chem.  Soc.  1870,  362. 


§73.]  BASP:S  OF  <;uorp  n.  145 

c.  Calcium  oxalate,  precipitated  from  hot  or  concentrated  solu- 
tions, is  a  fine  white  powder  consisting  of  infinitely  minute  indis- 
tinct crystals,  and  almost  absolutely  insoluble  in  water.  The  salt 
has  the  formula,  CaCaO4  +  H2O.  When  precipitated  from  cold, 
extremely -dilute  solutions,  the  salt  presents  a  more  distinctly  crys- 
talline appearance,  and  consists  of  a  mixture  of  CaC2O4  -f-  HaO  and 
CaCaO4  +3.HaO  (SorciiAY  and  LK.\S>I;M.  Presence  of  free  oxalic 
acid  and  acetic  acid  slightly  increases  the  solubility  of  calcium 
oxalate.  The  stronger  acids  (hydrochloric  acid,  nitric  acid)  dissolve 
it  readily ;  from  these  solutions  it  is  precipitated  again  unaltered, 
by  alkalies,  and  also  (provided  the  excess  of  acid  be  not  too  great) 
by  alkali  oxalates  or  acetates  added  in  excess.  Calcium  oxalate 
does  not  dissolve  in  solutions  of  potassium  chloride,  sodium  chlo- 
ride, ammonium  chloride,  barium  chloride,  calcium  chloride,  and 
strontium  chloride,  even  though  these  solutions  be  hot  and  concen- 
trated ;  but,  on  the  other  hand,  it  dissolves  readily  and  in  appreci- 
able quantities,  in  hot  solutions  of  the  salts  belonging  to  the  mag- 
nesium group.  From  these  solutions  it  is  reprecipitated  by  an 
excess  of  alkali  oxalate  (SOUCHAY  and  LENSSEN).  Alkali  citrates 
(SPILLER)  and  metaphosphates  (RUBE)  impede  the  precipitation  of 
lime  by  alkali  oxalates.  When  treated  with  solutions  of  many  of 
the  heavy  metals,  e.g.,  with  solution  of  cupric  chloride,  silver 
nitrate,  tfcc.,  calcium  oxalate  suffers  decomposition,  a  soluble  cal- 
cium salt  being  formed,  and  an  oxalate  of  the  heavy  metal,  which 
separates  immediately,  or  after  some  time  (REYNOSO).  Calcium 
oxalate  is  unalterable  in  the  air,  and  at  100°.  Dried  at  the  latter 
temperature,  it  has  invariably  the  following  composition  (Expt.  No. 
28,  also  SOUCHAY  and  LENSSEN  *). 

CO-OV  CaO     ...     56  38-36 

|  X  Ca  -1-  H,0  =  C203    ...     72  49-32 

CO-O/  H,O     ...     18  12-32 

146  100-00 

At  205°  calcium  oxalate  loses  its  water,  without  undergoing 
decomposition ;  at  a  somewhat  higher  temperature,  still  scarcely 
reaching  dull  redness,  the  anhydrous  salt  is  decomposed,  without 
actual  separation  of  carbon,  into  carbon  monoxide  and  calcium 
carbonate.  The  powder,  which  was  previously  of  snowy  whiteness, 

*  Anal.  d.  Chem.  und  Pharm.  100,  322. 


146  FORMS.  [_§  74. 

transiently  assumes  a  gray  color  in  the  course  of  this  process,  even 
though  the  oxalate  be  perfectly  pure.  Upon  continued  applica- 
tion of  heat  this  gray  color  disappears  again.  If  the  calcium 
oxalate  is  heated  in  small,  coherent  fragments,  such  as  are  obtained 
upon  drying  the  precipitated  salt  on  a  filter,  the  commencement 
and  progress  of  the  decomposition  can  be  readily  traced  by  this 
transient  appearance  of  gray.  If  the  process  of  heating  be  con- 
ducted properly,  the  residue  will  not  contain  a  trace  of  calcium 
oxide.  Hydrated  calcium  oxalate  exposed  suddenly  to  a  dull-red 
heat,  is  decomposed  with  considerable  separation  of  carbon.  By 
ignition  over  the  gas  blowpipe  calcium  oxalate  is  converted  into 
calcium  oxide. 

d.  Calcium  oxide  obtained  by  continued  strong  ignition  of  the 
oxalate  or  carbonate  appears  as  a  white,  infusible  powder,  unalter- 
able by  ignition.  By  standing  in  the  air  it  attracts  water  and  car- 
bonic acid,  but  not  rapidly  enough  to  interfere  with  accurate 
weighing.  By  treatment  with  a  little  water  calcium  hydroxide  is 
formed  with  evolution  of  much  heat ;  on  igniting  again  the  water 
of  hydration  is  readily  and  completely  removed.  Pure  calcium 
oxide  dissolves  in  dilute  hydrochloric  acid  with  evolution  of  heat, 
but  without  effervescence. 


§Y4. 
4.  MAGNESIUM. 

Magnesium  is  weighed  as  MAGNESIUM  SULPHATE,  MAGNESIUM 
PYKOPHOSPHATE,  or  MAGNESIUM  OXIDE.  To  convert  it  into  the  pyro- 
phosphate,  it  is  precipitated  as  NORMAL  AMMONIUM  MAGNESIUM  PHOS- 
PHATE. 

a.  Anhydrous  magnesium  sulphate  presents  the  appearance  of 
a  white,  opaque  mass.  It  dissolves  readily  in  water.  It  is  nearly 
altogether  insoluble  in  absolute  alcohol,  but  it  is  somewhat  soluble 
in  common  alcohol. 

It  does  not  alter  vegetable  colors.  Exposed  to  the  air  it  absorbs 
wrater  rapidly.  At  a  moderate  red  heat,  it  remains  unaltered  ;  but 
when  heated  to  intense  redness,  it  undergoes  partial  decomposition, 
losing  part  of  its  acid,  after  which  it  is  no  longer  perfectly  soluble 
in  water.  By  means  of  a  gas  blowpipe  it  as  tolerably  easy  to  expel 


S$  74.]  BASKS  OF  <;iiorp  n.  147 

the  whole  of  the  sulphuric  acid  from  small  quantities  of  magne- 
sium sulphate  (Expt.  No.  30).  Ignited  with  ammonium  chloride 
magnesium  sulphate  is  not  decomposed. 

COMPOSITION. 

so   /O     M        MgO     ....     40  33-33 

'0'<0>MS-S03       ....     80  66-67 

120  100-00 

b.  Ammonium  magnesium  phosphate  is  a  white  crystalline 
powder.  It  dissolves,  at  the  common  temperature,  in  15293  parts 
of  cold  water  (Expt.  Xo.  31).  In  water  containing  ammonia,  it  is 
much  more  insoluble.  1000  grm.  of  a  mixture  of  3  parts  water 
and  1  part  ammonia  solution,  dissolved  only  a  quantity  correspond- 
ing to  '004  grm.  pyrophosphate  (KISSEL*)  ;  the  salt  was  consid- 
erably more  soluble  when  ammonium  chloride  was  also  present ; 
thus,  in  one  of  KISSEL'S  experiments  a  quantity  corresponding  to 
•Oil  grm.  pyrophosphate  wTas  dissolved  by  1000  grm.  fluid  con- 
taining IS  grm.  ammonium  chloride.  Presence  of  excess  of  mag- 
nesium sulphate  diminishes  the  solubility  in  dilute  ammonia,  even 
in  the  presence  of  ammonium  chloride,  to  such  an  extent  that  the 
quantity  dissolved  by  1000  grm.  fluid  cannot  be  estimated  (KISSEL); 
the  precipitate,  under  these  circumstances,  is  liable,  especially  in 
the  absence  of  much  ammonium  chloride,  and  when  a  large  excess 
of  magnesium  sulphate  is  present,  to  contain  some  magnesium 
hydroxide  or  basic  magnesium  sulphate  (KuBEL,f  KISSEL).  Sodium 
phosphate  also  diminishes  (to  about  the  same  extent  as  magnesium 
sulphate)  the  solubility  of  the  salt  in  water  containing  ammonium 
chloride  and  ammonia  (W.  HEINTZ  :£).  It  dissolves  readily  in  acids, 
even  in  acetic  acid.  Its  composition  is  expressed  by  the  formula 
XII4MgPO4  +  6H2O.  5  mol.  of  water  escape  at  100°,  the  remain- 
ing water  together  with  ammonia  are  expelled,  at  a  red  heat,  leav- 
ing Mg2P2O7.  On  the  application  of  a  stronger  heat  the  mass 
passes  through  a  state  of  incandescence,  if  the  salt  were  pure ;  the 
weight  of  the  residue  is  not  affected.  The  incandescence  may  not 
take  place  at  all  in  the  presence  of  small  quantities  of  calcium  salts, 


*  Zeitschr.  f.  anal.  Chem.  8,  173.  f  Ib.  8,  125.  \  Ib.  9, 16. 


148  FOKM-S.  [§  74. 

of  other  magnesium  salts,  or  of  silicic  acid.  It  is  occasioned  not 
by  the  passage  of  the  orthophosphate  into  the  pyrophosphate,  but 
by  the  passage  from  the  crystalline  to  the  amorphous  condi- 
tion (O.  POPP*).  If  ammonium  magnesium  phosphate  is  dissolved 
in  dilute  hydrochloric  or  nitric  acid  and  ammonia  be  then  added 
to  the  solution,  the  salt  is  reprecipitated  completely,  or  more  cor- 
rectly, only  so  much  remains  in  solution  as  corresponds  to  its 
ordinary  solubility  in  water  containing  ammonia  and  ammonium 
salt. 

c.  Magnesium  pyrophoyphcvte  presents  the  appearance  of  a 
white  mass,  often  slightly  inclining  to  gray.  It  is  barely  soluble  in 
water,  but  readily  so  in  hydrochloric  acid,  and  in  nitric  acid.  It 
remains  unaltered  in  the  air,  and  at  a  red  heat  \.  at  a  very  intense 
heat  it  fuses  unaltered.  Exposed  at  a  white  heat  to  the  action  of 
hydrogen,  Mg3(PO4)2  is  formed,  while  PH3,  P  and  P.2O3  escape. 
3(Mg2P207)  =  2(Mg,(P04)1  +  P.O.  (STRuvEf).  It  leaves  the  color 
of  moist  turmeric-,  and  of  reddened  litmus-paper  unchanged.  If 
we  dissolve  it  in  hydrochloric  or  nitric  acid,  add  water  to  the  solu- 
tion, boil  for  some  time,  and  then  precipitate  wi.h  ammonia  in 
excess,  we  obtain  a  precipitate  of  ammonium  magnesium  phosphate 
which,  after  ignition,  affords  less  Mg2P2O7,  than  was  originally 
employed.  WEBEB  J  gives  the  loss  as  from  1-3  to  2'3  per  cent. 
By  long-continued  fusion  with  mixed  potassium  and  sodium  car- 
bonates, magnesium  pyrophosphate  is  completely  decomposed,  the 
pyrophosphoric  acid  being  re-converted  into  orthophosphoric.  If, 
therefore,  we  treat  the  fused  mass  with  hydrochloric  acid,  and  then 
add  water  and  ammonia,  we  re-obtain  on  igniting  the  precipitate 
the  whole  quantity  of  the  salt  used.  If  the  solution  of  magnesium 
pyrophosphate  in  nitric  acid  is  evaporated  to  dryness  a  white  resi- 
due is  left ;  if  this  is  heated  more  strongly  hyponitric  acid  is  liber- 
ated, and  the  residue  turns  the  color  of  cinnamon  ;  on  cooling  it  is 
yellowish-white.  By  heating  still  more  strongly  to  incipient  red- 
ness, rapid  decomposition  sets  in,  more  hyponitric  acid  is  evolved, 
and  pure-white  magnesium  pyrophosphate  is  left.  Unless  the  heat 
is  applied  with  care  the  evolution  of  gas  may  be  so  rapid  as  to 
carry  away  particles  of  the  substance  (E.  LUCK). 


*  Zeitschr.  f.  anal.  Chem.  13,  305.  |  Jour.  f.  prakt.  Chem.  79,  349. 

\  Pogg.  Ann.  73, 146. 


§75.]  BASES  OF  <;non>  in.  149 


p        ( ) 

VO^  J  ^_2MgO     .     .     .      So  36-04 

V/       N.  /~\  T~»    /"  v  -t     t     *.  .^^       ^   ~ 


L'L^         100-00 

<:/.  Magnesium  oxide  is  a  white,  light,  loose  powder.  It  dis- 
solves in  55,368  parts  of  cold,  and  in  the  same  proportion  of  boil- 
ing water  (Expt.  2so.  37).  Its  aqueous  solution  has  a  very  slightly 
alkaline  reaction.  It  dissolves  in  hydrochloric  and  in  other  acids, 
without  evolution  of  gas.  Magnesium  oxide  dissolves  readily  and 
in  quantity,  in  solutions  of  normal  ammonium  salts,  and  also  in 
solutions  of  potassium  chloride  and  sodium  chloride  (Expt.  No. 
38)  and  potassium  sulphate  and  sodium  sulphate  (It.  WARIXGTON, 
Jr.)  it  is  more  soluble  than  in  water.  Exposed  to  the  air,  it  slowly 
absorbs  carbonic  acid  and  water.  Magnesium  oxide  is  highly  infusi- 
ble, remaining  unaltered  at  a  strong  red  heat,  and  fusing  super- 
ficially only  at  the  very  highest  temperature. 

<  OM  POSITION. 

Mg 24  60 

O        16  40 

40  100 

BASIC  RADICALS  OF  THE  THIRD  GROUP; 

§  T5. 
1.  ALUMINIUM. 

Aluminium  is  usually  precipitated  as  HYDROXIDE,  occasionally  as 
BASIC  ACETATE  or  BASIC  FORMATE,  and  always  weighed  as  ALUMINIUM 
OXIDE. 

ft.  Aluminium  hydroxide,  recently  precipitated  from  a  solu- 
tion of  an  aluminium  salt  by  an  alkali  is  translucent,  and  when 
dried  at  100°  has  the  formula,  A12(OH)6.  The  precipitate  inva- 
riably retains  a  minute  proportion  of  the  acid  with  which  the 
aluminium  was  previously  combined,  as  well  as  of  the  alkali  which 
has  served  as  the  precipitant ;  it  is  freed  with  difficulty  from  these 
admixtures  by  repeated  washing.  It  is  insoluble  in  pure  water ; 


150  FORMS.  [§  75. 

but  it  readily  dissolves  in  soda,  potassa,  and  ethylamine  (SONNEN- 
BCHEIN)  ;  it  is  sparingly  soluble  in  ammonia,  and  insoluble  in  am- 
monium carbonate ;  presence  of  ammonium  salts  greatly  diminishes 
its  solubility  in  ammonia  (Expt.  No.  39).  The  correctness  of  this 
statement  of  mine  in  the  first  edition  of  the  present  work,  has 
been  amply  confirmed  since  by  MALAGUTI  and  DUBOCHER  ;*  and 
also  by  experiments  made  by  my  former  assistant,  Mr.  J.  FUCHS. 
The  former  chemists  state  also  that,  when  a  solution  of  aluminium 
is  precipitated  with  ammonium  sulphide,  the  fluid  may  be  filtered 
off  five  minutes  after,  without  a  trace  of  aluminium  in  it.  FUCHS 
did  not  find  this  to  be  the  case  (Expt.  No.  40).  Aluminium 
hydroxide,  recently  precipitated,  dissolves  readily  in  hydrochloric 
or  nitric  acid ;  but  after  filtration,  or  after  having  remained  for 
some  time  in  the  fluid  from  which  it  has  been  precipitated,  it 
does  not  dissolve  in  these  acids  without  considerable  difficulty, 
and  long  digestion.  Aluminium  hydroxide  shrinks  considerably 
on  drying,  and  then  presents  the  appearance  of  a  hard,  translucent, 
yellowish,  or  of  a  white,  earthy  mass.  When  ignited,  it  loses 
water,  and  this  loss  is  frequently  attended  with  slight  decrepitation, 
arid  invariably  with  considerable  diminution  of  bulk.  Aluminium 
hydroxide  precipitated  .from  a  solution  of  aluminium  in  potassa  or 
soda  by  ammonium  chloride  is  milk-white,  denser,  easier  to  wash, 
and  much  less  soluble  in  ammonia  than  the  variety  above  de- 
scribed. When  dried  at  100°,  it  has  the  formula  A12O3  +  (HaO)a 
(J.  LowEf). 

b.  Aluminium  oxide  or  alumina,  prepared  by  heating  the 
hydroxide  to  a  moderate  degree  of  redness,  is  a  loose  and  soft  mass ; 
but  upon  the  application  of  a  very  intense  degree  of  heat,  it  con- 
cretes into  small,  hard  lumps.  At  the  most  intense  white  heat,  it 
fuses  to  a  clear  glass.  Ignited  alumina  is  dissolved  by  dilute  acids 
with  very  great  difficulty ;  in  fuming  hydrochloric  acid,  it  dis- 
solves upon  long-continued  digestion  in  a  warm  place,  slowly,  but 
completely.  It  dissolves  tolerably  easily  and  quickly  by  first  heat- 
ing with  a  mixture  of  8  parts  of  concentrated  sulphuric  acid  and 
3  parts  of  water,  and  then  adding  water  (A.  MITSCHERLICH^). 
Ignition  in  a  current  of  hydrogen  gas  leaves  it  unaltered.  By 
fusion  with  potassium  disulphate,  it  is  rendered  soluble  in  water. 
Upon  igniting  alumina  with  ammonium  chloride,  aluminium 

*  Ann.  de  Chim.  et  de  Phys.  3  Ser.  17,  421. 

f  Zeitschr.  f.  anal.  Chem.  4,  350.  J  Journ.  f.  prakt.  Chem.  81,  110. 


§70).]  BASES    OF    GROTP    III.  151 

chloride  escapes  ;  but  the  process  fails  to  effect  complete  volatili- 
zation of  the  alumina  (H.  ROSE).  When  alumina  is  fused  at  a 
very  high  temperature,  with  ten  times  its  quantity  of  sodium  car- 
bonate, sodium  aluminate  is  formed,  which  is  soluble  in  water 
(R.  RICHTER).  Placed  upon  moist  red  litmus-paper,  pure  alumina 
does  not  change  the  color  to  blue. 

t'OMFOSITK  >X. 

A12 55-00  53-40 

O3 48-00  46-60 


10?,.  oo  100-00 

c.  If  to  the  solution  of  a  salt  of  aluminium,  sodium  carbonate 
or  ammonium  carbonate  be  added,  till  the  resulting  precipitate  only 
just  redissolves  on  stirring,  and  then  sodium  acetate  or  ammonium 
acetate  poured  in  in  abundance  and  the  mixture  boiled  some  time, 
the  aluminium  is  precipitated  almost  completely  as  basic  acetate  in 
the  form  of  translucent  nocks,  so  that  if  the  filtrate  be  boiled  with 
ammonium   chloride   and   ammonia,  only   unweighable  traces   of 
aluminium  hydroxide  separate.     If  the  quantity  of  sodium  acetate 
employed  be  too  small,  the  precipitate  appears  more  granular,  the 
filtrate  would  then  contain  a  larger  amount  of  aluminium.     The 
precipitate  cannot  be  very  conveniently  filtered  and  washed.     In 
washing  it  is  best  to  use  boiling  water,  containing  a  little  sodium 
acetate  or  ammonium  acetate.     The  precipitate  is  readily  soluble 
in  hydrochloric  acid. 

d.  If,  instead  of  the  acetates  mentioned  in  <?,  the  corresponding 
formates   be   used,   a   flocculent  voluminous   precipitate  of   basic 
aluminium  formate  is  obtained,  which  may  be  very  readily  washed 
(FE.  SCHULZE*). 

§  f  6. 

2.  CHROMIUM. 

Chromium  is  usually  precipitated  as  CHROMIC  HYDROXIDE,  and 
always  weighed  as  chromic  oxide. 

a.  ( 'Irnniir  Jti/ilroxide  recently  precipitated  from  a  green  solu- 
tion, is  greenish-gray,  gelatinous,  insoluble  in  water:  it  dissolves 
readily,  in  the  cold,  in  solutions  of  potassa  or  soda,  to  a  dark  green 
fluid ;  it  dissolves  also  in  the  cold,  but  rather  sparingly,  in  solution 

*  Chem.  Centralbl.  1861,  3. 


152  FOUMS.  [§  77. 

of  ammonia,  to  a  light  violet  red  fluid.  In  acids  it  dissolves 
readily',  with  a  dark  green  color.  Presence  of  ammonium  chloride 
exercises  no  influence  upon  the  solubility  of  the  hydroxide  in 
ammonia.  Boiling  effects  the  complete  separation  of  the  hydroxide 
from  its  solutions  in  potassa,  or  ammonia  (Expt.  No.  41).  The 
dried  hydroxide  is  a  greenish-blue  powder  ;  it  is  converted  into 
oxide  with  loss  of  water  at  a  gentle  red  heat. 

1).  CHROMIC  OXIDE,  produced  by  heating  the  hydroxide  to  dull 
redness,  is  a  dark  green  powder ;  upon  the  application  of  a  higher 
degree  of  heat,  it  assumes  a  lighter  tint,  but  surfers  no  diminution 
of  weight ;  the  transition  from  the  darker  to  the  lighter  tint  is 
marked  by  a  vivid  incandescence  of  the  powder.  The  feebly 
ignited  oxide  is  difficultly  soluble  in  hydrochloric  acid,  and  the 
strongly  ignited  oxide  is  altogether  insoluble  in  that  acid.  It 
remains  unaltered  when  ignited  with  ammonium  chloride,  or  in 
a  current  of  hydrogen.  By  fusion  with  sodium  carbonate  and 
potassium  nitrate,  potassium  chromate  is  formed. 

COMPOSITION. 

Cr8     ....     104-96  68-62 

O3      ....       48-00  31-38 


152-96  100-00 

BASIC  RADICALS  OF  THE  FOURTH  GROUP. 

§•77- 
1.  ZINC. 

Zinc  is  weighed  in  the  form  of  OXIDE  or  SULPHIDE  ;  it  is  precipi- 
tated aS  BASIC  CARBONATE,  Ol'  as  SULPHIDE. 

a.  Basic  zinc  carbonate,  recently  precipitated,  is  white,  floccu- 
lent,  nearly  insoluble  in  water — (one  part  requiring  44600  parts, 
Expt.  ]STo.  42) — but  readily  soluble  in  potassa,  soda,  ammonia,  am- 
monium carbonate,  and  acids.  The  solutions  in  soda  or  potassa,  if 
concentrated,  are  not  altered  by  boiling ;  but  if  dilute,  nearly  all 
the  zinc  present  is  thrown  down  as  a  white  precipitate.  From  the 
solutions  in  ammonia  and  ammonium  carbonate,  especially  if  they 
are  dilute,  zinc  is  likewise  separated  upon  boiling.  When  a  neutral 
solution  of  zinc  is  precipitated  with  sodium  carbonate  or  potassium 
carbonate,  carbonic  acid  is  set  free,  since  the  precipitate  formed  is  not 


§  77.]  BASES    OF    (iKOfP    IV.  153 

ZnCO3,  but  consists  of  a  compound  of  zinc  hydroxide,  with  normal 
carbonate  in  proportions  varying  according  to  the  concentration  of 
the  solution,  and  to  the  mode  of  precipitation.  Owing  to  the 
presence  and  action  of  this  carbonic  acid,  part  of  the  zinc  remains 
in  solution ;  if  filtered  cold,  therefore,  the  nitrate  gives  a  precipi- 
tate with  ammonium  sulphide.  But  if  the  solution  is  precipitated 
boiling,  and  kept  at  that  temperature  for  some  time,  the  precipi- 
tation of  the  zinc  is  complete  to  the  extent  that  the  filtrate  is  not 
rendered  turbid  by  ammonium  sulphide ;  still,  if  the  filtrate,  mixed 
with  ammonium  sulphide,  be  allowed  to  stand  at  rest  for  many 
hours,  minute  and  almost  unweighable  flakes  of  zinc  sulphide  will 
separate  from  the  fluid.  The  precipitate  of  zinc  carbonate. 
obtained  in  the  manner  just  described,  may  be  completely  freed 
from  all  admixture  of  alkali  by  washing  with  hot  water.  If 
ammonium  salts  be  present,  the  precipitation  is  not  complete  till 
every  trace  of  ammonia  is  expelled.  If  the  solution  of  a  zinc  salt 
is  mixed  with  potassium  or  sodium  carbonate  in  excess,  the  mix- 
ture evaporated  to  dryness,  at  a  gentle  heat,  and  the  residue 
treated  with  cold  water,  a  perceptible  proportion  of  the  zinc  is 
obtained  in  solution  as  double  carbonate  of  zinc  and  potassium  or 
sodium;  but  if  the  mixture  is  evaporated  to  dryness,  at  a  boiling- 
heat,  and  the  residue  treated  with  hot  water,  the  whole  of  the 
zinc,  with  the  exception  of  an  extremely  minute  proportion,  as  we 
have  already  had  occasion  to  observe,  is  obtained  as  zinc  carbonate. 
The  dried  basic  zinc  carbonate  is  a  brilliant,  white,  loose  powder;, 
exposure  to  a  red  heat  converts  it  into  oxide. 

b.  Zinc  oxide,  produced  from  the  carbonate  by  ignition,  is  a 
white  light  powder,  with  a  slightly  yellow  tint.  When  heated,  it 
acquires  a  yellow  color,  which  disappears  again  on  cooling.  Upon 
ignition  with  charcoal,  carbon  monoxide  and  zinc  fumes  escape. 
By  igniting  in  a  rapid  current  of  hydrogen,  metallic  zinc  is  pro- 
duced; whilst  by  igniting  in  a  feeble  current  of  hydrogeiir 
crystallized  zinc  oxide  is  obtained  (Si.  CLAIRE  DEVILLE).  In  the 
latter  case,  too,  a  portion  of  the  metal  is  reduced  and  volatilized- 
Zinc  oxide  is  insoluble  in  water.  Placed  on  moist  turmeric  paper, 
it  does  not  change  the  color  to  brown.  In  acids,  zinc  oxide  dis- 
solves readily  and  without  evolution  of  gas.  Ignited  with  ammo- 
nium chloride,  fused  zinc  chloride  is  produced  which  volatilizes 
with  very  great  difficulty  if  the  air  is  excluded :  but  readily  and 
completely,  with  free  access  of  air,  and  with  ammonium  chloride; 


154  FORMS.  [§  77. 

fumes.  Mixed  with  a  sufficiency  of  powdered  sulphur  and  ignited 
in  a  stream  of  hydrogen,  the  corresponding  amount  of  sulphide  is 
obtained  (II.  ROSE). 


COMPOSITION. 


Zn 65-06  80-26 

O  16-00  19-74 


81-06  100-00 

c.  Zinc  sulphide,  recently  precipitated,  is  a  white,  loose  hydrate. 
The  following  facts  should  here  be  mentioned  with  regard  to  its 
precipitation.*  Colorless  ammonium  sulphide  precipitates  dilute 
solutions  of  zinc,  but  only  slowly ;  yellow  ammonium  sulphide 
does  not  precipitate  dilute  solutions  of  zinc  (1  :  5000)  at  all.  Am- 
monium chloride  favors  the  precipitation  considerably.  Free 
ammonia  acts  so  as  to  keep  the  precipitate  somewhat  longer  in 
suspension,  otherwise  it  exerts  no  injurious  influence.  If  the  con- 
ditions which  I  shall  lay  down  are  strictly  observed,  zinc  may  be 
precipitated  by  ammonium  sulphide  from  a  solution  containing 
only  yoiriroiro"-  Hyd  rated  zinc  sulphide  on  account  of  its  slimy 
nature  easily  stops  up  the  pores  of  the  filter,  and  cannot  therefore 
/be  washed  without  difficulty  on  a  filter.  The  washing  is  best 
performed  by  using  water  containing  ammonium  sulphide,  and 
continually  diminished  quantities  of  ammonium  chloride  (at  last 
none)  (see  Expt.  ~No.  43).  The  hydrate  is  insoluble  in  water,  in 
caustic  alkalies,  alkali  carbonates,  and  the  monosulphides  of  the 
alkali  metals.  It  dissolves  readily  and  completely  in  hydrochloric 
and  in  nitric,  but  only  very  sparingly  in  acetic  acid.  When  dried, 
the  precipitated  zinc  sulphide  is  a  white  powder  ;  when  air-dried 
its  composition  is  3ZnS  +  2II2O  ;  dried  at  100°,  2ZnS  -f  H2()  ; 
at  150°,  4ZnS  -f  ILO  (A.  SouoHAYf).  On  ignition  it  loses  the 
whole  of  its  water.  During  the  latter  process  some  hydrogen 
sulphide  escapes,  and  the  residue  contains  some  oxide.  By  roast- 
ing in  the  air,  and  intense  ignition,  small  quantities  of  zinc 
sulphide  may  be  readily  converted  into  the  oxide.  On  igniting 
the  dried  zinc  sulphide,  mixed  with  powdered  sulphur,  in  a  stream 
of  hydrogen,  the  pure  anhydrous  sulphide  is  obtained  (II.  ROSE). 
The  latter  suffers  no  loss  of  weight  worth  mentioning  by  ignition 
for  five  minutes  over  the  gas  blowpipe ;  but  if  such  ignition  is 

*  Jour.  f.  pnikt.  Chem.  82,  263.  f  Zeitschr.  f.  anal.  Chem.  7,  78. 


§  78.]  BASES    OF    GROUP    IV.  155 

very   protracted  the  loss   of   weight    becomes   considerable    (AL. 


COMPOSITION. 


Zn  .....     65-06  67-03 

S  32-00  32-97 


97-06         -   100-00 

§  T8. 

2.  MANGANESE. 
Manganese  is  weighed  either  as  PROTOSESQTJTOXIDE  (MANGANOSO- 

MANGANIC     OXIDE),    as     SULPHIDE,    aS     MANGANOUS      SULPHATE,    Or     OS 

PYROPHOSPHATE.    With  the  view  of  converting  it  into  these  forms, 
it  is  precipitated  as  MANGANOUS  CARBONATE,  MANGANOUS  HYDROX 

IDE,  MANGANESE    DIOXIDE,  Or  AMMONIUM    MANGANESE    PHOSPHATE. 

a.  Manganese  carbonate,  recently  precipitated,  is  white,  floccu- 
lent,  nearly  insoluble  in  pure  water,  but  somewhat  more  soluble  in 
water  impregnated  with  carbonic  acid.  Presence  of  sodium  car- 
bonate or  potassium  carbonate  does  not  increase  its  solubility. 
Recently  precipitated  manganese  carbonate  dissolves  pretty  readily 
in  ammonium  chloride:  it  is  owing  to  this  property  that  a  solution 
of  manganese  cannot  be  completely  precipitated  by  potassium  or 
sodium  carbonate,  in  presence  of  ammonium  chloride  (or  any  other 
ammonium  salt),  until  the  latter  is  completely  decomposed.  If 
the  precipitate,  while  still  moist,  is  exposed  to  the  air,  or  washed 
with  water  impregnated  with  air,  especially  if  it  is  in  contact  with 
alkali  carbonate,  it  slowly  assumes  a  dirty  brownish- white  color,  part 
of  it  becoming  converted  into  hydrated  protosesquioxide.  Even 
long-continued  washing  will  not  remove  the  last  traces  of  alkali 
salt  from  the  precipitate.  The  wash-water  often  comes  through 
turbid.  If  the  filtrate  and  wash -water  are  evaporated  to  dry  ness 
and  the  residue  is  treated  with  boiling  water,  the  small  traces  of 
manganous  carbonate  which  were  partly  dissolved  and  partly  sus- 
pended will  remain  behind  in  the  form  of  hydrated  protosesqui- 
oxide. Dried  by  pressure  the  precipitate  is  white,  and  consists  of 
MnCO3  +  H,O  ;  dried  in  a  vacuum  it  consists  of  2(MnCO3)  +  H2O 
(E.  PRiORf)  ;  when  dried  with  free  access  of  air,  the  powder  is  of 
a  dirty-white  color.  When  strongly  heated  with  access  of  air, 


*  Zeitschr.  f.  anal.  Chem.  4,  421.  f  lb.  8,  428. 


156  FORMS.  [§  78. 

this  powder  first  turns  black,  and  changes  subsequently  to  brown 
protosesquioxide  of  manganese.  However,  this  conversion  takes 
some  time,  and  must  never  be  held  to  be  completed  until  two 
weighings,  between  which  the  precipitate  has  been  ignited  again 
with  free  access  of  air,  give  perfectly  corresponding  results.  On 
igniting  the  manganous  carbonate,  mixed  with  powdered  sulphur, 
in  a  stream  of  hydrogen,  manganese  sulphide  is  obtained  (H.  HOSE). 

t>.  Manganous  hydroxide  recently  thrown  down  forms  a 
white,  flocculent  precipitate,  barely  soluble  in  water  and  alkalies, 
but  soluble  in  ammonium  chloride  ;  it  immediately  absorbs  oxygen 
from  the  air,  and  turns  brown,  owing  to  the  formation  of  hydrated 
protosesquioxide.  On  drying  it  in  the  air,  a  brown  powrder  is 
obtained  which,  when  heated  to  intense  redness,  with  free  access 
of  air,  is  converted  into  protosesquioxide,  and  on  ignition  with 
sulphur,  in  a  stream  of  hydrogen,  is  converted  into  sulphide. 

c.  Protosesquioxide  of  manganese^  artificially  produced,  is  a 
brown  powder.  All  the  oxides  of  manganese  are  finally  converted 
into  this  by  strong  ignition  in  the  air.  Each  time  it  is  heated  it 
assumes  a  darker  color,  but  its  weight  remains  unaltered.  It  is 
insoluble  in  water,  and  does  not  alter  vegetable  colors.  If  ignited 
with  ammonium  chloride,  it  is  converted  into  the  manganous 
chloride.  When  heated  with  concentrated  hydrochloric  acid,  it 
dissolves  to  chloride  with  evolution  of  chlorine  (Mn3O4  -|-  8IIC1  — 
3MnCl2  +  2C1  -f-  4H2O).  On  ignition  with  sulphur  in  a  stream 
of  hydrogen  it  is  converted  into  sulphide  (H.  ROSE).  On  ignition 
in  oxygen  it  is  converted  into  manganic  oxide  (SCHNEIDER).  On 
ignition  in  hydrogen  it  is  converted  into  manganous  oxide. 

COMPOSITION. 

Mn3    ....     165-00  72-05 

O4 64-00  27-95 


229-00  100-00 

d.  Manganese  dioxide  is  occasionally  produced  in  analysis  by 
exposing  a  concentrated  solution  of  manganous  nitrate  to  a 
gradually  increased  temperature.  At  140°  brown  flakes  separate, 
at  155°  much  nitrous  acid  is  disengaged,  and  the  whole  of  the 
manganese  separates  as  anhydrous  dioxide.  It  is  brownish-black, 
and  is  deposited  on  the  sides  of  the  vessel,  with  metallic  lustre.  It 
is  insoluble  in  weak  nitric  acid,  but  dissolves  to  a  small  amount  in 


§  78.]  BASES    OF    GROUP    IV.  IT)? 

hot  and  concentrated  nitric  acid  (DEVILLE).  In  hydrochloric  acid 
it  dissolves  with  evolution  of  chlorine,  in  concentrated  sulphuric 
acid  with  liberation  of  oxygen.  The  dioxide  is  also  sometimes 
obtained  in  the  hydrated  condition  in  analytical  separations,  thus 
when  we  precipitate  a  solution  of  a  mangaiious  salt  with  sodium 
hypochlorite,  or,  after  addition  of  sodium  acetate,  with  bromine  or 
chlorine  in  the  heat.  The  brownish-black  flocculent  precipitate 
thus  obtained,  contains  alkali,  from  whicli  it  cannot  be  well  freed 
by  washing.  ' 

e.  Manganese  sulphide,  prepared  in  the  wet  way,  generally 
forms  a  flesh-colored  precipitate.  I  must  make  a  few  remarks 
with  reference  to  its  precipitation.*  This  is  effected  but  incom- 
pletely if  we  add  to  a  pure  manganous  solution  only  ammonium 
sulphide,  no  matter  whether  it  be  colorless  or  yellow,  while  it  is 
perfectly  effected  if  ammonium  chloride  be  used  in  addition.  A 
large  quantity  even  of  ammonium  chloride  does  not  impede  the 
precipitation.  Ammonia  in  small  quantity  is  not  injurious,  but  in 
large  quantity  it  interferes  with  complete  precipitation,  especially 
in  the  presence  of  ammonium  polysulphide  (A.  CLASSEN-)-).  In  all 
cases  we  must  allow  to  stand  at  least  24  hours,  and  with  very 
dilute  solutions  48  hours,  before  filtering.  Colorless  or  slightly 
yellow  ammonium  sulphide  is  the  most  appropriate  precipitant. 
In  the  presence  of  ammonium  chloride  even  a  large  excess  of 
ammonium  sulphide  is  uninjurious.  If  the  precipitation  is  con- 
ducted as  directed,  the  manganese  can  be  precipitated  from  solu- 
tions which  contain  an  amount  equivalent  to  only  ^^Wo  °^  tne 
manganous  oxide.  If  the  flesh-colored  hydrated  sulphide  remains 
some  time  under  the  fluid,  from  which  it  was  precipitated,  it 
sometimes  becomes  converted  into  the  green  anhydrous  sulphide.:): 
This  conversion  is  more  likely  to  take  place  when  a  large  excess  of 
ammonium  sulphide  has  been  used;  heating  favors  it,  ammonium 
chloride  hinders  it.  The  conversion  is  occasionally  rapid.  The 
green  sulphide  thus  obtained  consists  of  eight-sided  tables  dis- 
tinctly visible  under  the  microscope  (F.  MUCK§).  In  acMs  (hydro- 
chloric, sulphuric,  acetic,  (fee.)  the  hydrated  sulphide  dissolves  with 
evolution  of  hydrogen  sulphide.  If  the  precipitate,  while  still 
moist,  is  exposed  to  the  air,  or  washed  with  water  impregnated  with 
air,  it  changes  to  brown,  hydrated  protosesquioxide  of  manganese 

*  Journ.  f.  prakt.  Chem.  82,  265.  f  Zeitschr.  f.  anal.  Chem.  8,  370. 

\  Journ.  f.  prakt.  Chem.  82,  268.  ?  Zeitschr.  f.  Chem.  N.  F.  6,  6. 


158  FORMS.  [§  78. 

being  formed,  together  with  a  small  portion  of  manganous  sulphate. 
Hence  in  washing  the  hydrate  we  always  add  some  ammonium  sul- 
phide to  the  wash-water,  and  keep  the  filter  as  full  as  possible  with 
the  same.  We  guard  against  the  filtrate  running  through  turbid, 
by  adding  gradually  decreasing  quantities  of  ammonium  chloride  to 
the  wash-water  (at  last  none).  (Expt.  No.  44.)  On  igniting  the 
precipitate  mixed  with  sulphur  in  a  stream  of  hydrogen  the 
anhydrous  sulphide  remains.  If  we  have  gently  ignited  during 
this  process,  the  product  is '  light  green ;  if  we  have  strongly 
ignited,  it  is  dark  green  to  black.  Neither  the  green  nor  the 
black  sulphide  attracts  oxygen  or  water  quickly  from  the  air 
(H.  ROSE).  The  anhydrous  sulphide  is  also  readily  soluble  in 
dilute  acids. 

COMPOSITION. 

Mn       ....     55-00  63-22 

S  32-00  36-78 


87-00  100-00 

f.  Anhydrous  manganous  sulphate,  produced  by  exposing  the 
crystallized  salt  to  the  action  of  heat,  is  a  white,  friable  mass, 
readily  soluble  in  water.  It  resists  a  very  faint  red  heat  ;  but 
upon  exposure  to  a  more  intense  red  heat,  it  suffers  more  or  less 
complete  decomposition  —  oxygen,  sulphur  dioxide,  and  sulphur 
trioxide  being  evolved,  and  protosesquioxide  of  manganese  re- 
maining behind.  Ignited  with  sulphur  in  a  stream  of  hydrogen  it 
is  transformed  into  sulphide  (H.  ROSE). 

COMPOSITION. 
^O    ^°^    Mn         Mn°      '      •      71'°°  47'°2 

>u'  <  O  '  SO,  ,    .    .    80'00  52'98    • 


151-00  100-00 


g.  Ammonium  manganese  phosphate.  —  GIBBS*  says  that  this 
precipitate  is  insoluble  in  boiling  water,  but  I  have  not  found  this 
to  be  the  case.  My  results  are  that  1  part  dissolves  in  32092  parts 
of  cold  water,  in  20122  parts  boiling  water,  and  17755  parts  of 
water  containing  -^  of  ammonium  chloride.  It  has  the  formula 


*  SILLIM.  Amer.  Journ.  (ii.)  44,  216. 


,    ~i)    I  BASES    OF    GROUP   IV.  159 

7STII4MnPO4  +  II.,O.  It  presents  pale  pink  scales  of  pearly 
lustre,  which  sometimes  turn  reddish  on  the  filter.  On  ignition  it 
is  converted  into  manganese  pyrophosphate. 

//.  Mdnganese  pyro/phosphdie  is  the  white  residue  left  on  the 
ignition  of  the  preceding. 

COMPOSITION. 

/PO<0>Mn_2MnO  .142  50 

^PO<g>Mn~P<°>  _^ 

284  100 


§  T9. 
3.  NICKEL. 

Xickel  is  precipitated  as  HYDROXIDE,  and  as  SULPHIDE.  It  is 
weighed  in  the  form  of  NICKELOUS  OXIDE,  of  METALLIC  NICKEL,  or 
of  anhydrous  NICKELOUS  SULPHATE. 

a.  Nickelous    hydroxide    forms    an    apple-green    precipitate, 
almost   absolutely  insoluble  in  water.     When  precipitated  from  a 
solution  of  the  chloride  or  sulphate,  it  retains  some  of  the  acid 
even  after  long  washing  (TEICHMANN*).     It  is  also  very  difficult  to 
remove  the  last  traces  of  alkali.     It  dissolves  with  some  difficulty 
in   ammonia  and  ammonium  carbonate,  far  more  readily  in  the 
presence  of  an  ammonium  salt.     From  these  solutions  it  is  com- 
pletely precipitated  by  excess  of  potassa  or  soda ;  application  of 
heat  promotes  the  precipitation.     It  is  unalterable  in  the  air  ;  on 
ignition,  it  passes  into  nickelous  oxide. 

b.  Niehelous  oxide  is  a  dirty  grayish-green   powder.     When 
obtained  by  heating  the  nitrate  to  redness,  it  always  contains  some 
nickelic  oxide,  and  requires  very  strong  and  protracted  ignition  for 
conversion  into  the  pure  green  nickelous  oxide  (W.  J.  EUSSELL). 
It  is  insoluble  in  water,  but  readily  soluble  in  hydrochloric  acid. 
It  does  not  affect  vegetable  colors.     It  suffers   no  variation   of 
weight  upon  ignition  with  free  access  of  air.     Mixed  with  am- 
monium  chloride   and   ignited,  it   is   reduced   to  metallic  nickel 
(II.  "ROSE);  it  is  also  easily  reduced  by  ignition  in  hydrogen  or 
carbon  monoxide. 


*  Aunal.  d.  Chera.  u.  Pliarm.  156,  17. 


160  FORMS.  [§  '/£. 


COMPOSITION. 


M      ....     59  78- 6T 

O  16  21-33 


75  100-00 

c.  Metallic  nickel  obtained  by  the  reduction  of  nickelous  oxide 
with  hydrogen  has  the  form  of  a  gray  powder,  or  if  the^  heat  has 
been  very  strong,  and  it  has  melted,  it  is  lustrous  and  white  like 
silver.     It  is  unaltered  in   weight  by  ignition  in  hydrogen,  when 
ignited  in  the  air  it  is  superficially  oxidized.     It  is  attracted  by 
the  magnet.    It  is  dissolved  slowly  by  hydrochloric  acid  and  dilute 
.sulphuric  acid,  and  readily  by  moderately  strong  nitric  acid. 

d.  Anhydrous  nickelous  sulphate  obtained   by  evaporating  a 
solution  of  the  chloride,  nitrate,  &c.,  with  sulphuric  acid  is  yellow, 
soluble   in   water   to    a   green  fluid.     The  hydrous  salt  may  be 
rendered  anhydrous  without  loss  of  acid  by  cautious  heating  in  a 
platinum  dish,  but  at  low  redness  it  begins  to  blacken  at  the  edges 
and  loses  acid  (F.  GAIT  HE*). 

e.  Hydrated  nickelous   sulphide,  prepared    in    the  wet   way, 
forms  a  black  precipitate,  insoluble  in  water.     I  must  make  some 
observations  on  its  precipitation. f    In  order  to  precitate  the  nickel 
from  a  pure  solution  completely  and  with  ease,  ammonium  chloride 
must  be  present ;  it  is  not  enough  to  add  ammonium  sulphide 
alone.     A  large  quantity  even  of  ammonium  chloride  produces  no 
injurious  effect.     In  the  presence  of  free  ammonia,  on  the  con- 
trary, some  nickel  remains  in  solution.     In  this  case,  the  super- 
natant fluid   appears  brown.     As   precipitant,  colorless    or   ligl it- 
yellow  ammonium  sulphide  containing  no  free  ammonia  should  be 
used,  a  large  excess  must  be  avoided.     If  the  directions  given  are 
adhered  to — allowing  to  stand  48  hours — the  nickel  may  be  pre- 
cipitated by   means  of  ammonium  sulphide,   from  solutions  con- 
taining only  8~o-o^o-o  °^  ^e  oxide.     ^s  tne  precipitate  is  liable  to 
take  up  oxygen  from  the  air,  being  transformed  into  sulphate,  a 
little  ammonium  sulphide  is  mixed  with  the  wash-water,  to  which 
also  it  is  advisable  to   add  ammonium   chloride  (less  and  less — at 
last  none) ;  the  filter  should  be  kept  full'  (Expt.  'No.  45).     Brown 
filtrates,  containing  nickel  sulphide  in  solution,  may  be  freed  from 
the  latter  by  acidulation  with  acetic  acid,  and  boiling  some  time. 


*  Zeitschr.  f.  anal.  Chem.  4,  190.          f  Journ.  f.  prakt.  Chem.  82,  257. 


§80.]  BASES    OF   GROl'P    IV.  161 

The  sulphide  falls  down,  and  may  now  be  filtered  off.  It  is  very 
sparingly  soluble  in  concentrated  acetic  acid,  somewhat  more  soluble 
in  hydrochloric  acid.  It  is  more  readily  soluble  still  in  nitric  acid, 
but  its  best  solvent  is  nitro-hydrochloric  acid.  It  loses  its  water  upon 
the  application  of  a  red  heat ;  when  ignited  in  the  air,  it  is  trans- 
formed into  a  basic  compound  of  nickelous  oxide  with  sulphuric  acid. 
Mixed  with  sulphur  and  ignited  in  a  stream  of  hydrogen,  a  fused 
mass  remains,  of  pale  yellow  color  and  metallic  lustre.  This  consists 
of  Xi2S,  but  its  composition  is  not  perfectly  constant  (F.  GAUHE*). 
[Xickel  may  be  precipitated  as  a  sulphide,  dense  in  form,  easy 
to  wash,  and  not  readily  oxidizing  by  contact  with  air,  by  proceed- 
ing as  follows  :  To  the  solution,  which  should  be  concentrated  and 
contain  a  liberal  quantity  of  ammonium  salts,  add  ammonia  (if 
necessary)  to  alkaline  reaction,  then  acetic  acid  to  slight  acid  reac- 
tion, also  ammonium  or  sodium  acetate,  and  heat,  to  bolting. 
Transmit  H,S  gas  through  the  boiling  solution.  Since  much  free 
acetic  acid  prevents  complete  precipitation,  it  is  necessary  some- 
times when  much  nickel  is  present  to  partially  neutralize  once  or 
twice  the  acid  set  free  during  the  process.] 

Xickel  sulphide  may  be  converted  into  nickelous  sulphate  bv 
dissolving  in  nitric  acid  and  evaporating  with  sulphuric  acid. 

§  80. 
4.  COBALT. 

Cobalt  is  weighed  in  the  PURE  METALLIC  state,  or  as  COBALTOUS 
SULPHATE.  Besides  the  properties  of  these  substances,  we  have  to 
study  also  those  of  COBALTOUS  HYDROXIDE,  of  the  SULPHIDE,  and  of 

the  TRIPOTASSIUM    COBALTIC    NITRITE. 

a.  Cobaltous  hydroxide. — Upon  precipitating  a  solution  of  a 
cobaltous  salt  with  potassa,  a  blue  precipitate  (a  basic  salt)  is 
formed  at  first,  which,  upon  boiling  with  potassa  in  excess,  exclud- 
ed from  contact  of  air.  changes  to  light  red  cobaltous  hydroxide ; 
if,  on  the  contrary,  this  process  is  conducted  with  free  access  of 
air.  the  precipitate  becomes  discolored,  and  finally  black,  part  of 
the  cobaltous  hydroxide  being  converted  into  cobaltic  hydroxide. 
But  the  hydroxide  prepared  in  this  way,  retains  always  a  certain 
quantity  of  the  acid,  and,  even  after  the  most  thorough  washing 


Zeitschr.  f.  anal.  Chem.  4,  191. 


162  FORMS.  [§  80. 

with  hot  water,  also  a  small  amount  of  the  alkaline  precipitant. 
.The  latter,  however,  is  not  enough  to  spoil  the  accuracy  of  the 
results  (H.  ROSE,  F.  GATJIIE*).  Cobaltous  hydroxide  is  insoluble 
in  water,  and  also  in  dilute  potassa  ;  it  is  somewhat  soluble  in  very 
concentrated  potassa,  and  readily  in  ammonium  salts.  When  dried 
in  the  air,  it  absorbs  oxygen,  and  acquires  a  brownish  color.  By 
strong  ignition  it  is  converted  into  cobaltous  oxide  (even  if  some 
higher  oxide  had  formed  from  boiling  or  drying  in  the  air) ;  if 
cooled  with  exclusion  of  air,  as  in  a  current  of  carbon  dioxide, 
pure  light.brown  cobaltous  oxide  will  be  left ;  if  cooled,  on  the 
contrary,  with  access  of  air,  it  is  more  or  less  changed  to  black 
protosesquioxide  (cobaltoso-cobaltic  oxide)  (W.  J.  RUSSELL!).  By 
ignition  in  a  current  of  hydrogen,  metallic  cobalt  is  left,  from 
which  any  traces  of  alkali  may  now  be  almost  completely  removed 
by  boiling  water. 

I.  The  metallic  cobalt  obtained  according  to  a,  or  by  igniting 
the  chloride  or  the  protosesquioxide  (produced  by  igniting  the 
nitrate)  in  hydrogen  is  a  grayish-black  powder,  which  is  attracted 
by  the  magnet,  and  is  more  difficultly  fusible  than  gold.  If  the 
reduction  has  been  effected  at  a  faint  heat,  the  finely  divided  metal 
burns  in  the  air  to  protosesquioxide  of  cobalt,  which  is  not  the 
case  if  the  reduction  has  been  effected  at  an  intense  heat.  Cobalt 
does  not  decompose  water,  either  at  the  common  temperature, 
or  upon  ebullition — except  sulphuric  acid  be  present,  in  which 
case  decomposition  will  ensue.  Heated  with  concentrated  sul- 
phuric acid,  it  forms  cobaltous  sulphate,  with  evolution  of  sulphur 
dioxide.  In  nitric  acid  it  dissolves  readily  to  cobaltous  nitrate. 

c.  Cobalt  sulphide,  produced  in  the  wet  way,  forms  a  black 
precipitate,  insoluble  in  water,  alkalies,  and  alkali  sulphides.  With 
regard  to  its  precipitation,  £ — this  is  effected  but  slowly  and  im- 
perfectly by  ammonium  sulphide  alone ;  in  the  presence  of  am- 
monium chloride  however,  it  takes  place  quickly  and  completely. 
Free  ammonia  is  not  injurious  ;  it  is  all  one,  whether  colorless  or 
yellow  ammonium  sulphide  is  employed.  If  the  directions  given 
are  observed,  cobalt  may  be  precipitated  from  a  solution  contain- 
ing no  more  than  innAnnr  °f  *he  protoxide.  In  the  moist  con- 
dition, exposed  to  the  air,  it  oxidizes  to  sulphate.  In  washing  it, 
therefore,  water  containing  ammonium  sulphide  is  employed,  and 

*  Zeitschr.  f.  anal.  Chem.  4,  54.  f  Journ.  Chem.  Soc.  (2)  1,  51. 

•  \  Journ.  f.  prakt.  Chera.  82,  262. 


BASES    OF   GROUP    IV.  163 

the  filter  is  kept  full.  It  is  advisable  also  to  mix  a  little  ammo- 
nium chloride  with  the  wash-water,  but  its  quantity  should  be 
gradually  decreased,  and  the  last  water  used  must  contain  none. 
It  is  but  sparingly  soluble  in  acetic  acid  and  in  dilute  mineral 
acids,  more  readily  in  concentrated  mineral  acids,  and  most  readily 
in  warm  nitro-hydrochloric  acid.  Mixed  with  sulphur  and  ignited 
in  a  stream  of  hydrogen,  we  obtain  a  product  which  varies  in 
composition  according  to  the  temperature  employed.  The  residue 
is  therefore  not  suited  for  the  determination  of  cobalt  (H.  ROSE). 
Cobalt  can  be  precipitated  as  sulphide  completely  in  the  presence 
of  a  very  small  amount  of  free  acetic  acid  by  hydrogen  sulphide  in 
the  same  manner  as  nickel  (see  §  79,  e).  Cobalt  sulphide  may  be 
converted  into  cobaltous  sulphate  by  heating  in  the  air,  moistening 
with  nitric  acid,  evaporating  with  sulphuric  acid  and  igniting. 

d.  CqbciUous  sulphate  crystallizes,  in  combination  with  7  aq., 
slowly  in  oblique  rhombic  prisms  of  a  fine  red  color.  The  crystals 
yield  the  whole  of  the  water,  at  a  moderate  heat,  and  are  con- 
verted into  a  rose-colored  anhydrous  salt,  which  bears  the  applica- 
tion of  a  low  red  heat  without  losing  acid.  At  a  stronger  heat  the 
edges  become  black  and  some  sulphuric  acid  escapes  (F.  GAUHE*). 
It  dissolves  rather  difficultly  in  cold,  but  more  readily  in  hot  water. 

COMPOSITION. 

„  O  ^              CoO     .     .         .75          48-39 
°*  <  O  -  ~S03 80          51-61 


155         100-00 

e.  Tripotassiv.m  cobaltie  nitrite. — If  a  solution  of  a  cobalt  salt 
(not  too  dilute)  is  mixed  with  excess  of  potassa  and  then  with 
acetic  acid  till  the  precipitate  is  redissolved,  and  a  concentrated 
solution  of  potassium  nitrite  previously  acidified  with  acetic  acid  is 
added,  first  a  dirty,  brownish  precipitate  forms  which  gradually 
turns  yellow  and  crystalline,  especially  on  the  application  of  a 
gentle  heat  (X.  ~W.  FISCHER!).  The  composition  of  this  precipi- 
tate corresponds  to  the  formula  (KNO2)6Co3(!N"O2)6  +  aq.  x  (SADT- 
LER).  Dried  at  100°  its  composition  is  somewhat  variable  (STKO- 
MEYER,  EnmiAxx;}:).  It  is  decidedly  soluble  in  water,  less  in 
potassium  acetate  whether  neutral  or  acidified  with  acetic  acid, 

*  Zeitschr.  f.  anal.  Chem.  4,  55.  fPogg.  Ann.  72,  477. 

\  Journ.  f.  prakt.  Chem.  97,  385. 


164  FORMS.  [§    81. 

not  in  potassium  acetate  to  which  some  potassium  nitrite  has 
been  added,  not  in  potassium  nitrite,  nor  in  alcohol  of  80  per 
cent.  On  washing  with  water  or  solution  of  potassium  acetate, 
unless  potassium  nitrite  is  added,  nitric  oxide  is  constantly  evolved 
in  small  quantities.  It  is  decomposed  with  separation  of  brown 
cobaltic  hydroxide,  with  difficulty  by  solution  of  potassa,  with  ease 
by  soda  or  baryta.  On  being  moistened  with  sulphuric  acid  and 
ignited  (finally  with  addition'  of  ammonium  carbonate)  it  leaves 
2(CoSO4)  +  3(K2SO4),  but  there  is  a  difficulty  in  driving  off  all 
the  excess  of  acid  without  decomposing  the  cobaltous  sulphate. 
The  yellow  salt  is  soluble  in  hydrochloric  acid,  potassa  precipitates 
the  whole  of  the  cobalt  from  this  solution  as  hydroxide. 

§  81. 
5.  FERROUS  IRON  ;    and  6.   FERRIC  IRON. 

Iron  is  ifsually  weighed  in  the  form  of  FERRIC  OXIDE,  occasion- 
ally as  SULPHIDE.  We  have  to  study  also  the  FERRIC  HYDROXIDE, 

the  FERRIC  SUCCINATE,  the  FERRIC  ACETATE,  and  the  FERRIC  FORMATE. 

a.  Ferric  hydroxide,  recently  prepared,  is  a  reddish-brown 
precipitate,  insoluble  in  water,  in  dilute  alkalies,  and  in  ammonium 
salts,  but  readily  soluble  in  acids ;  it  shrinks  very  greatly  on 
drying.  When  dry,  it  presents  a  brown,  hard  mass,  with  shining 
•conchoidal  fracture.  If  the  precipitant  alkali  is  not  used  in  excess, 
the  precipitate  contains  basic  salt ;  on  the  other  hand,  if  the  alkali 
has  been  used  in  excess,  a  portion  of  it  is  invariably  carried  down 
in  combination  with  the  ferric  hydroxide, — on  which  account 
ammonia  alone  can  properly  be  used  in  analysis  for  this  purpose. 
Under  certain  circumstances,  for  instance,  by  protracted  heating  of 
a  solution  of  ferric  acetate  on  the  water-bath  (which  turns  the 
solution  from  blood-red  to  brick-red,  and  makes  it  appear  turbid 
by  reflected  light),  and  subsequent  addition  of  some  sulphuric  acid 
or  salt  of  an  alkali,  a  reddish-brown  hydrated  ferric  oxide  is  pro- 
duced, which  is  insoluble  in  cold  acids,  even  though  concentrated, 
and  is  not  attacked  even  by  boiling  nitric  acid  (L.  PEAN  DE  ST. 
GILLES*). 

Closely  allied  to  ferric  hydroxide  are  the  highly  basic  salts 
obtained  by  mixing  dilute  cold  solutions  of  ferric  salts,  best  ferric 
chloride,  with  much  ammonium  chloride,  cautiously  adding  am- 

*  Journ.  f.  prakt.  Chem.  66,  137. 


g  81.]  BASKS    OF    GROUP   IV.  165 

monimn  carbonate  till  the  fluid  on  standing  in  the  cold  instead  of 
becoming  clear  turns  more  turbid  if  anything,  and  then  boiling. 
The  precipitates,  thus  produced  in  the  fluid  which  still  retains  its 
acid  reaction,  contain  the  whole  of  the  iron  present  and  play  an 
important  part  in  analytical  separations.  They  should  be  washed 
with  boiling  water  containing  ammonium  chloride,  being  soluble  to 
a  slight  extent  in  pure  water.  They  are  not  suitable  for  ignition, 
as  ferric  chloride  might  occasionally  escape  from  them. 

I.  Ferric  hydroxide  is,  upon  ignition,  converted  into  ferric 
o.i'ide.  If  the  hydroxide  has  been  superficially  dried  only,  the 
violent  escape  of  steam  from  the  lumps  is  likely  to  occasion  loss ; 
but  if  it  has  been  dried  as  much  as  possible  by  suction  and  still 
remains  moist,  it  may  be  ignited  without  fear  of  loss.  Pure  ferric 
oxide,  when  placed  upon  moist  reddened  litmus-paper,  does  not 
change  the  color  to  blue.  It  dissolves  slowly  in  dilute,  but  more 
rapidly  in  concentrated  hydrochloric  acid ;  the  application  of  a 
moderate  degree  of  heat  effects  this  solution  more  readily  than 
boiling.  With  a  mixture  of  8  parts  concentrated  sulphuric  acid 
and  3  parts  water,  it  behaves  in  the  same  manner  as  alumina.  The 
weight  of  ferric  oxide  does  not  vary  upon  ignition  in  the  air; 
when  ignited  with  ammonium  chloride,  ferric  chloride  escapes. 
Ignition  with  charcoal,  in  a  closed  vessel,  reduces  it  more  or  less. 
Strongly  ignited  with  sulphur  in  a  stream  of  hydrogen,  it  is  trans- 
formed into  ferrous  sulphide. 

COMPOSITION. 

Fea 112  70-00 

O3 48  30-00 


160  100. on 

c.  Ferrous  sulphide,  produced  in  the  wet  way,  forms  a  black 
precipitate.  The  following  facts  are  to  be  noticed  with  regard 
to  its  precipitation.-)-  Ammonium  sulphide  used  alone,  whether 
colorless  or  yellow,  precipitates  pure  neutral  solutions  of  ferrous 
salts,  but  slowly  and  imperfectly.  Ammonium  chloride  acts  very 
favorably ;  a  large  excess  even  is  not  attended  with  inconvenience. 
Ammonia  has  no  injurious  action.  It  is  all  the  same  whether  the 
ammonium  sulphide  be  colorless  or  light  yellow.  If  the  direc- 


.,  82,  268. 


166  FORMS.  [§   81. 

tions  given  are  observed,  iron  may  be  precipitated  by  means  of 
ammonium  sulphide,  from  solutions  containing  only  TF^  ^-5-5-  of 
ferrous  oxide.  In  such  a  case,  however,  it  is  necessary  to  allow  to 
stand  forty-eight  hours.  Since  the  precipitate  rapidly  oxidizes  in 
contact  with  air,  ammonium  sulphide  is  to  be  added  to  the  wash- 
water,  and  the  filter  kept  full.  It  is  well  also  to  mix  a  little 
ammonium  chloride  with  the  wash-water,  but  the  quantity  should 
be  continually  reduced,  and  the  last  water  used  should  contain 
none.  In  mineral  acids,  even  when  very  dilute,  the  hydrated 
sulphide  dissolves  readily.  Mixed  with  sulphur,  and  strongly 
ignited  in  a  stream  of  hydrogen,  anhydrous  ferrous  sulphide  re- 
mains (H.  HOSE). 

COMPOSITION. 

Fe 56  63-64 

S  32  36-36 


88  100-00 

d.  When  a  neutral  solution  of  a  ferric  salt  is  mixed  with  a 
neutral  solution  of  an  alkali  succinate,  a  cinnamon-colored  precipi- 
tate of  a  brighter  or  darker  tint  of  a  basic  ferric  succinate  is 
formed,  succinic  acid  being  set  free.     The  free  succinic  acid  does 
not  exercise  any  perceptible  solvent  action  upon  the  precipitate  in 
a  cold  and  highly  dilute  solution,  but  it  redissolves  the  precipitate 
a  little  more  readily  in  a  warm  solution.     The  precipitate  must 
therefore  be  filtered  cold,  if  we  want  to  guard  against  re-solution. 
Formerly  the  precipitate  was  erroneously  supposed  to  consist  of  a 
normal  salt,  decomposable   by  hot  water  into  an  insoluble  basic 
and  a  soluble  acid  compound.    Basic  ferric  succinate  is  insoluble  in 
cold,  and  but  sparingly  soluble  in  hot  water.     It  dissolves  readily 
in  mineral  acids.     Ammonia,  especially  if  w^arm,  deprives  it  of  the 
greater  portion  of  its  acid,  leaving  compounds  which  are  highly 
basic  ferric  succiiiates  (DOPPING). 

e.  If  to  a  solution  of  a  ferric  salt,  sodium  carbonate  be  added 
in   the   cold,   till   the   fluid   contains   no  more  free  acid,  and  in 
consequence  of  the  formation  of  basic  salt  has  become  deep  red, 
but  remains  still  perfectly  clear,  and  then  sodium  acetate  be  poured 
in  and  the  mixture  boiled,  the  whole  of  the  iron  will  be  precipi- 
tated as  basic  ferric  acetate. 

f.  Instead  of  the  sodium  or  ammonium  acetate  used  in  <?,  the  cor- 


§82.]  BASKS    OF    (iROCP    V.  167 

responding  formates  may  be  used.     The  basic  ferric  formate  here 
obtained  is  more  easily  washed  than  the  basic  acetate  f¥.  SCHULZE*). 

BASIC   RADICALS   OF    THE   FIFTH   GROUP. 

.*  82. 
1.  SILVER. 

Silver  may  be  weighed  in  the  METALLIC  state,  as  CHLORIDE,  SUL- 
PHIDE, or  CYANIDE. 

a.  Metallic  xtlver,  obtained  by  the  ignition  of  salts  of  silver 
with  organic  acids,  &c.,  is  a  loose,  white,  glittering  mass  of  metallic 
lustre ;  but,  when  obtained  by  reducing  silver  chloride,  &c.,  in  the 
wet  way,  by  zinc,  it  is  a  dull- gray  powder.  It  fuses  at  about  1000°. 
Its  weight  is  not  altered  by  moderate  ignition.  It  may,  however, 
be  distilled  by  the  heat  of  the  oxy hydrogen  flame  (CHRisTOMAjsrosf). 
It  dissolves  readily  and  completely  in  dilute  nitric  acid. 

1}.  Silver  chlwide,  recently  precipitated,  is  white  and  curdy. 
On  shaking,  the  large  spongy  flocks  combine  with  the  smaller 
particles,  so  that  the  fluid  becomes  perfectly  clear.  This  result  is, 
however,  only  satisfactorily  effected  when  the  flocks  have  been 
recently  precipitated  in  presence  of  excess  of  silver  solution  (com- 
pare G.  J.  MULDER:}:).  Silver  chloride  is  in  a  very  high  degree 
insoluble  in  water,  and  in  dilute  nitric  acid;  strong  nitric  acid,  on 
the  contrary,  does  dissolve  a  trace.  Hydrochloric  acid,  especially 
if  concentrated  and  boiling,  dissolves  it  very  perceptibly.  Accord- 
ing to  PIERRE,  1  part  of  silver  chloride  requires  for  solution  200 
parts  of  strong  hydrochloric  acid  and  600  parts  of  a  dilute  acid, 
composed  of  1  part  strong  acid  and  2  parts  water.  On  sufficiently 
diluting  such  a  solution  with  cold  water  the  silver  chloride  is  pre- 
cipitated so  completely  that  the  filtrate  is  not  colored  by  "hydrogen 
sulphide.  Silver  chloride  is  insoluble,  or  very  nearly  so,  in  con- 
centrated sulphuric  acid ;  in  the  dilute  acid  it  is  as  insoluble  as  in 
water.  In  a  solution  of  tartaric  acid  silver  chloride  dissolves  per- 
ceptibly on  warming ;  on  cooling,  however,  the  solution  deposits 
the  whole,  or,  at  all  events,  the  greater  part  of  it.  Aqueous  solu- 
tions of  chlorides  (of  sodium,  potassium,  ammonium,  calcium,  zinc, 


*  Chem.  Centralblatt,  1861,  3.  t  Zeitschr.  f.  anal.  Chem.  7,  299. 

\  Die  Silberprobirmethode,  translated  into  German  by  D.  Cbr.  Grimm,  pp. 
19  and  311.     Leipzig  :  J.  J.  Weber.     1859  . 


168  FORMS.  [§  82. 

&G.)  all  dissolve  appreciable  quantities  of  silver  chloride,  especially 
if  they  are  hot  and  concentrated.  On  sufficient  dilution  with  cold 
water  the  dissolved  portion  separates  so  completely  that  the  filtrate 
is  not  colored  by  hydrogen  sulphide.  The  solutions  of  alkali  and 
alkali-earth  nitrates  also  dissolve  a  little  silver  chloride.  The  solu- 
bility in  the  cold  is  trifling ;  in  the  heat,  on  the  contrary,  it  is  very 
perceptible.  A  strong  solution  of  silver  nitrate  dissolves  it  slightly, 
especially  in  the  heat ;  but  I  have  found  it  insoluble  in  a  moder- 
ately dilute  cold  solution  of  lead  nitrate.  The  action  of  mercuric 
salts  upon  it  is  remarkable.  When  well  washed  and  treated  with  a 
very  dilute  solution  of  mercuric  chloride  it  becomes  white  if  pre- 
viously a  little  blackened  by  light,  is  easily  diffused  in  the  fluid, 
and  is  but  tardily  deposited.  This  depends  upon  the  mercuric  salt 
being  taken  up  ;  if  the  silver  salt  is  washed  the  mercuric  salt  will 
be  removed.  Mercuric  nitrate  acts  in  a  similar  way,  but  a  certain 
quantity  of  silver  passes  at  the  same  time  into  solution.  Silver 
chloride  is  much  more  difficultly  dissolved  by  mercuric  acetate  than 
by  mercuric  nitrate ;  therefore,  if  you  have  a  solution  of  mercuric 
nitrate  containing  silver  chloride,  if  the  mercuric  salt  is  not  present 
in  enormous  quantity,  the  silver  may  be  almost  absolutely  thrown 
down  by  addition  of  an  alkali  acetate  (H.  DEBRAY*).  Solutions 
of  potash  and  soda  decompose  silver  chloride,  even  at  the  ordinary 
temperature,  more  readily  on  boiling ;  silver  oxide  separates,  and 
chloride  of  the  alkali  metal  is  formed.  Solution  of  sodium  or 
potassium  carbonate  decomposes  silver  chloride  only  very  imper- 
fectly even  on  boiling ;  after  long  boiling  decided  traces  of  chlorine 
are  found  in  the  filtrate.  Silver  chloride  dissolves  readily  in  aque- 
ous ammonia,  and  also  in  the  solution  of  potassium  cyanide  and 
that  of  sodium  thiosulphate.  According  to  WALLACE  and  LAMONxf 
1  part'of  silver  chloride  dissolves  in  12-88  parts  of.  strong  aqueous 
ammonia  of  '89  sp.  gr.  Under  the  influence  of  light  silver  chlo- 
ride soon  changes  to  violet,  finally  black,  losing  chlorine,  and  pass- 
ing partly  into  AgaCl.  The  change  is  quite  superficial,  but  the 
loss  of  weight  resulting  is  very  appreciable  (MULDER,  op.  cit.,  p. 
21).  If  silver  chloride  that  has  become  violet  or  black  from  the 
influence  of  light  be  treated  with  aqueous  ammonia,  it  dissolves 
with  separation  of  a  very  small  quantity  of  metallic  silver,  Ag2Cl 
gives  AgCl  and  Ag  (WITTSTEIN).  On  long  contact  (say  for  24 


*  Zeitschr.  f.  Chem.  13,  348.  f  Chem.  Gaz.  1859,  137. 


§  82.]  BASES    OF    OROUP    V.  169 

hours)  with  water,  especially  of  75°,  silver  chloride,  although 
removed  from  the  influence  of  light,  becomes  gray,  and,  it  appears, 
decomposed ;  the  precipitate  is  found  to  contain  silver  oxide,  and 
the  water  hydrochloric  acid  (MULDEK).  On  digestion  with  excess 
of  solution  of  potassium  bromide  or  iodide,  silver  chloride  is  com- 
pletely transformed  into  silver  bromide  or  iodide,  as  the  case  may 
be  (FIELD*).  On  drying,  silver  chloride  becomes  pulverulent ;  on 
heating  it  turns  yellow ;  at  260°  it  fuses  to  a  transparent  yellow 
fluid;  at  a  very  high  heat  it  volatilizes  without  decomposition. 
On  cooling  after  fusion  it  presents  a  colorless  or  pale  yellowish 
mass.  Fused  in  chlorine  gas,  it  absorbs  some  chlorine  ;  on  cooling, 
this  escapes,  but  not  completely.  If  it  is  to  be  completely  expelled, 
and,  in  very  delicate  experiments  this  must  be  done,  we  pass  car- 
bon dioxide  before  allowing  to  cool  (STAS  f).  Ignition  with  char- 
coal fails  to  effect  its  reduction  to  the  metallic  state  ;  but  it  may 
be  readily  so  reduced  in  a  current  of  hydrogen,  carburetted  hydro- 
gen, or  carbon  monoxide. 

COMPOSITION. 

Ag 107-93  75.27 

01  35-46  24-73 


143-39  100-00 

c.  Silver  sulphide,  prepared  in  the  wet  way,  is  a  black  precipi- 
tate, insoluble  in  water,  dilute  acids,  alkalies,  and  alkali  sulphides. 
It  is  unalterable  in  the  air ;  after  being  allowed  to  subside,  it  is 
filtered  and  washed  with  ease,  and  may  be  dried  at  100°  without 
decomposition.  It  dissolves  in  concentrated  nitric  acid,  with 
separation  of  sulphur.  Solution  of  potassium  cyanide  dissolves 
it  with  difficulty,  if  it  has  been  precipitated  from  a  very  dilute 
solution  with  less  difficulty ;  the  quantity  of  potassium  cyanide, 
too,  has  great  influence  on  the  effect.  For  instance,  if  silver  cya- 
nide, is  dissolved  in  a  bare  sufficiency  of  potassium  cyanide  and 
hydrogen  sulphide,  or  ammonium  sulphide  is  added,  silver  sulphide 
is  thrown  down ;  if,  on  the  other  hand,  a  large  excess  of  potassium 


*  Quart.  Journ.  Chem.  Soc.  10,  234. 

f  Recherches  sur  less  rapports  reciproques  des  poids  .atomiques,  p.  37. 
Bruxelles,  1860.  The  loss  of  weight  which  about  100  grm.  chloride  of  silver 
suffered,  by  the  expulsion  of  the  absorbed  chlorine,  was  from  7  to  13  mgrm. 


170  FORMS.  [§  83. 

cyanide  is  present,  no  precipitate  will  be  produced.  If  silver 
sulphide  is  dissolved  in  a  concentrated  solution  of  potassium  cya- 
nide, it  will  generally  separate  at  once  on  addition  of  much  water 
(BECHAMP*).  Ignited  in  a  current  of  hydrogen,  it  passes  readily 
and  completely  into  the  metallic  state  (H.  ROSE). 

COMPOSITION. 

Ag2 215-86  87-09 

S  32-00  12-91 


- 86  100-00 

d.  Silver  cyanide,  recently  thrown  down,  forms  a  white  curdy 
precipitate  insoluble  in  water  and  dilute  nitric  acid,  soluble  in 
potassium  cyanide  arid  also  in  ammonia ;  exposure  to  light  fails 
to  impart  the  slightest  tinge  of  black  to  it ;  it  may  be  dried  at  100° 
without  decomposition.  Upon  ignition,  it  is  decomposed  into 
cyanogen,  which  escapes,  and  metallic  silver,  which  remains,  mixed 
with  a  little  paracyanide  of  silver.  By  boiling  with  a  mixture  of 
equal  parts  of  sulphuric  acid  and  water,  it  is,  according  to  GLASS- 
FORD  and  NAPIER,  dissolved  to  silver  sulphate,  with  liberation  of 
hydrocyanic  acid. 

COMPOSITION. 

Ag 10T-93  80-56 

ON  26-04  19-44 


133-97  100-00 

§83. 
2.  LEAD. 

Lead  is  weighed  as  OXIDE,  SULPHATE,  CHROMATE,  CHLORIDE,  and 
SULPHIDE.  Besides  these  compounds,  we  have  also  to  study  the 
CARBONATE  and  the  OXALATE. 

a.  Normal  lead  carbonate  forms  a  heavy,  white,  pulverulent 
precipitate.  It  is  but  very  slightly  soluble  in  perfectly  pure  (boiled) 
water,  one  part  requiring  50550  parts  (see  Expt.  No.  47,  a) ;  but 
it  dissolves  somewhat  more  readily  in  water  containing  ammonia 
and  ammonium  salts  (comp.  Expt.  No.  47,  b  and  c\  and  also  in 

*  Journ.  f.  prakt.  Chem.  60,  64. 


g  83.]  BASES    OF    GROUP   V.  171 

water  impregnated  with  carbonic  acid.  It  loses  its  carbonic  acid 
when  ignited. 

1).  Ltcul  oxalate  is  a  white  powder,  very  sparingly  soluble  in 
water.  The  presence  of  ammonium  salts  slightly  increases  its  solu- 
bility (Expt.  Xo.  48).  When  heated  in  close  vessels,  it  leaves  lead 
suboxide ;  but  when  heated  with  access  of  air,  the  yellow  oxide. 

c.  Lead  oxide,  produced  by  igniting  the  carbonate  or  oxalate, 
is  a  lemon-yellow  powder,  inclining  sometimes  to  a  reddish-yellow, 
or  to  a  pale  yellow.  When  this  yellow  lead  oxide  is  heated,  it 
assumes  a  brownish-red  color,  without  the  slightest  variation  of 
weight.  It  fuses  at  an  intense  red  heat.  Ignition  with  charcoal 
reduces  it.  When  exposed  to  a  white  heat,  it  rises  in  vapor.  Placed 
upon  moist  red  litmus  paper,  it  changes  the  color  to  blue.  When 
exposed  to  the  air,  it  slowly  absorbs  carbonic  acid.  Mixed  with 
ammonium  chloride  and  ignited,  it  is  converted  into  lead  chloride. 
Lead  oxide  in  a  state  of  fusion  readily  dissolves  silicic  acid  and  the 
earthy  bases  with  which  the  latter  may  be  combined. 

COMPOSITION. 

Pb 207  92-83 

O.  .'  16  7-17 


223  l«>n.  00 

d.  Lead  sulphate  is  a  heavy  white  powder.  It  dissolves,  at 
the  common  temperature,  in  22800  parts  of  pure  water  (Expt.  Xo. 
49*) ;  it  is  less  soluble  in  water  containing  sulphuric  acid  (1  part 
requiring  36500  parts — Expt.  Xo.  50) ;  it  is  far  more  readily  solu- 
ble in  water  containing  ammonium  salts ;  from  this  solution  it  may 
be  precipitated  again  by  adding  sulphuric  acid  in  excess  (Expt.  Xo. 
51).  It  is  almost  entirely  insoluble  in  common  alcohol.  Of  the 
ammonium  salts,  the  nitrate,  acetate,  and  tartrate  are  more  espe- 
cially suited  to  serve  as  solvents  for  lead  sulphate  :  the  two  latter 
salts  are  made  strongly  alkaline  by  addition  of  ammonia,  previous 
to  use  (WACKENRODER).  Lead  sulphate  dissolves  in  concentrated 
hydrochloric  acid,  upon  heating.  In  nitric  acid  it  dissolves  the 
more  readily,  the  more  concentrated  and  hotter  the  acid ;  water 
fails  to  precipitate  it  from  its  solution  in  nitric  acid ;  but  the  addi- 
tion of  a  copious  amount  of  dilute  sulphuric  acid  causes  its  precipi- 

*  According  to  G.  F.  RODWELL  1  part  dissolves  in  31696  parts  water  at  15° 
(Chem.  News,  1866,  50). 


172  FORMS.  [§  83. 

tation  from  this  solution.  The  more  nitric  acid  the  solution  con- 
tains, the  more  sulphuric  acid  is  required.  It  dissolves  sparingly 
in  concentrated  sulphuric  acid,  and  the  dissolved  portion  precipi- 
tates again  upon  diluting  with  water  (more  completely  upon  addi- 
tion of  alcohol).  A  moderately  concentrated  solution  of  sodium 
thiosulphate  dissolves  lead  sulphate  completely  even  if  cold,  more 
readily  if  warmed.  On  boiling,  the  solution  becomes  black,  from 
separation  of  a  small  quantity  of  lead  sulphide  (J.  LOWE*).  The 
solutions  of  alkali  carbonates  and  alkali  hydrogen  carbonates  con- 
vert lead  sulphate,  even  at  the  common  temperature,  completely 
into  lead  carbonate.  The  solutions  of  the  normal  alkali  carbonates, 
but  not  those  of  the  alkali  hydrogen  carbonates,  dissolve  some  lead 
oxide  in  this  process  (H.  RosEf).  Lead  sulphate  dissolves  readily 
in  hot  solutions  of  potassa  or  soda.  It  is  unalterable  in  the  air,  and 
at  a  gentle  red  heat ;  when  exposed  to  a  full  red  heat,  it  fuses  with- 
out decomposition  (Expt.  No.  52),  provided  always  reducing  gases 
be  completely  excluded — for,  if  this  is  not  the  case,  the  weight  will 
continually  diminish,  owing  to  reduction  to  sulphide  (EKDMANN^:). 
At  a  white  heat  the  whole  of  the  sulphuric  acid  gradually  escapes 
(BoussiNGAuivr  §).  When  it  is  ignited  with  charcoal,  lead  sulphide 
is  formed  at  first ;  if  the  heat  be  raised,  this  sulphide  reacts  on 
undecomposed  sulphate,  metallic  lead  and  sulphur  dioxide  being 
produced.  Fusion  with  potassium  cyanide  reduces  the  whole  of 
the  lead  to  the  metallic  state.  Lead  sulphate  mixed  with  sulphur 
and  exposed  to  intense  ignition  in  a  current  of  hydrogen  yields 
the  sulphide,  but  loss  can  scarcely  be  avoided  (compare  f). 

COMPOSITION. 

PbO     .     .     .     .     223  73.60 

SO..  80  26-40 


303  100-00 


e.  Lead  chloride  obtained  by  precipitation  is  a  white  crystalline 
powder.  It  separates  in  needles  from  a  hot  solution  containing  a 
certain  quantity  of  hydrochloric  acid;  occasionally  it  presents 
wedge-shaped  crystals,  or  when  separated  from  a  strong  hydro- 
chloric solution,  hexagonal  tables.  At  1Y°'7  water  dissolves  '946 


*  Journ.  f .  prakt.  Chem,  74,  348.  f  Pogg.  Annal.  95,  426. 

\  Journ.  f.  prakt.  Chem.  62,  381.  §  Zeitschr.  f.  anal.  Chem.  7,  244. 


§  83.]  BASES    OF   GROUP   V. 

per  cent.;  a  fluid  containing  15  per  cent,  of  hydrochloric  acid  of 
1-162  sp.  gr.  dissolves  -090 ;  a  fluid  containing  20  per  cent,  acid 
dissolves  '111  per  cent.;  a  fluid  containing  80  per  cent,  acid  dis- 
solves 1-498  per  cent.  Pure  hydrochloric  acid  of  the  above  strength 
dissolves  2'900  per  cent.  (J.  CARTER  BELL*).  Lead  chloride  is 
less  soluble  in  water  containing  nitric  acid  than  in  water  (1  part 
requires  1636  parts,  BISCHOF).  It  is  extremely  sparingly  soluble 
in  alcohol  of  TO  to  80  per  cent,,  and  altogether  insoluble  in  absolute 
alcohol.  It  is  unalterable  in  the  air.-  It  fuses  at  a  temperature 
below  red  heat,  without  loss  of  weight.  "When  exposed  to  a  higher 
temperature,  with  access  of  air,  it  volatilizes  slowly,  being  partially 
decomposed :  chlorine  gas  escapes,  and  a  mixture  of  lead  oxide  and 
chloride  remains. 

COMPOSITION. 

Pb 207-00  74-48 

01, 70-92  25-52 


277-92  100-00 

f.  Lead  sulphide,  prepared  in  the  wet  way,  is  a  black  precipi- 
tate, insoluble  in  water,  dilute  acids,  alkalies,  and  alkali  sulphides. 
In  precipitating  it  from  a  solution  containing  free  hydrochloric 
acid,  it  is  necessary  to  dilute  plentifully,  otherwise  the  precipitation 
will  be  incomplete.  Eveii  if  a  fluid  only  contain  2*5  per  cent.  HC1, 
the  whole  of  the  lead  will  not  be  precipitated  (M.  MARTIN  f).  It 
is  unalterable  in  the  air;  it  cannot  be  dried  at  100°  without 
-decomposition.  According  to  H.  ROSE  it  increases  perceptibly  in 
weight  by  oxidation  ;  in  the  case  of  long-protracted  drying  even 
becoming  a  few  per-cents  heavier. £  I  have  confirmed  his  state- 
ment (see  Expt.  X«>.  :>3 1.  If  lead  sulphide  mixed  with  sulphur  is 
heated  gently  in  a  current  of  hydrogen,  so  that  the  lower  quarter 
of  the  crucible  is  red  hot,  lead  sulphide  is  left  without  loss  of 
weight.  By  continuing  a  gentle  heat  the  weight  gradually  dimin- 
ishes; by  strong  ignition  the  loss  is  rapid.  This  loss  is  partly 
owing  to  volatilization  of  lead  sulphide,  but  mainly  to  escape  of 
sulphur  in  the  form  of  hydrogen  sulphide  and  formation  of  Pb2S, 
or  even  of  lead  (A.  SOUOHAY§).  It  dissolves  in  concentrated  hot 

*  Jour.  Chem.  Soc.  (2)  6,  355.  t  Journ.  f.  prakt.  Chem.  67,  374. 

\  Pogg.  Annal.  91,  110;  and  110,  134.        §  Zeitschr.  f.  anal.  Chem.  4,  63. 


174  FORMS.  [§  84. 

hydrochloric  acid,  with  evolution  of  hydrogen  sulphide.  In  mod- 
erately strong  nitric  acid  lead  sulphide  dissolves,  upon  the  applica- 
tion of  heat,  with  separation  of  sulphur ; — if  the  acid  is  rather  con- 
centrated, a  small  portion  of  lead  sulphate  is  also  formed.  Fuming 
nitric  acid  acts  energetically  upon  lead  sulphide,  and  converts  it 
into  sulphate  without  separation  of  sulphur. 

COMPOSITION. 

Pb     ........     207  86-61 

S  .  32  13-39 


239  100-00 

g.  For  the  composition  and  properties  of  lead  chromate,  see 
Chromic  acid,  §  93. 

§84. 

3.  MERCURY   IN   MERCUROUS   COMPOUNDS  ;    and  4.   MERCURY   IN 
MERCURIC   COMPOUNDS. 

Mercury  is  weighed  either  in  the  METALLIC  STATE,  as  MERCUROUS 
CHLORIDE,  or  as  SULPHIDE,  or  occasionally  as  MERCURIC  OXIDE. 

a.  Metallic  mercury  is  liquid  at  the  common  temperature ;  it 
has  a  tin-white  color.  When  pure,  it  presents  a  perfectly  bright 
surface.  It  is  quite  unalterable  in  the  air  at  the  common  tempera- 
ture. It  boils  at  360°.  It  evaporates,  but  very  slowly,  at  the 
ordinary  temperature  of  summer.  Upon  ]ong-continued  boiling 
with  water,  a  small  portion  of  mercury  volatilizes,  and  traces  escape 
along  with  the  aqueous  vapor,  whilst  a  very  minute  proportion 
remains  suspended  (not  dissolved)  in  the  water  (comp.  Expt.  'No. 
54).  This  suspended  portion  of  mercury  subsides  completely  after 
long  standing.  When  mercury  is  precipitated  from  a  fluid,  in  a 
very  minutely  divided  state,  the  small  globules  will  readily  unite 
to  a  large  one  if  the  mercury  be  perfectly  pure ;  but  even  the 
slightest  trace  of  extraneous  matter,  such  as  fat,  etc.,  adhering  to 
the  mercury  will  prevent  the  union  of  the  globules.  Mercury 
does  not  dissolve  in  hydrochloric  acid,  even  in  concentrated ;  it  is 
barely  soluble  in  dilute  cold  sulphuric  acid,  but  dissolves  readily  in 
nitric  acid. 

h.  Mercurous  chloride,  prepared  in  the  wet  way,  is  a  heavy 


§  84.]  BASES    OF    GROUP   V.  175 

white  powder.  It  is  almost  absolutely  insoluble  in  cold  water ;  in 
boiling  water  it  is  gradually  decomposed,  the  water  taking  up 
chlorine  and  mercury ;  upon  continued  boiling,  the  residue  acquires 
a  gray  color.  Highly  dilute  hydrochloric  acid  fails  to  dissolve  it 
at  the  common  temperature,  but  dissolves  it  slowly  at  a  higher 
temperature ;  upon  ebullition,  with  access  of  air,  the  whole  of  the 
mercurous  chloride  is  gradually  dissolved ;  the  solution  contains  mer- 
curic chloride  (Hg2Cl2  +  2HC1  +  O-=2HgCla  +  H2O).  When  acted 
upon  by  boiling  concentrated  hydrochloric  acid,  it  is  rather  speedily 
decomposed  into  mercury,  which  remains  undissolved,  and  mer- 
curic chloride,  which  dissolves.  Boiling  nitric  acid  dissolves  it  to 
mercuric  chloride  and  nitrate.  Chlorine  water  and  nitrohydrochlo- 
ric  acid  dissolve  it  to  mercuric  chloride,  even  in  the  cold.  Solutions 
of  ammonium  chloride,  sodium  chloride,  and  potassium  chloride, 
decompose  it  into  metallic  mercury  and  mercuric  chloride,  which 
latter  dissolves  ;  in  the  cold,  this  decomposition  is  but  slight ;  heat 
promotes  the  action.  It  is  soluble  in  hot  solution  of  mercurous 
nitrate,  and  still  more  in  that  of  mercuric  nitrate ;  on  cooling  it 
crystallizes  out  almost  completely  (DEBRAY*).  It  does  not  affect 
vegetable  colors ;  it  is  unalterable  in  the  air,  and  may  be  dried  at 
100°,  without  loss  of  weight ;  when  exposed  to  a  higher  degree  of 
heat,  though  still  below  redness,  it  volatilizes  completely,  without 
previous  fusion. 

COMPOSITION. 

Hg2 400-00  84-94 

Cl, 70-92  15-06 


470-92  100-00 

c.  Mercuric  sulphide,  prepared  in  the  wet  way,  is  a  black  pow- 
der, insoluble  in  water.  Dilute  hydrochloric  acid  and  dilute  nitric 
acid  fail  to  dissolve  it,  hot  concentrated  nitric  acid  scarcely  attacks 
it,  boiling  hydrochloric  acid  has  no  action  on  it.  By  prolonged 
heating  with  red  fuming  nitric  acid  it  is  finally  converted  into  a 
white  compound,  2HgS  +  Hg(NO3)2,  which  is  insoluble,  or  barely 
soluble,  in  nitric  acid.  It  dissolves  readily  in  nitrohydrochloric 
acid.  From  a  solution  of  mercuric  chloride  containing  much  free 
hydrochloric  acid,  the  whole  of  the  metal  cannot  be  precipitated  as 

*  Compt.  Rend.  70,  995. 


176  FORMS.  [§  84. 

sulphide  by  means  of  hydrogen  sulphide,  until  the  solution  is  prop- 
erly diluted.  Should  such  a  solution  be  very  concentrated,  mer- 
curous  chloride  and  sulphur  are  precipitated  (M.  MARTIN*).  Solu- 
tion of  potassa,  even  boiling,  fails  to  dissolve  it.  It  dissolves  in 
potassium  sulphide,  but  readily  only  in  presence  of  free  alkali.  It 
is  insoluble  in  potassium  hydrosulphide  and  in  the  corresponding 
-sodium  compound,  and  is  therefore  precipitated  from  its  solution 
in  potassium  or  sodium  sulphide  by  hydrogen  sulphide  or  by 
ammonium  hydrosulphide  (C.  BARFOEDf).  Small  but  distinctly 
perceptible  traces  dissolve  on  cold  digestion  with  yellowish  or  yel-~ 
low  ammonium  sulphide,  but  after  hot  digestion-  it  is  scarcely  possi- 
ble to  detect  any  traces  in  solution.;}:  Potassium  cyanide  and  sodium 
sulphite  do  not  dissolve  it.  On  account  of  the  solubility  of  mer- 
curic sulphide  in  potassium  sulphide,  it  is  impossible  to  precipitate 
mercury  by  means  of  ammonium  sulphide  completely  from  solutions 
containing  potassium  or  sodium  hydroxides  or  carbonates.  Such 
solutions  may  occur,  for  instance,  when  a  solution  of  mercuric 
chloride  contains  much  potassium  chloride,  or  sodium  chloride,  for, 
in  this  case,  no  mercuric  oxide  would  be  precipitated  on  the  addi- 
tion of  potassa  or  soda  (H.  ROSE§).  In  the  air  it  is  unalterable, 
even  in  the  moist  state,  and  at  100°.  When  exposed  -to  a  higher 
temperature,  it  sublimes  completely  and  unaltered. 

COMPOSITION. 

Hg 200  86-21 

S  32  13-79 


232  100-00 

d.  Mercuric  oxide,  prepared  in  the  dry  way,  is  a  crystalline 
brick-colored  powder,  which,  when  exposed  to  the  action  of  heat, 
changes  to  the  color  of  cinnabar,  and  subsequently  to  a  violet-black 
tint.  It  bears  a  tolerably  strong  heat  without  decomposition  ;  but 
when  heated  to  incipient  redness,  it  is  decomposed  into  mercury 
and  oxygen  ;  perfectly  pure  mercuric  oxide  leaves  no  residue  upon 
ignition.  Its  escaping  fumes  also  should  not  redden  litmus-paper. 
Water  takes  up  a  trace  of  mercuric  oxide,  acquiring  thereby  a  very 
weak  alkaline  reaction.  Hydrochloric  or  nitric  acid  dissolves  it 
readily. 

*  Journ.  f.  prakt.  Chem.  67,  376-  f  Zeitschr.  f.  anal.  Chem.  4,  436. 

\  Ib.  3,  140.  §  Pogg.  Annal.  110,  141. 


§  85.]  BASES    OF    GROUP    V.  177 


COMPOSITION. 


Hg 200  92-59 

O  16  7-41 


216  100-00 

'§  85. 
5.  COPPER. 

Copper  is  usually  weighed  in  the  METALLIC  STATE,  or  in  the 
form  of  CUPRIC  OXIDE,  or  of  CUPROUS  SULPHIDE.  Besides  these 
forms,  we  have  to  examine  CUPRIC  SULPHIDE,  CUPROUS  OXIDE,  and 

CUPROUS    SULPHOCYANATE. 

a.  Copper,  in  the  pure  state,  is  a  metal  of   a   peculiar  well- 
known  color.     It  fuses  only  at  a  white  heat.     Exposure  to  dry  air, 
or  to  moist  air,  free  from  carbon  dioxide,  leaves  the  fused  metal 
unaltered;    but   upon   exposure   to   moist  air   impregnated   with 
carbon  dioxide,  it  becomes  gradually  tarnished  and  coated  with  a 
film,  first  of  a  blackish-gray,  finally  of  a  bluish-green  color.     Pre- 
cipitated finely   divided  copper,   in   contact  with  water  and  air, 
oxidizes  far  more  quickly,  especially  at  an  elevated  temperature. 
On  igniting  copper  in  the  air,  it  oxidizes  superficially  to  a  varying 
mixture  of  cuprous  and  cupric  oxide.     In  hydrochloric  acid,-  in  the 
cold,  it  does  not  dissolve  if  air  be  excluded  ;  in  the  heat  it  dissolves 
but  slightly  if  the  metal  is  in  a  compact  state.     Finely  divided 
copper  on  the  contrary  dissolves  slowly  when  heated  with  strong 
hydrochloric  acid,  hydrogen  being  evolved  and  cuprous  chloride 
being  formed  (WELTZIEN*).     Copper  dissolves   readily  in   nitric 
acid.     In  ammonia  it  dissolves  slowly  if  free  access  is  given  to  the 
air ;  but  it  remains   insoluble   if   the   air   is   excluded.     Metallic 
copper  brought   into  contact  in  a  closed  vessel  with  solution  of 
cupric  chloride  in  hydrochloric  acid,  reduces  the  cupric  to  cuprous 
chloride,  an  atom  of  metal  being  dissolved  for  every  molecule  of 
chloride. 

b.  Cupric  oxide. — If  a  dilute,  cold,  aqueous  solution  of  a  cupric 
salt  is  mixed  with  solution  of  potassa  or  soda  in  excess,  a  light  blue 
precipitate  of  cupric  hydroxide,  Cu(OH),,  is  formed,  which  it  is 
found  difficult  to  wash.     If  the  precipitate  be  left  in  the  fluid 

*Ann.  d.  Cbem.  u.  Pharm.  136,  109. 


178  FORMS.  [§  85. 

from  which  it  has  been  precipitated,  it  will,  even  at  a  summer 
heat,  gradually  change  to  brownish-black,  passing,  with  separation 
of  water,  into  6CuO  -f-  H2O  (SOUCHAY).  This  transformation  is 
immediate  upon  heating  the  fluid  nearly  to  boiling.  The  fluid 
filtered  off  from  the  black  precipitate  is  free  from  copper.  It 
follows  from  this  that  the  black  precipitate  is  insoluble  in  dilute 
potassa.  Concentrated  potassa  or  soda  on  the  contrary  dissolves  the 
hydroxide,  and  on  long  warming  even  the  black  oxide  (O.  Low*). 
The  resulting  blue  solutions  remain  clear  on  boiling,  even  if  mixed 
with  some  water ;  but  if  boiled  after  being  much  diluted  the  whole 
of  the  copper  will  separate  as  black  oxide.  If  a  solution  of  a 
cupric  salt  contains  non-volatile  organic  substances,  the  addition  of 
alkali  in  excess  will,  even  upon  boiling,  fail  to  precipitate  the 
whole  of  the  copper.  The  hydrated  cupric  oxide,  6CuO  -f-  H2O, 
precipitated  with  potassa  or  soda  from  hot  dilute  solutions  obsti- 
nately retains  a  portion  of  the  precipitant ;  it  may,  however,  be 
completely  freed  from  this  by  washing  with  boiling  water.  The 
precipitated  oxide  after  ignition,  or  the  oxide  prepared  by  decom- 
posing cupric  carbonate  or  nitrate  by  heat,  is  a  brownish-black,  or 
black  powder,  the  weight  of  which  remains  unaltered  even  upon 
strong  ignition  over  the  gas-  or  spirit-lamp,  provided  all  reducing 
gases  be  excluded  (Expt.  No.  56).  If  cupric  oxide  is  exposed  to  a 
heat  approaching  the  fusing  point  of  metallic  copper,  it  fuses, 
yields  oxygen,  and  becomes  Cu5O3  (FAVRE  and  MAUMENE).  It  is 
very  readily  reduced  by  ignition  with  charcoal,  or  under  the  in- 
fluence of  reducing  gases ;  heated  in  the  air  for  a  long  time,  the 
reduced  metallic  copper  re-oxidizes.  Mixed  with  sulphur  and 
ignited  in  a  current  of  hydrogen,  towards  the  end  strongly,  cupric 
oxide  passes  into  cuprous  sulphide  (Cu2S — H.  ROSE).  Cupric  oxide, 
in  contact  with  the  atmosphere,  absorbs  water ;  less  rapidly  after 
being  strongly  ignited  (Expt.  No.  57).  It  is  nearly  insoluble  in 
water;  but  it  dissolves  readily  in  hydrochloric  acid,  nitric  acid, 
&c.;  less  readily  in  ammonia,  It  does  not  affect  vegetable  colors. 

COMPOSITION. 

Cu 63-40  79-85 

O  16-00  20-15 


79-40  100-00 


*  Zeitschr.  f.  anal.  Chem.  9,  463, 


§  85.J  BASES    OF    GROUP    V.  179 

c.  Cupric  sulphide,  prepared  in  the  wet  way,  is  a  brownish- 
Muck,  or  black  precipitate,  almost  absolutely  insoluble  in  water.* 
When  exposed  to  the  air  in  a  moist  state,  it  acquires  a  greenish 
tint  and  the  property  of  reddening  litmus  paper,  cupric  sulphate 
being  formed.     Hence  the  sulphide  must  be  washed  with  water 
containing   hydrogen   sulphide.      It   dissolves   readily   in   boiling 
nitric  acid,  with  separation   of  sulphur.     Hydrochloric  acid  dis- 
solves it  with  difficulty.    This  is  the  reason  why  hydrogen  sulphide 
precipitates  copper  entirely  from  solutions  which  contain  even  a 
very  large  amount  of  free  hydrochloric  acid  (GnuNDMANNf).    Only 
when  we  dissolve  a  copper  salt  directly  in  pure  hydrochloric  acid 
of  1*1  sp.  gr.  does  any  copper  remain  unprecipitated  (M.  MARTINA). 
It  does  not   dissolve   in   solutions   of   potassa   and   of  potassium 
sulphide,  particularly  if   these   solutions  be  boiling;  it  dissolves 
perceptibly   in  colorless,  and  much  more   readily  in   hot  yellow 
ammonium  sulphide.    Potassium  cyanide  dissolves  the  freshly  pre- 
cipitated sulphide  readily  and  completely.     Upon  intense  ignition 
in  a  current  of  hydrogen  it  is  converted  into  pure  Cu,S. 

d.  If  the  blue  solution  which  is  obtained  upon  adding  to  solu- 
tion of  copper  tartaric  acid  and  then  soda  in  excess,  is  mixed  with 
solution  of  grape  sugar  or  sugar  of  milk,  and  heat  applied,  an 
orange-yellow  precipitate  of  cuprous  hydroxide  is  formed,  which 
contains  the  whole  of  the  copper  originally  present  in  the  solu- 
tion, and  after  a  short  time,  more  particularly  upon  the  applica- 
tion of  a  stronger  heat,  turns  red,  owing  to  the  conversion  of  the 
hydroxide  into  anhydrous  cuprous  oxide  (Cu2O).     The  precipitate, 
which  is  insoluble  in  water,  retains  a  portion  of  alkali  with  con- 
siderable tenacity.     When  treated  with  dilute  sulphuric  acid,  it 
gives  cupric  sulphate  which   dissolves,  and  metallic  copper  which 
separates. 

e.  Cuprous  sulphocyanate,  Cu2(CNS)a,  which  is  always  formed 
when  potassium  sulphocyanate  is  added  to  a  solution  of  copper,  mixed 
with  sulphurous  or  hypophosphorous  acid,  is  a  white  precipitate  in- 
soluble in  water,  as  well  as  in  dilute  hydrochloric  or  sulphuric 
acid.    Dried  at  115°,  the  salt  retains  from  1  to  3  per  cent,  of  water, 
which  is  driven  off  only  by  heating  to  incipient  decomposition ; 
it   is,  therefore,  not  well   adapted   for   direct   weighing.     When 

*  In  some  experiments  that  I  made  when  examining  the  Weilbach  water,  I 
found  that  about  950000  parts  of  water  are  required  to  dissolve  1  part  of  CuS. 
f  Journ.  f.  prakt.  Chem.  73,  241.  \  Ib.  67,  375, 


180  FORMS.  [§  86. 

ignited- with  sulphur,  with  exclusion  of  air,  it  changes  to  Cu2S 
(RivoT*).  When  heated,  with  hydrochloric  acid  and  potassium 
chlorate,  or  with  sulphuric  acid  and  nitric  acid,  it  is  dissolved 
and  suffers  decomposition.  Solutions  of  potassa  and  soda  separate 
hydrated  cuprous  oxide,  with  formation  of  sulphocyanate  of  the 
alkali  metal. 

f.  Cuprous  sulphide,  produced  by  heating  CuS  in  a  current  of 
hydrogen  or  Cu,(GN"S)a  with  sulphur,  is  a  grayish-black  crystalline 
mass,  which  may  be  ignited  and  fused  without  decomposition  if 
the  air  is  excluded. 

COMPOSITION. 

Cu,    ....     126-80  79-85 

S  .  32-00  20-15 


158-80  100-00 

§  86. 
6.  BISMUTH. 

Bismuth  is  weighed  as  OXIDE,  as  METAL,  or  as  CHKOMATE 
(BiaO,2CrO4).  Besides  these  compounds,  we  have  to  study  here 

the  BASIC    CARBONATE,  the    BASIC    NITRATE,  the    BASIC    CHLORIDE,  and 

the  SULPHIDE. 

a.  Bismuth  trioxide,  prepared  by  igniting  the  carbonate  or 
nitrate,  is  a  pale  lemon-yellow  powder  which,  under  the  influence 
of  heat,  assumes  transiently  a  dark  yellow  or  reddish-brown  color. 
When  heated  to  intense  redness,  it  fuses,  without  alteration  of 
weight.  Ignition  with  charcoal,  or  in  a  current  of  carbon  mon- 
oxide, reduces  it  to  the  metallic  state.  Fusion  with  potassium 
cyanide  also  effects  its  complete  reduction  (II.  RosEf).  It  is  in- 
soluble in  water,  and  does  not  affect  vegetable  colors.  It  dissolves 
readily  in  those  acids  which  form  soluble  salts  with  it.  When 
ignited  with  ammonium  chloride  it  gives  metallic  bismuth,  the 
reduction  being  attended  with  deflagration. 

COMPOSITION. 

Bia    .     .     .     .     .     416  89-655 

O3 48  10-345 


464  100-000 


*Ib.  62,  252.  f  Journ.  f.  prakt.  Ohem.  61,  188. 


§  86.]  EASES    OF   GROUP   V.  181 

b.  Metallic  bismuth  is  white,  with  a  reddish  tinge,  moderately 
hard,  brittle,  with  a  tendency  to  crystallize.     It  fuses  at  264°,  and 
at  a  low  white  heat  volatilizes.     It  does  not  oxidize  in  the  air  at 
the  ordinary  temperature,  but  with  the  co-operation  of  water  it 
oxidizes  slowly,  more  speedily  on  fusion.     It  dissolves  in  dilute 
nitric  acid. 

c.  Bismuth  carbonate. — Upon  adding  ammonium  carbonate  in 
excess  to  a  solution  of  bismuth,  free  from  hydrochloric  acid,  a 
white  precipitate  of  basic  bismuth  carbonate  (Bi3OzCO3)  is  imme- 
diately formed ;  part  of  this  precipitate,  however,  redissolves  in 
the  excess  of  the  precipitant.     But  if  the  fluid  with  the  precipitate 
be  heated  before  filtration,  the  filtrate  will  be  free  from  bismuth. 
(Potassium  carbonate   likewise   precipitates   solutions  of  bismuth 
completely ;  but  the  precipitate  in  this  case  invariably  contains 
traces  of  potassium,  which  it  is  very  difficult  to  remove  by  wash- 
ing.    Sodium    carbonate    precipitates   solutions   of   bismuth   less 
completely.)     The  precipitate  is  easily  Avashed;   it  is  practically 
insoluble   in   water,  but   dissolves  readily,  with  effervescence,  in 
hydrochloric  and  nitric  acids.     Upon  ignition  it  leaves  the  oxide. 

d.  The  basic  bismuth  nitrate,   which  is  obtained   by  mixing 
with  water  a  solution  of  the  nitrate  containing  little  or  no  free 
acid,  presents  a  white,  crystalline  powder.     It  cannot  be  washed 
with  pure  cold  water  without  suffering  a  decided  alteration.     It 
becomes  more  basic,  while  the  washings  show  an  acid  reaction,  and 
contain  bismuth.     If  the  basic  salt,  however,  be  washed  with  cold 
water  containing  -^-^  of   ammonium  nitrate,  no   bismuth  passes 
through  the  filter.     The  solution  of  ammonium  nitrate  must  not 
be  warm.     These  remarks  only  apply  in  the  absence  of  free  nitric 
acid  (J.  LOWE*).     On  ignition  the  basic  nitrate  passes  into  the 
oxide. 

e.  Basic  bi.$m  >>th-  Morifo,  formed  by  adding  much  water  to 
solution   of    bismuth   containing    hydrochloric    acid    or    sodium 
chloride,  is  a  brilliant  white  powder  (BiOCl  after  drying  at  100°). 
It  is  insoluble  in  water,  but  dissolves  in  concentrated  hydrochloric 
or  nitric  acid.     Fused  with  potassium  cyanide  it   gives  metallic 
bismuth. 

f.  Bismuth   chromate  (Bi2O3,2CrO3),  which   is  produced    by 
adding  potassium  dichromate,  slightly  in  excess,  to  a  solution  of 

*  Ib.  74.  341. 


182  FOBMS.  [§  87. 

bismuth  nitrate  as  neutral  as  possible,  is  an  orange-yellow,  dense, 
readily-subsiding  precipitate,  insoluble  in  water,  even  in  presence 
of  some  free  chromic  acid,  but  soluble  in  hydrochloric  acid  and 
nitric  acid.  It  may  be  dried  at  100°-112°  without  decomposition 

(LOWE*). 

COMPOSITION. 

» o 


o    /  Q>v"v,,       Bi^  464-00         69-78 


^  O  x 

664-96       100-00 

g.  Bismuth  trisulphide,  prepared  in  the  wet  way,  is  a  brownish 
black,  or  black  precipitate,  insoluble  in  water,  dilute  acids,  alkalies, 
alkali  sulphides,  sodium  sulphite,  and  potassium  cyanide.  In 
moderately  concentrated  nitric  acid  it  dissolves,  especially  on 
warming,  to  nitrate,  with  separation  of  sulphur.  Hence  in  pre- 
cipitating bismuth  from  a  nitric  acid  solution,  care  should  be 
taken  to  dilute  sufficiently.  Hydrochloric  acid  impedes  the  pre- 
cipitation by  hydrogen  sulphide  only  when  a  very  large  excess  is 
present,  and  the  fluid  is  quite  concentrated.  The  sulphide  does 
not  change  in  the  air.  Dried  at  100°,  it  continually  takes  up 
oxygen  and  increases  slightly  in  weight ;  if  the  drying  is  protracted 
this  increase  may  be  considerable  (Expt.  No.  58).  Fused  with 
potassium  cyanide,  it  is  completely  reduced  (H.  ROSE).  Reduction 
takes  place  more  slowly  by  ignition  in  a  current  of  hydrogen. 

COMPOSITION. 

Bi, 416  81-25 

S$ 96  18-75 


512  100-00 

§  87. 
7.  CADMIUM. 

Cadmium  is  weighed  either  as  OXIDE  or  as  SULPHIDE.  Besides 
these  substances,  we  have  to  examine  CADMIUM  CARBON  AT  K. 

a.  Cadmium  oxide,  produced  by  igniting  the  carbonate  or 
nitrate,  is  a  yellowish-brown  or  reddish-brown  powder.  The  appli- 

*  Journ.  f.  prakt.  Chem.  67,  291. 


§87.]  BASES    OF    GROTP    V.  183 

cation  of  a  white  heat  fails  to  fuse,  volatilize,  or  decompose  it ;  it 
is  insoluble  in  water,  hut  dissolves  readily  in  acids ;  it  does  not 
alter  vegetable  colors.  Ignition  with  charcoal,  or  in  a  current  of 
hydrogen,  carbon  monoxide,  or  carburetted  hydrogen,  reduces  it 
readily,  the  metallic  cadmium  escaping  in  the  form  of  vapor. 

COMPOSITION. 

Cd     !     .     .     .     .       112  87-50 

O  16  12-50 


128  100-00 

l>.  Cadmium  carbonate  is  a  white  precipitate,  insoluble  in  water 
and  the  fixed  alkali  carbonates,  and  extremely  sparingly  soluble  in 
ammonium  carbonate.  It  loses  its  water  completely  upon  drying. 
Ignition  converts  it  into  oxide. 

c.  Cadmium  sulphide,  produced  in  the  wet  way,  is  a  lemon- 
yellow  to  orange-yellow  precipitate,  insoluble  in  water,  dilute  acids, 
alkalies,  alkali  sulphides,  sodium  sulphite,  and  potassium  cyanide 
(Expt.  No.  59).  It  dissolves  readily  in  concentrated  hydrochloric- 
acid,  with  evolution  of  hydrogen  sulphide.  In  precipitating,  there- 
fore, with  hydrogen  sulphide,  a  cadmium  solution  should  not 
contain  too  much  hydrochloric  acid,  and  should  be  sufficiently 
diluted.  The  sulphide  dissolves  readily  in  dilute  sulphuric  acid 
on  heating.  It  dissolves  in  moderately  concentrated  nitric  acid, 
with  separation  of  sulphur.  It  may  be  washed,  and  dried  at  100° 
or  105°,  without  decomposition.  Even  on  gentle  ignition  in  a 
current  of  hydrogen,  it  volatilizes  in  appreciable  amount  (H. 
ROSE*),  partially  unchanged,  partially  as  metallic  vapor. 

COMPOSITION. 

Cd 112  77-78 

S  ...       32  22-22 


100-00 


Pogg.  Annal.  110,  134 


184  FORMS.  [§§  88,  89. 

METALS   OF  THE   SIXTH   GROUP. 

§  88. 
1.  GOLD. 

Gold  is  always  weighed  in  the  metallic  state.  Besides  METALLIC 
GOLD,  we  have  to  consider  the  TKISULPHIDE  or  AURIC  SULPHIDE. 

a..  Metallic  gold,  obtained  by  precipitation,  presents  a  blackish- 
brown  powder,  destitute  of  metallic  lustre,  which  it  assumes,  how- 
ever, upon  pressure  or  friction  ;  when  coherent  in  a  compact  mass, 
it  exhibits  the  well-known  bright  yellow  color  peculiar  to  it.  It 
fuses  only  at  a  white  heat,  and  resists,  accordingly,  all  attempts  at 
fusion  over  a  spirit-lamp.  It  remains  wholly  unaltered  in  the  air 
and  at  a  red  heat,  and  is  not  in  the  slightest  degree  affected  by 
water,  nor  by  any  simple  acid.  Nitrohydrochloric  acid  dissolves 
it  to  trichloride.  Hot  concentrated  sulphuric  acid  containing  a 
little  nitric  acid  dissolves  gold,  especially  if  in  a  finely  divided 
condition,  to  a  yellow  fluid,  from  which  it  is  thrown  down  again 
by  water  (J.  SPILLED). 

1.  Auric  sulphide. — When  hydrogen  sulphide  is  transmitted 
through  a  cold  dilute  solution  of  auric  chloride,  the  whole  of  the 
gold  separates  as  auric  sulphide.  Au2S3,  in  form  of  a  brownish- 
black  precipitate.  If  this  precipitate  is  left  in  the  fluid,  it  is 
gradually  transformed  into  metallic  gold  and  free  sulphuric  acid. 
Upon  transmitting  hydrogen  sulphide  through  a  warm  solution 
of  auric  chloride,  aurous  sulphide  Au2S  precipitates,  with  formation 
of  sulphuric  and  hydrochloric  acids. 

Auric  sulphide  is  insoluble  in  water,  hydrochloric  acid,  and 
nitric  acid,  but  dissolves  in  nitrohydrochloric  acid.  Colorless  am- 
monium sulphide  fails  to  dissolve  it;  but  it  dissolves  almost 
entirely  in  yellow  ammonium  sulphide,  and  completely  upon 
addition  of  potassa.  It  dissolves  in  potassa,  with  separation  of 
gold.  Yellow  potassium  sulphide  dissolves  it  completely.  It  dis- 
solves in  potassium  cyanide.  Exposure  to  a  moderate  heat  reduces 
it  to  the  metallic  state. 

§  89. 

2.  PLATINUM. 
Platinum  is  invariably  weighed  in  the  METALLIC  STATE  ;  it  is 


f  Chern.  News,  14,  256. 


§90.]  METALS  OF  <;Korp  vi.  185 

generally   precipitated   as   AMMOXITM    PLATINIC    CHLORIDE,   or   as 

POTASSIUM  PLATINIC  CHLORIDE,  rarely  as  PLATINIC    SULPHIDE. 

a.  Metallic  platinum,  produced  by  igniting  ammonium  platinic 
chloride,  or  potassium  platinic  chloride,  presents  the  appearance  of 
a  gray,  lustreless,  porous  mass  (spongy  platinum).  The  fusion  of 
platinum  can  be  effected  only  at  the  very  highest  degrees  of  heat. 
It  remains  wholly  unaltered  in  the  air,  and  in  the  most  powerful 
furnaces.  It  is  not  attacked  by  water,  or  simple  acids,  and  scarcely 
by  aqueous  solutions  of  the  alkalies.  Nitrohydrochloric  acid  dis- 
solves it  to  platinic  chloride. 

J.  The  properties  of  potassium  platinic  chloride,  and  those  of 
ammonium  platinic  chloride,  have  been  given  already  in  §§  68 
and  TO  respectively. 

c.  Platinic  sulphide. — When  a  concentrated  solution  of  pla- 
tinic chloride  is  mixed  with  hydrogen  sulphide  water,  or  when 
hydrogen  sulphide  gas  is  transmitted  through  a  rather  dilute 
solution  of  the  chloride,  no  precipitate  forms  at  first ;  after  stand- 
ing some  time,  however,  the  solution  turns  brown,  and  finally  a 
precipitate  subsides.  But  if  the  mixture  of  solution  of  platinic 
chloride,  with  hydrogen  sulphide  in  excess,  is  gradually  heated 
(finally  to  ebullition),  the  whole  of  the  platinum  separates  as 
platinic  sulphide  (free  from  any  admixture  of  platinic  chloride). 
Platinic  sulphide  is  insoluble  in  water  and  in  simple  acids  ;  but  it 
dissolves  in  nitrohydrochloric  acid.  It  dissolves  partly  in  caustic 
alkalies,  with  separation  of  platinum,  and  completely  in  alkali 
sulphides,  especially  the  polysulphides  if  used  in  sufficient  excess. 
When  hydrogen  sulphide  is  transmitted  through  water  holding 
minutely  divided  .platinic  sulphide  in  suspension,  the  sulphide, 
absorbing  hydrogen  sulphide,  acquires  a  light  grayish-brown  color  ; 
the  hydrogen  sulphide  thus  absorbed,  separates  again  upon  exposure 
to  the  air.  When  moist  platinic  sulphide  is  exposed  to  the  air,  it 
is  gradually  decomposed,  being  converted  into  metallic  platinum 
and  sulphuric  acid.  Ignition  in  the  air  reduces  platinic  sulphide  to 
metallic  platinum. 

§  90. 
3.   ANTIMONY. 

Antimony  is  weighed  as  ANTIMONIOUS  SULPHIDE,  as  ANTIMONY 
TETROXIDE  (or  ANTIMONIOUS  ANTIMONATE),  or  more  rarely  in  the 
METALLIC  state. 


186  FORMS.  [§  90. 

a.  Upon  transmitting  hydrogen  sulphide  through  a  solution  of 
antimonious  chloride  mixed  with  tartaric  acid,  an  orange  precipi- 
tate of  amorphous  antimonious  sulphide  is  obtained,  mixed  at  first 
with  a  small  portion  of  basic  antimony  chloride.  However,  if  the 
fiuid  is  thoroughly  saturated  with  hydrogen  sulphide,  and  a  gentle 
heat  applied,  the  chloride  mixed  with  the  precipitate  is  decom- 
posed, and  pure  antimonious  sulphide  obtained.  Antimonious 
sulphide  is  insoluble  in  water  and  dilute  acids ;  it  dissolves  in  con- 
centrated hydrochloric  acid,  with  evolution  of  hydrogen  sulphide. 
In  precipitating  with  hydrogen  sulphide,  therefore,  antimony 
solutions  should  not  contain  too  much  free  hydrochloric  acid,  and 
should  be  sufficiently  diluted.  The  amorphous  antimonious  sul- 
phide dissolves  readily  in  dilute  potassa,  ammonium  sulphide,  and 
potassium  sulphide,  sparingly  in  ammonia,  very  slightly  in  ammo- 
nium carbonate,  and  not  at  all  in  hydrogen  potassium  sulphite. 
The  amorphous  sulphide,  dried  in  the  desiccator  at  the  ordinary 
temperature,  loses  very  little  weight  at  100°;  if  kept  for  some 
time  at  this  latter  temperature  its  weight  remains  constant.  But 
it  still  retains  a  little  water,  which  does  not  perfectly  escape  even 
at  190°,  but  at  200°  the  sulphide  becomes  anhydrous,  turning 
black  and  crystalline  (II.  KOBE*  and  Expt.  No.  60).  Ignited 
gently  in  a  stream  of  carbon  dioxide,  the  weight  of  this  anhydrous 
sulphide  remains  constant;  at  a  stronger  heat  a  small  amount 
volatilizes.  The  amorphous  sulphide,  if  long  exposed  to  the  action 
of  air,  in  presence  of  water,  slowly  takes  up  oxygen,  so  that  on 
treatment  with  tartaric  acid  it  yields  a  filtrate  containing  anti- 
mony. 

Antimonic  sulphide  is  insoluble  in  water,  also  in  water  con- 
taining hydrogen  sulphide.  It  dissolves  completely  in  ammonia, 
especially  on  warming;  traces  only  dissolve  in  ammonium  car- 
bonate. On  heating  dried  antimonic  sulphide  in  a  current  of 
carbon  dioxide  2  atoms  of  sulphur  escape,  black  crystalline  anti- 
monious sulphide  remaining. 

On  treating  antimonious  or  antimonic  sulphide  with  fuming 
nitric  acid  violent  oxidation  sets  in.  We  obtain  first  antimonic 
acid  and  pulverulent  sulphur  ;  on  evaporating  to  dryness  antimonic 
acid  and  sulphuric  acid  ;  and  lastly  on  igniting  antimony  tetroxide. 
The  same  antimony  tetroxide  is  obtained  by  igniting  the  sulphide 

*  Journ.  f.  prakt.  Chem.  59,  331. 


§  90.  J  METALS    OF   GROUP   VI.  187 


with  30  to  50  times  its  amount  of  mercuric  oxide 
[According  to  later  investigations  of  BuxsEN,t  the  temperature 
necessary  to  reduce  Sb2O.  to  Sb2O4  lies  so  near  that  which  reduces 
SbaO4  to  Sb3O3  that  it  is  not  easy  to  bring  antimony  into  SbaO4  for 
weighing.  It  is  possible  only  by  using  a  large  covered  platinum  or 
rather  large  open  porcelain  crucible  (by  suitable  choice  of  size  of 
crucible  and  intensity  of  flame)  and  heating  with  a  gas  blast  lamp 
so  that  the  bottom  only  of  the  crucible  reaches  a  strong  red  heat, 
to  drive  off  exactly  one  atom  of  oxygen  from  Sb3O6.]  Ignition  in 
a  current  of  hydrogen  converts  the  sulphides  of  antimony  into  the 
metallic  state. 

COMPOSITION. 

Sb,     .     .     .     .     244-00  71-77 

S8       ....       96-00  28-23 


340-00  100-00 

b.  Antimony  tetroxide  is  a  white  powder,  which,  when  heated, 
acquires  transiently  a  yellow  tint ;  it  is  infusible ;  it  loses  weight 
when  ignited  intensely  in  a  small  platinum  crucible  with  a  gas 
blast  flame  (BuNSENf).  It  is  almost  insoluble  in  water,  and  dis- 
solves in  hydrochloric  acid  with  very  great  difficulty.  It  undergoes 
no  alteration  on  treatment  with  ammonium  sulphide.  It  manifests 
an  acid  reaction  when  placed  upon  moist  litmus-paper. 

COMPOSITION. 

Sba 244  79-22 

0 64  20-78 


308  100-00 

c.  Metallic  antimony*  produced  in  the  wet  way,  by  precipita- 
tion, presents  a  lustreless  black  powder.  It  may  be  dried  at  100° 
without  alteration.  It  fuses  at  a  moderate  red  heat.  Upon  ignition 
in  a  current  of  gas,  e.g.,  hydrogen,  it  volatilizes,  without  formation 
of  antimonetted  hydrogen.  Hydrochloric  acid  has  very  little 
action  on  it,  even  when  concentrated  and  boiling.  Nitric  acid 
converts  it  into  antimonious  oxide,  mixed  with  more  or  less 

*  Annal.  de  Chem.  u.  Pharm.  106,  3.     f  Zeitschr.  f .  anal.  Chem.  1879,  268. 


188  FORMS.  [g  91. 

antimony  tetroxide,  according  to  the  concentration  of  the  nitric 
acid. 

§91. 

4.  TIN  IN  STANNOUS  COMPOUNDS  ;   and  5.  TIN  IN  STANNIC 
COMPOUNDS. 

Tin  is  generally  weighed  in  the  form  of  STANNIC  OXIDE  ;  be- 
sides stannic  oxide,  we  have  to  examine  stanuous  sulphide  and 
stannic  sulphide. 

a.  Stannic  oxide. — If  a  solution  of  an  alkali,  sodium  sulphate 
or  ammonium  nitrate  is  added  to  a  solution  of  stannic  chloride, 
stannic  acid  (H2SnO3)  is  precipitated.  This  precipitate  is  soluble 
in  excess  of  soda,  and  does  not  separate  again  even  on  the  addition 
of  a  large  quantity  of  soda  (C.  F.  BAKFOED*).  It  is  also  readily 
soluble  in  hydrochloric  acid. 

By  the  action  of  nitric  acid  on  metallic  tin,  or  by  evaporating 
a  solution  of  tin  with  an  excess  of  nitric  acid,  a  white. residue  is 
obtained  which  is  metastannic  acid  (Sn6H10O16  ?).  This  residue  is 
insoluble  in  water,  but  very  slightly  soluble  in  nitric  acid,  or 
sulphuric  acid.  By  heating  with  hydrochloric  acid  it  does  not 
dissolve,  but  is  changed  to  metastannic  chloride,  which  is  soluble 
in  water  after  removal  of  the  excess  of  hydrochloric  acid.  Soda 
added  to  a  solution  of  metastannic  chloride  precipitates  sodium 
metastaiinate,  which  is  insoluble  in  excess  of  soda  and  in  weak 
alcohol.  Upon  intense  ignition,  both  stannic  and  metastannic  acids 
are  converted  into  stannic  oxide.  Mere  heating  to  redness  is  not 
sufficient  to  expel  all  the  water  (DuMAsf). 

Stannic  oxide  is  a  straw-colored  powder,  which  under  the 
influence  of  heat,  transiently  assumes  a  different  tint,  varying  from 
bright  yellow  to  brown.  It  is  insoluble  in  water  and  acids,  and 
does  not  alter  the  color  of  litmus-paper.  Mixed  with  ammonium 
chloride  in  excess,  and  ignited,  it  volatilizes  completely  as  stannic 
chloride.  If  stannic  oxide  is  fused  with  potassium  cyanide,  all  the 
tin  is  obtained  in  form  of  metallic  globules,  which  may  be  com- 
pletely, and  without  the  least  loss  of  metal,  freed  from  the  adhering 
slag,  by  extracting  with  dilute  alcohol,  and  rapidly  decanting  the 
fluid  from  the  tin  globules  (H.  ROSE;):). 

*  Zeitschr.  f.  anal.  Chem.  7,  260.     f  Annal.  d.  Chem.  u.  Pharm.  105,  104. 
\  Journ.  f.  prakt.  Chem.  61,  189. 


§  91.]  METALS    OF   GROUP   VI.  189 

COMPOSITION. 

Sn 118  78-67 

O, 32  21-33 

150  100-00 

b.  Hydrated  stannous  sulphide  forms   a   brown   precipitate, 
insoluble  in  water,  hydrogen  sulphide  water,  and  dilute  acids.     In 
precipitating  tin  from  stannous  solutions  by  means  of  hydrogen 
sulphide,  free  hydrochloric  acid  must  not  be  present  in  too  large 
amount,  and  the  solution  must  be  diluted  sufficiently.     Ammonia 
fails  to  dissolve  it ;  but  it  dissolves  pretty  readily  in  yellow  ammo- 
nium sulphide,   and  in  yellow  potassium  sulphide ;    it  dissolves 
readily  in  hot  concentrated  hydrochloric  acid.    Heated,  with  exclu- 
sion of  air,  it  loses  its  water, and  is  rendered  anhydrous;  when  ex- 
posed to  the  continued  action  of  a  gentle  heat,  with  free  access  of 
air,  it  is  converted  into  sulphur  dioxide,  which  escapes,  and  stannic 
oxide,  which  remains. 

c.  Hydrated  stannic  sulphide,  precipitated  by  acids  from  the 
solution  of  its  alkali  sulphur  salts,  is  a  light-yellow  precipitate.    In 
washing  with  pure  water,  it  is  inclined  to  yield  a  turbid  filtrate 
and  to  stop  up  the  pores  of  the  filter ;  this  annoyance  is  got  over 
by  washing  with  water  containing  sodium  chloride,   ammonium 
acetate,  or  the  like  (BuxsEx).     On  drying,  the  precipitate  assumes 
a  darker  tint.     It  is  insoluble  in  water ;  it  dissolves  with  difficulty 
in  ammonia,  but  readily  in  potassa,  alkali  sulphides,  and  hot  con- 
centrated hydrochloric  acid.    It  is  insoluble  in  hydrogen  potassium 
sulphite.     In  precipitating  tin  from,  stannic  solutions  by  hydrogen 
sulphide,  the  solution  should  not  contain  too  much  free  hydro- 
chloric acid,  and   should   be   sufficiently   diluted.    According   to 
C.   F.   BARFOED*  the   precipitates   thus   produced   are   not   pure 
hydrated  stannic  sulphide,  but  a  mixture  of  this  with  stannic  or 
metastannic  acid,  as  the  case   may  be.     The  precipitate  thrown 
down  from  ordinary  stannic  chloride  keeps  its  yellow  color  even 
after  long  standing  in  the  fluid,  and  dissolves  completely  in  excess 
of  soda ;  that  thrown  down  from  the  metastannic  chloride  is  first 
white  and  becomes  gradually  yellow,  it  turns  brown  on  standing 
in  the  fluid  and   dissolves  in  excess  of  soda,  leaving,  however,  a 
considerable  residue  of  sodium  metastannate.     When  heated,  with 

*  Zeitschr.  f.  anal.  Chem.  7,  261. 


190  FORMS.  [§  92. 

exclusion  of  air,  stannic  sulphide  loses  its  water  of  hydration,  and, 
at  the  same  time,  according  to  the  degree  of  heat,  one-half  or  one- 
fourth  of  its  sulphur,  becoming  converted  either  into  stannous 
sulphide  or  the  sesquisulphide  of  tin ;  when  heated  very  slowly, 
-with  free  access  of  air,  it  is  converted  into  stannic  oxide,  with  dis- 
engagement of  sulphur  dioxide. 

§92. 

6.  ARSENIC  OF  ARSENIOUS  COMPOUNDS  ;  and  7.  ARSENIC  OF 
ARSENIC  COMPOUNDS. 

ARSENIC  is  weighed  either  as  LEAD  ARSENATE,  as  ARSENIOUS 

SULPHIDE,  aS    AMMONIUM  MAGNESIUM  ARSENATE,  as  MAGNESIUM  PYRO- 

ARSENATE,  or  as  URANYL  PYROARSENATE ;  besides  these  forms,  we 
have  here  to  examine  also  ARSENIO-MOLYBDATE  OF  AMMONIUM. 

a.  Lead  arsenate,  in  the  pure  state,  is  a  white  powder,  which 
agglutinates  when  exposed  to  a  gentle  red  heat,  at  the  same  time 
transitorily  acquiring  a  yellow  tint ;  it  fuses  when  exposed  to  a 
higher  degree  of  heat.  When  strongly  ignited,  it  suffers  a  slight 
diminution  of  weight,  losing  a  small  proportion  of  arsenic  acid, 
which  escapes  as  arsenious  oxide  and  oxygen.  In  analysis  we  have 
never  occasion  to  operate  upon  the  pure  lead  arsenate,  but  upon  a 
mixture  of  it  with  lead  oxide. 

1).  A.rsenious  sulphide  forms  a  precipitate  of  a  rich  yellow 
color;  it  is  insoluble  in  water,*  and  also  in  hydrogen  sulphide 
water.  •  When  boiled  with  water,  or  left  for  several  days  in  con- 
tact with  that  fluid,  it  undergoes  a  very  trifling  decomposition :  a 
trace  of  arsenious  acid  dissolves  in  the  water,  and  a  minute  pro- 
portion of  hydrogen  sulphide  is  disengaged.  This  does  not  in  the 
least  interfere,  however,  with  the  washing  of  the  precipitate.  The 
precipitate  may  be  dried  at  100°,  without  decomposition ;  the 
whole  of  the  water  which  it  contains  is  expelled  at  that  tempera- 
ture. When  exposed  to  a  stronger  heat,  it  transitorily  assumes 
a  brownish-red  color,  fuses,  and  finally  rises  in  vapor,  without 
decomposition.  It  dissolves  readily  in  alkalies,  alkali  carbonates, 

*  In  some  experiments  which  I  had  occasion  to  make,  in  the  course  of  an 
analysis  of  the  springs  of  Weilbach  (Chemische  Untersuchung  der  wichtigsten 
Nassauischen  Mineralwasser  von  Dr.  Fresenius,  V.  Schwefelquelle  zu  Weilbach. 
Weisbaden,  Kreidel  und  Niedner.  1856),  I  found  that  one  part  of  As2Sa  dis- 
solves in  about  one  million  parts  of  water. 


§  92.]  METALS    OF   GROUP   VI.  191 

alkali  sulphides,  potassium  hydrogen  sulphite,  and  nitrohydro- 
chloric  acid ;  but  it  is  scarcely  soluble  in  boiling  concentrated 
hydrochloric  acid.  Hed  fuming  nitric  acid  converts  it  into  arsenic 
acid  and  sulphuric  acid.  It  is  insoluble  in  carbon  disulphide. 

COMPOSITION. 

Asa 150  60-98 

S,  ,  96  39-02 


246  100-00 

c.  Ammonium  magnesium  ar senate  forms  a  white,  somewhat 
transparent,  finely  crystalline  precipitate,  which  when  dried  in  a 
desiccator  has  the  formula  NH4MgAsO4  +  6H2O.  After  drying 
at  100°,  its  composition  is  (NH4MgAsO4)2  +  H2O.  At  a  higher 
temperature,  say  105° — 110°,  more  water  escapes,  and  at  130°  this 
loss  is  considerable  (PULLER*).  Upon  ignition  it  loses  water  and 
ammonia,  and  changes  to  magnesium  pyroarsenate,  Mg3As2O7.  On 
rapid  ignition  the  escaping  ammonia  has  a  reducing  action  on  the 
arsenic  acid,  and  a  notable  loss  is  occasioned  (H.  EOSE)  ;  by  raising 
the  heat  very  gradually  reduction  may  be  avoided  (H.  11 
WrrrsTEiMjt  PULLER),  or  by  passing  a  current  of  dry  oxygen 
during  the  ignition.  Ammonium  magnesium  arsenate  dissolves 
very  sparingly  in  water,  one  part  of  the  salt  dried  at  100°,  requir- 
ing 2656,  one  part  of  the  anhydrous  salt,  2788  parts  of  water  of 
15°.  It  is  far  less  soluble  in  ammoniated  water,  one  part  of  the 
salt  dried  at  100°  requiring  15038,  one  part  of  the  anhydrous  salt, 
15T86  parts  of  a  mixture  of  one  part  of  solution  of  ammonia 
('96  sp.  gr.),  and  3  parts  of  water  at  15°.  In  water  containing 
ammonium  chloride,  it  is  much  more  readily  soluble,  one  part  of 
the  anhydrous  salt  requiring  886  parts  of  a  solution  of  one  part  of 
ammonium  chloride  in  7  parts  of  water.  Presence  of  ammonia 
diminishes  the  solvent  capacity  of  the  ammonium  chloride ;  one 
part  of  the  anhydrous  salt  requires  3014  parts  of  a  mixture  of 
60  parts  of  water,  10  of  solution  of  ammonia  (-96  sp.  gr.)  and 
one  of  ammonium  chloride.^  A  solution  of  ammonium  chloride, 
ammonia  and  magnesium  sulphate  dissolves  much  less  of  the  salt 
than  ammoniated  water;  thus,  PULLER  (loc.  cit.)  found  that  one 

*  Zeitschr.  f.  anal.  Chera.  10,  62.  f  Ib.  2,  19. 

$  Zeitschr.  f.  anal.  Chem.  3,  206.     PULLER  obtained  almost  the  same  numbers 
(Ib.  10,  53). 


192  FORMS.  [§92. 

part  of  the  anhydrous  salt  dissolved  in  32827  parts  of  a  fluid  con- 
taining -^  of  magnesia  mixture  (p.  113).  Excess  of  alkali  arsenate 
still  more  diminishes  the  solubility  of  the  salt  in  water  containing 
ammonia  and  ammonium  chloride  (PULLER). 

V 

COMPOSITION    OF    AMMONIUM    MAGNESIUM    ARSENATE     DRIED    AT     100°. 

2MgO.     .     ,       80-00  21-05 

.     .       52.08  13-68 


/AsO/O        '     \- 
l  AsU<—U  >  M    I 

7 


Ag2O5   .     .     .     230-00  60-53 

H20      .     .     .       18-00  4.74 
+H20 

380-08  100-00 

d.  Magnesium  pyr  oar  senate,  obtained  by  careful  ignition  of 
the  preceding  salt,  is  white,  infusible  by  ignition  in  a  porcelain 
crucible  even  over  the  blowpipe,  but  agglutinating  at  a  still  higher 
temperature,  and  finally  fusing.  After  ignition  in  a  porcelain 
crucible  it  dissolves  readily  in  hydrochloric  acid  :  ammonia  pre- 
cipitates ammonium  magnesium  arsenate  from  the  solution  in  a 
crystalline  form. 

COMPOSITION. 


2MgO     ...       80  25-81 

As2O5      ...     230  74-19 


310  100-00 

e.  Uranyl  pyroarsenate.  —  If  a  solution  of  arsenic  acid  is  mixed 
with  potash  in  slight  excess,  then  with  acetic  acid  to  strongly  acid 
reaction,  and  finally  with  uranyl  acetate,  the  whole  of  the  arsenic 
is  thrown  down  as  UO2HAsO4  +  4H2O.  In  the  presence  of  salts 
of  ammonia  the  precipitate  also  contains  the  whole  of  the  arsenic, 
and  consists  of  UO2NH4AsO4  +  water.  Both  precipitates  are  pale 
yellowish-green,  slimy,  insoluble  in  water,  acetic  acid  and  saline 
solutions,  such  as  ammonium  chloride,  soluble  in  mineral  acids. 
Boiling  favors  the  separation  of  the  precipitate,  addition  of  a  few 
drops  of  chloroform  will  help  it  to  settle,  the  washing  is  to  be 
effected  by  boiling  up  and  decanting.  Both  precipitates  give 
(UO2)2As2O7  on  ignition.  The  latter  is  a  light  yellow  residue  ;  if 
it  has  turned  greenish  from  the  action  of  reducing  gases,  it  may  be 
restored  to  its  proper  color  by  moistening  with  nitric  acid  and 


§93.]  Anns  OF  GROTP  i.  393 

re-igniting.  On  igniting  the  ammonium  uranyl  arsenate,  the 
ammonia  must  first  be  expelled  by  cautious  heating,  or  a  current  of 
oxygen  must  be  passed  during  the  ignition,  otherwise  the  arsenic 
acid  will  be  partially  reduced,  and  arsenic  will  be  lost  (PULLER*). 


° 


COMPOSITION. 

AsO  <  g  >  1 

JO,          2UOaO  .     . 

571  -  2       71-29 

AsO  <  g  >  1 

TO,          As9O5     .     . 

230-0       28-71 

801-2     100-00 


f.  Arsenic-mol ybdate  of  ammonium. — If  a  fluid  containing 
arsenic  acid  is  mixed  with  excess  of  the  nitric  acid  solution  of 
ammonium  molybdate,  the  fluid  remains  clear  in  the  cold,  but  on 
heating  a  yellow  precipitate  of  arsenio-molybdate  of  ammonium 
separates.  This  precipitate  comports  itself  with  solvents  like  the 
analogous  compound  of  phosphoric  acid ;  it  is,  like  the  latter, 
insoluble  in  water,  nitric  acid,  dilute  sulphuric  acid  and  salts,  pro- 
vided an  excess  of  solution  of  ammonium  molybdate,  mixed  with 
acid  in  moderate  excess,  be  present.  Hydrochloric  acid  or  metallic 
chlorides,  when  present  in  large  quantity,  interfere  with  the 
thoroughness  of  the  precipitation.  SELiasoHNf  found  it  to  be 
composed  of  87*666  per  cent,  of  molybdic  acid,  6*308  arsenic  acid, 
4*258  ammonia,  and  1*768  water. 

R   FORMS  IN  WHICH   THE   ACID  RADICALS  ARE  WEIGHED   OR 

PRECIPITATED. 

ACIDS  OF  THE  FIRST  GROUP. 
§93, 

1.  ARSENIOUS  ACID  and  ARSENIC  ACID. — See  §  92. 

2.  CHROMIC  ACID. 

Chromic  acid  is  weighed  either  as  CHROMIC  OXIDE,  or  as  LEAD 
CHROMATE,  or  BARIUM  CHROMATE.  We  have  also  to  consider  MER- 

CUROUS  CHROMATE. 

a.  Chromic  oxide. — See  §  76. 

b.  Lead  chromate  obtained  by  precipitation  forms  a  bright-yel- 

*  Zeitschr.  f.  anal.  Chem.  10,  72.  f  Journ.  f.  prakt,  ('hem.  67,  481. 


194  FOKMS.  [§  93. 

low  precipitate,  insoluble  in  water  and  acetic  acid,  barely  soluble  in 
dilute  nitric  acid,  readily  in  solution  of  potassa.  When  lead  cliro- 
mate  is  boiled  with  concentrated  hydrochloric  acid,  it  is  readily 
decomposed,  lead  chloride  and  chromic  chloride  being  formed. 
Addition  of  alcohol  tends  to  promote  this  decomposition.  Lead 
chromate  is  unalterable  in  the  air.  It  dries  thoroughly  at  100°. 
Under  the  influence  of  heat  it  transitorily  acquires  a  reddish-brown 
tint  ;  it  fuses  at  a  red  heat  ;  when  heated  beyond  its  point  of 
fusion,  it  loses  oxygen,  and  is  transformed  into  a  mixture  of  chro- 
mic oxide  and  basic  lead  chromate.  Heated  in  contact  with  organic 
substances,  it  readily  yields  oxygen  to  the  latter. 


COMPOSITION. 


223-00     68-94 
100-48     31-06 


323-48  100-00 

c.  Barium  chromate  is  obtained  as  a  light-yellow  precipitate 
on  mixing  a  solution  of  an  alkali  chromate  with  barium  chloride. 
It  dissolves  in  hydrochloric  and  in  nitric  acid,  but  not  in  acetic 
acid.  On  washing  with  pure  water,  the  latter  begins  to  dissolve  it 
slightly,  as  soon  as  all  soluble  salts  are  removed,  to  such  an  extent 
that  the  washings  run  off  yellow.  The  precipitate  is  insoluble  in 
saline  solutions.  Hence  it  is  best  to  use  a  solution  of  ammonium 
acetate  for  washing  (PEARSON  and  RICHARDS*).  It  is  not  decom- 
posed by  moderate  ignition. 

COMPOSITION. 

BaO     -     •     -     153-00  60-36 

100-48  39-64 


253-48  100-00 

d.  Mercurous  chromate  obtained  by  adding  mercurous  nitrate 
to  an  alkali  chromate  is  a  brilliant-red  precipitate,  which  turns 
black  by  the  action  of  light.  It  dissolves  very  slightly  in  cold 
water,  more  in  boiling  water,  being  partially  converted  into  a  mer- 
curic salt ;  it  dissolves  slightly  in  dilute  nitric  acid.  For  washing, 

*Zeitschr.  f.  anal.  Chem.  9,  108. 


§  93.]  ACIDS    OF   GROUP   I.  195 

it  is  best  to  use  a  dilute  solution  of  mercurous  nitrate  containing 
but  little  free  acid ;  in  this  solution  it  is  insoluble  (H.  ROSE*). 

3.  SULPHURIC  ACID. 

Sulphuric  acid  is  determined  best  in  the  form  of  BARIUM  suir 
PHATE,  for  the  properties  of  which  see  §  71. 

4.  PHOSPHORIC  ACID. 

The  principal  forms  into  which  phosphoric  acid  is  converted  are 
as  follows  : — LEAD  PHOSPHATE,  MAGNESIUM  PYROPHOSPHATE,  MAGNE- 
SIUM PHOSPHATE  Mg3(PO4)3,  FERRIC  PHOSPHATE,  URANYL  PYROPHOS- 
PHATE, STANNIC  PHOSPHATE,  and  SILVER  PHOSPHATE.  Besides  these 
compounds,  we  have  to  examine  MERCUROUS  PHOSPHATE  and 

PHOSPHO-MOLYBDATE  OF   AMMONIUM. 

a.  The  lead  phosphate  obtained  in  the  course  of  analysis  is 
rarely  pure,  but  is  generally  mixed  with  free  lead  oxide.     In  this 
mixture  we  have  accordingly  the  normal  lead  phosphate  Pb3(PO4)a ; 
in  the  pure  state,  this  presents  the  appearance  of  a  white  powder;^ 
it  is  insoluble  in  water,  acetic  acid,  and  ammonia.     It  dissolves 
readily  in  nitric  acid.     When  heated  it  fuses  without  decomposi- 
tion. 

b.  Magnesium  pyrophosphate. — See  §  74. 

c.  Magnesium  phosphate  (Mg3(PO4)3). — A  mixture  of  this  com- 
pound with  excess  of  magnesia  is  produced  by  mixing  a  solution  of 
an  alkali  phosphate,  containing  ammonium  chloride,  with  magnesia, 
evaporating,  heating  until  the  ammonium  chloride  is  expelled,  and 
finally  treating  with  water.     It  is  practically  insoluble  in  water  and 
in  solutions  of  salts  of  the  alkalies  (FR.  SCHULZE|). 

d.  Ferric  phosphate. — If  a  solution  of  phosphoric  acid  or  of 
calcium  phosphate  in  acetic  acid  is  carefully  precipitated  with  a 
solution  of  ferric  acetate,  or  with  a     mixture  of  iron-alum  and 
sodium  acetate,  so  that  the  iron  salt  may  just  predominate,  the  pre- 
cipitate always  contains  1  mol.  PaO5  to  1  mol.  Fe2O3  corresponding 
to  the  formula  of  normal  ferric  phosphate,  Fe2(PO4)a  (RAWSKY, 
AViTTSTEiN,  E.  DAVY:):)  ;  if,  on  the  other  hand,  the  ferric  acetate  is 
in  larger  excess,  the  precipitate  is  more  basic.   WITTSTEIN  obtained, 
by  using  a  considerable  -excess  of  ferric  acetate,  a  precipitate  con- 
taining 3P2O5  to  4Fe2O3.     Precipitates  obtained  with  a  small  excess 
of  the  precipitant  possess  a  composition  varying  between  the  above- 

*  Pogg.  Ann.  53,  124.  f  Journ.  f.  prakt.  Chem.  63,  440. 

t  Phil.  Mag.  19,  181. 


196  FORMS.  [§  93o 

mentioned  limits.  RAMMKLSBERG  obtained  Fe2fPO4)2  -|-  4FI2O,  and 
WITTSTEIN  subsequently  the  same  compound  (with  8II0()  instead 
of  4)  upon  mixing  ferric  sulphate  with  sodium  phosphate  in  excess  ; 
with  an  insufficient  quantity  of  sodium  phosphate  the  latter  chem- 
ist obtained  a  more  yellowish  precipitate  which  had  a  composition 
corresponding  to  the  formula -3 Fe2(PO4)2  +  Fea(OH)6+  8H,().  If 
an  acid  fluid  containing  a  considerable  excess  of  phosphoric  acid  is 
mixed  with  a  small  quantity  of  a  ferric  solution,  and  an  alkali 
acetate  is  added,  a  precipitate  of  the  formula,  Fea(PO4)a  -|-  water,  is 
invariably  obtained,  which  accordingly  leaves  upon  ignition  Fea 
(PO4)a  =  FeaO8  -|~  PaO6  (WITTSTEIN).  Fresh  experiments  which 
I  have  made  upon  this  subject  have  convinced  me  of  the  perfect 
correctness  of  this  statement.  MOHR  obtained  the  same  results.* 
The  precipitate  is  insoluble  in  a  fluid  containing  salts,  but  when 
washing,  as  soon  as  the  soluble  salts  are  nearly  removed,  the  pre- 
cipitate begins  to  dissolve.  The  filtrate  has  an  acid  reaction,  and 
contains  iron  and  phosphoric  acid.  The  precipitate,  under  these 
circumstances,  alters  in  composition,  and  this  explains  why  different 
results  were  obtained  in  the  analysis  of  precipitates  which  had  been 
washing  for  different  lengths  of  time  (FR.  MOHR). 

COMPOSITION. 


_P205  ...  142      47-02 
~Fe,O3  .  .  .  160      52-98 
PO---O-  IV 

302 


If  we  dissolve  ferric  phosphate  in  hydrochloric  acid,  supersatu- 
rate the  solution  with  ammonia,  and  apply  heat,  we  obtain  more 
basic  salts,  viz.,  3FeaO,,2PaOB  (RAMMELSBEKG)  ;  2Fe2O3,P2O5  (WITT- 
STEIN — after  long  washing).  In  WITTSTEIN'S  experiment,  the  wash- 
water  contained  phosphoric  acid.  The  white  ferric  phosphate  does 
not  dissolve  in  acetic  acid,  but  it  dissolves  in  a  solution  of  ferric 
acetate.  Upon  boiling  the  latter  solution  (of  ferric  phosphate  in 
ferric  acetate),  the  whole  of  the  phosphoric,  acid  precipitates,  with 
basic  ferric  acetate,  as  hyperbasic  ferric  phosphate.  Similar 
extremely  basic  combinations  are  invariably  obtained  (often  mixed 
with  ferric  hydroxide),  upon  precipitating  with  ammonia  or  barium 

*  Zeitschr.  f.  anal.  Cheni.  2,  250. 


§  93.]  ACIDS   OF   GROUP   I.  197 

carbonate,  a  solution  containing  phosphoric  acid  and  an  excess  of 
a  ferric  salt.  The  precipitate  obtained  by  barium  carbonate  can  be 
conveniently  filtered  off  and  washed,  the  filtrate  is  perfectly  free 
from  either  iron  or  phosphoric  acid  ;  on  the  contrary,  the  precipi- 
tate obtained  by  ammonia,  especially  if  the  latter  were  much  in 
excess,  is  slimy,  and  therefore  difficult  to  wash,  and  the  filtrate 
always  contains  small  traces  of  both  iron  and  phosphoric  acid. 

e.  Uranyl  pyrophosphate. — If  the  hot  aqueous  solution  of  a 
phosphate  soluble  in  water  or  acetic  acid  is  mixed,  in  presence  of 
free  acetic  acid,  with  uranyl  acetate,  a  precipitate  of  uranyl  hydro- 
gen phosphate  is  immediately  formed.  If  the  fluid  contains  much 
ammonium  salt,  the  precipitate  contains  also  uranyl  ammonium 
phosphate.  The  same  precipitate  forms  also  if  aluminium  or  ferric 
salts  are  present;  but  in  that  case  it  is  always  mixed  with  more 
or  less  aluminium  or  ferric  iphosphate.  Presence  of  potassium  or 
sodium  salts,  on  the  contrary,  or  of  salts  of  the  alkali-earth  metals, 
has  no  influence  on  the  composition  of  the  precipitate.  Ammonium 
uranyl  phosphate  (UOay  II4PO4  -f-  #HSO)  is  a  somewhat  gelatinous, 
whitish-yellow  precipitate,  with  a  tinge  of  green.  The  best  way 
of  washing  it,  at  least  so  far  as  the  principal  part  of  the  operation 
is  concerned,  is  by  boiling  with  water  and  decanting.  If,  after 
having  allowed  the  fluid  in  which  the  precipitate  is  suspended  to 
cool  a  little,  a  few  drops  of  chloroform  are  added,  and  the  mixture 
is  shaken  or  boiled  up,  the  precipitate  subsides  much  more  readily 
than  without  this  addition. 

The  precipitate  is  insoluble  in  water  and  in  acetic  acid ;  but  it 
dissolves  in  mineral  acids ;  ammonium  acetate,  added  in  sufficient 
excess,  completely  re-precipitates  it  from  this  solution,  upon  appli- 
cation of  heat.  Upon  igniting  the  precipitate,  no  matter  whether 
containing  ammonium  or  not,  uranyl  pyrophosphate  of  the  for- 
mula (UO2)2P2O7  is  produced.  This  has  the  color  of  the  yolk  of  an 
egg.  If  the  precipitate  is  ignited  in  presence  of  charcoal  or  of  some 
reducing  gas,  partial  reduction  to  uranous  phosphate  ensues,  owing 
to  which  the  ignited  mass  acquires  a  greenish  tint ;  however,  upon 
warming  the  greenish  residue  with  some  nitric  acid,  the  green  ura- 
nous salt  is  readily  reconverted  into  the  yellow  uranyl  salt.  Uranyl 
pyrophosphate  is  not  hygroscopic,  and  may  therefore  be  ignited 
and  weighed  in  an  open  platinum  dish  (A.  AREXDT  and  "W.  KNOP*). 


*  Chemisches  Centralblatt,  1856,  769,  803;  and  1857,  177. 


198  FOEMS.  [§  93. 

PO<9>UOa        2UO2O      .     .571-2          80-09 

°< 

^PO<Q>UO,         PaO5      .     ...142-0  19-91 

713-2         100  00 

The  one-fifth  part  of  the  precipitate  may  accordingly  be  cal- 
culated as  phosphoric  anhydride  in  ordinary  analyses.* 

f.  Stannic  phosphate  is  never  obtained  in  the  pure  state  in  the 
analytical  process,  but  contains  always  an  admixture  of  hydrated 
metastannic  acid  in  excess,  which,  upon  ignition,  changes  to  meta- 
stannic acid.     It  has,  generally  speaking,  the  same  properties  as 
hydrated  metastannic  acid,  and  is  more  particularly,  like  the  latter, 
insoluble  in  nitric  acid.     Upon  heating  with  concentrated  solution 
of  potassa,  potassium  phosphate  and  rnetastannate  are  formed. 

g.  Normal  silver  phosphate  is  a  yellow  powder ;  it  is  insoluble 
in  water,  but  readily  soluble   in  nitric  acid,  and  also  in  ammonia. 
In  ammonium  salts,  it  is  difficultly  soluble.     It  is  unalterable  in 
the  air.      Upon  ignition,  it  acquires  transiently  a  reddish-brown 
color ;  at  an  intense  red  heat,  it  fuses  without  decomposition. 

.  .  695-82     83-05 
142-00     16-95 


837-82    100-00 

h.  Mercurous  phosphate. — This  compound  is  employed  for  the 
purpose  of  effecting  the  separation  of  phosphoric  acid  from  many 
bases,  after  H.  ROSE'S  method. 

Mercurous  phosphate  presents  the  appearance  of  a  white  crys- 
talline mass,  or  of  a  white  powder.  It  is  insoluble  in  water,  but 
dissolves  in  nitric  acid.  The  action  of  a  red  heat  converts  it  into 
fused  mercuric  phosphate,  with  evolution  of  vapor  of  mercury. 
Upon  fusion  with  alkali  carbonates,  alkali  phosphates  are  pro- 
duced, and  mercury,  oxygen,  and  carbon  dioxide  escape. 

i.  Phospho-molybdate   of  ammonium. — This   compound    also 


*  The  atomic  weight  of  uranium  is  here  taken  as  237*6,  according  to  Ebel- 
men.  If  we  take  it  according  to  Peligot,  as  240,  the  ignited  phosphate  would 
contain  80'22  UO3,  and  19*78  P2O6.  W.  Knop  and  Arendt  found  in  four 
experiments  20*13,  20*06,  20*04,  and  20*04  respectively  (in  another  20*77).  It 
will  be  seen  that  these  numbers  agree  better  with  the  composition  as  reckoned 
from  Ebelmen's  than  from  Peligot's  atomic  weight. 


•§  93.]  ACIDS  OF  GROUP  i.  199 

serves   to   effect   the   separation   of   phosphoric   acid  from  other 
bodies ;  it  is  of  the  utmost  importance  in  this  respect. 

Phospho-molybdate  of  ammonium  forms  a  bright  yellow,  readily 
subsiding  precipitate.  Dried  at  100°,  it  has,  according  to  SELIG- 
SOHN,  the  following  (average)  composition  :— 

MoO3 90-744 

P2O5      . 3-142 

CN"H4)fO 3'- 570 

H,O      .     .    ' 2-544 


100-000* 

In  the  pure  state,  it  dissolves  but  sparingly  in  cold  water  (1  in 
10000 — EGGERTZ)  ;  but  it  is  soluble  in  hot  water.  It  is  readily 
soluble  even  in  the  cold,  in  caustic  alkalies,  alkali  carbonates  and 
phosphates,  ammonium  chloride,  and  ammonium  oxalate.  It  dis- 
solves sparingly  in  ammonium  sulphate,  potassium  nitrate,  and 
potassium  chloride ;  and  very  sparingly  in  ammonium  nitrate. 

It  is  soluble  in  potassium  sulphate  and  sodium  sulphate,  sodium 
chloride  and  magnesium  chloride,  and  sulphuric,  hydrochloric  and 
nitric  acids  (concentrated  and  dilute).  Water,  containing  1  per 
cent,  of  common  nitric  acid,  dissolves  ^Vfr  (EGGERTZ).  Appli- 
cation of  heat  does  not  check  the  solvent  action  of  these  substances. 
Presence  of  ammonium  molybdate  totally  changes  its  deportment 
with  acid  fluids.  Dilute  nitric  or  sulphuric  acid  containing 
ammonium  molybdate  does  not  dissolve  it ;  but  much  hydro- 
chloric acid,  even  in  the  presence  of  ammonium  molybdate,  has 
a  solvent  action,  and  this  acid  consequently  interferes  with  the 
complete  precipitation  of  phosphoric  acid  by  nitric  acid  solution 
of  ammonium  molybdate.  The  solution  of  the  phospho-molybdate 
of  ammonium  in  acids  is  probably  attended,  in  all  cases,  with 
decomposition  and  separation  of  the  rnolybdic  acid,  which  cannot 
take  place  in  the  presence  of  ammonium  molybdate  (J.  CRAW)+ . 
Tartaric  acid  and  similar  organic  substances  entirely  prevent  the 

*  From  the  varying  results  of  different  analysts  it  is  plain  that  the  precipi- 
tate, prepared  under  apparently  the  same  circumstances,  has  not  always  exactly 
the  same  composition.  SONNENSCHEIX  (Journ.  f .  prakt.  Chem.  53,  342)  found  in 
the  precipitate  dried  at  120°,  2'93— 3'12  §  P2O5;  LIPOWITZ  (Pogg.  Annal.  109, 
135),  in  the  precipitate  dried  at  from  20°  to  30°,  3'607  £  P2O5;  EGGERTZ  (Journ. 
f.  prakt.  Chem.  79,  496),  3 '7  to  3  "8  $. 

f  Chem.  Gaz.  1852,  216. 


200  FORMS.  [§  93. 

precipitation  of  the  phospho-molybdate  of  ammonium  (EGGERTZ). 
In  the  presence  of  an  iodide  instead  of  a  yellow  precipitate,  a  green 
precipitate  or  a  green  fluid  is  formed,  resulting  from  the  reducing 
action  of  the  hydriodic  acid  on  the  molybdic  acid  (J.  W.  BILL*). 
Other  substances  which  reduce  molybdic  acid  have  of  course  a 
similar  action. 

5.  BORACIC  ACID. 

POTASSIUM  BOROFLUORIDE  is  the  best  form  to  convert  boracic 
acid  into  for  the  purpose  of  the  direct  estimation  of  the  acid.  This 
compound  is  produced  by  mixing  the  solution  of  an  alkali  borate, 
in  presence  of  a  sufficient  quantity  of  potassa,  with  hydrofluoric 
acid  in  excess,  in  a  silver  or  platinum  dish,  and  evaporating  to  dry- 
ness.  The  gelatinous  precipitate  which  forms  in  the  cold,  dissolves 
upon  application  of  heat,  and  separates  from  the  solution  subse- 
quently, upon  evaporation,  in  small,  hard,  transparent  crystals. 
The  compound  has  the  formula  KF,BF3.  It  is  soluble  in  water 
arid  also  in  dilute  alcohol ;  but  strong  alcohol  fails  to  dissolve  it  t* 
it  is  insoluble  also  in  concentrated  solution  of  potassium  acetate. 
It  may  be  dried  at  100°,  without  decomposition  (AuG.  STRO- 

MEYERf). 

COMPOSITION. 

K 39-13  31-02 

B 11-00  8-72 

F 76-00  60-26 

126-13  100-00 

6.  OXALIC  ACID. 

When  oxalic  acid  is  to  be  directly  determined  it  is  usually  pre- 
cipitated in  the  form  of  CALCIUM  OXALATE  ;  and  its  weight  is 
inferred  from  the  CALCIUM  CARBONATE  or  CALCIUM  OXIDE  produced 
from  the  oxalate  by  ignition.  For  the  properties  of  these  bodies 
see  §  73. 

7.  HYDROFLUORIC  ACID. 

The  direct  estimation  of  hydrofluoric  acid  is  usually  effected 
by  weighing  the  acid  in  the  form  of  CALCIUM  FLUORIDE. 

Calcium  fluoride  forms  a  gelatinous  precipitate,  which  it  is 
found  difficult  to  wash.  If  digested  with  ammonia,  previous  to 


*  Sillim.  Journ.,  July,  1858.          \  Annal.  d.  Chem.  u.  Pharm.  100,  82. 


§  93.]  ACIDS    OF   GROUP   I.  201 

filtration,  it  is  rendered  denser  and  less  gelatinous.  It  is  not  alto- 
gether insoluble  in  water ;  aqueous  solutions  of  the  alkalies  fail  to 
decompose  it.  It  is  very  slightly  soluble  in  dilute,  but  more 
readily  in  concentrated  hydrochloric  acid.  When  acted  upon  by 
sulphuric  acid,  it  is  decomposed,  and  calcium  sulphate  and  hydro- 
fluoric acid  are  formed.  Calcium  fluoride  is  unalterable  in  the  air, 
and  at  a  red  heat.  Exposed  to  a  very  intense  heat,  it  fuses.  Upon 
intense  ignition  in  moist  air,  it  is  slowly  and  partially  decomposed 
into  calcium  oxide  and  hydrofluoric  acid.  Mixed  with  ammonium 
chloride,  and  exposed  to  a  red  heat,  calcium  fluoride  suffers  a  con- 
tinual loss  of  weight ;  but  the  decomposition  is  incomplete. 

COMPOSITION. 

Ca     ...!..    40  51-28 

F, 38  48.72 


78  100-00 

We  often  determine  fluorine,  more  particularly  in  presence  of 
silicic  acid,  by  converting  it  into  silicon  fluoride  (SiF4).  This  is  a 
colorless  gas,  fuming  in  the  air,  with  suffocating  odor,  of  sp.  gr. 
3'574,  which  decomposes  when  mixed  with  water  forming  silica 
and  hydrofluosilicic  acid  thus  :  3SiF4  +  2H.O  =  2H2SiF.+  SiO2. 

8.  CARBONIC  Aero. 

The  direct  estimation  of  carbonic  acid — which,  however,  is 
only  rarely  resorted  to — is  usually  effected  by  weighing  the  acid  in 
the  form  of  CALCIUM  CARBONATE.  For  the  properties  of  the  lattefr 
substance,  see  §  73. 

9.  SILICIC  ACID.* 

When  silicic  acid  is  separated  by  acids  from  aqueous  solutions 
of  alkali  silicates,  it  is  at  first  perfectly  soluble  in  water.  It  be- 
comes insoluble  or  rather  difficultly  soluble  when  it  coagulates. 
Coagulation  is  a  permanent  change  and  is  furthered  by  concentra- 
tion and  by  elevation  of  temperature.  Silicic  acid  solution  con- 
taining 10  or  12  per  cent,  of  SiO2  coagulates  at  the  ordinary  tem- 
perature in  a  few  hours,  and  immediately  if  heated.  A  solution  of 

*  Free  silicic  acid  in  solution  is  assumed  to  have  the  composition  expressed 
by  the  formula  Si(OH)4.  Silicic  anhydride  (SiO2)  is  usually  called  "silica." 
Compounds  of  SiO3  with  less  water  than  corresponds  to  the  formula  Si(OH)4  = 
SiO2(H3O)2  are  here  called  "  hydrates  of  silica." 


202  FORMS.  [§  93. 

5  per  cent,  may  be  preserved  without  coagulating  for  five  or  six  days, 
one  of  2  per  cent,  for  two  or  three  months,  and  one  of  1  per  cent, 
for  several  years,  and  solutions  containing  ^  per  cent,  or  less  are 
not  appreciably  altered  by  time.  Solid  matter  in  powder  such  as 
graphite,  hastens  coagulation,  alkali  salts  induce  it  rapidly.  Aque- 
ous solutions  of  silicic  acid  may,  on  the  contrary,  be  mixed  with 
hydrochloric  acid,  nitric  acid,  acetic  acid,  tartaric  acid  and  alcohol 
without  coagulating.  The  gelatinous  silicic  acid  produced  by 
coagulation  may  contain  more  or  less  water,  and  it  appears  to  be 
the  more  difficultly  soluble  in  water,  the  less  water  it  contains; 
thus  a  jelly  of  silicic  acid  containing  1  per  cent,  of  silica  (SiO2)  gives 
a  solution  with  cold  water  containing  1  part  of  silica  in  about  5000 
rparts.  a  jelly  of  5  per  cent,  gives  a  solution  containing  1  part  of  silica 
in  about  10000  parts  of  water.  A  jelly  containing  less  water  is  still 
less  soluble,  and  when  the  jelly,  is  dried  up  to  a  gummy  mass  it  is 
barely  soluble  at  all ;  this  is  also  the  case  with  the  pulverulent 
hydrate  of  silica  obtained  in  the  analysis  of  silicates  by  drying  a 
jelly  containing  much  salts  at  100°  (GrRAHAM*).  The  hydrated 
silica  dried  at  100°  dissolves  but  very  slightly  in  acids  (with  the 
exception  of  hydrofluoric  acid) ;  it  dissolves,  however,  in  solutions 
of  fixed  alkalies  and  alkali  carbonates,  especially  on  heating.  Aque- 
ous ammonia  dissolves  the  jelly  in  tolerable  quantity  and  the  dry 
hydrate  in  very  notable  quantity  (PRiBRAM)f.  Regarding  the 
amount  of  water  in  the  hydrate  dried  at  given  temperatures  chem- 
ists do  not  agree.;}; 

On  ignition  all  the  hydrates  pass  into  anhydrous  silica.  As 
the  vapor  escapes  small  particles  of  the  extremely  fine  powder 
are  liable  to  whirl  up.  This  may  be  avoided  by  moistening  the 
hydrate  in  the  crucible  with  water,  evaporating  to  dry  ness  on  a 
water  bath,  and  then  applying  at  first  a  slight  and  then  a  gradu- 
ally increased  heat. 

The  silica  obtained  by  igniting  the  hydrate  appears  in  the 
amorphous  condition,  with  a  sp.  gr.  of  2'2  to  2*3.  It  forms  a 

*  Pogg.  Annal.  123,  529.  f  Zeitschr.  f.  anal.  Chem.  6,  119. 

\  DOVERI  (Annal.  de  Chim.  et  de  Phys.  21,  40;  Annal.  d.  Chem.  u.  Pharm. 
64,  256)  found  in  the  air-dried  hydrate  16'9  to  17*8  I  water;  J.  FUCHS  (Annal. 
d.  Chem.  u.  Pharm.  82, 119  to  123),  9'1  to  9'6;  G.  LIPPERT,  9'28  to  9'95.  DOVERI 
found  in  the  hydrate ' dried  at  100°,  8'3  to  9*4;  J.  FUCHS,  6 '63  to  6'96;  G.  LIP- 
PERT  4-97  to  5'52.  H.  ROSE  (Pogg.  Annal.  108.  1;  Journ.  fur  prakt.  Chem.  81, 
227)  found  in  the  hydrate  obtained  by  digesting  stilbite  with  concentrated 
hydrochloric  acid,  and  dried  at  150°,  4 '85  $  water. 


§  94.]  ACIDS    OF   GROUP   II.  203 

white  powder  insoluble  in  water,  and  acids  (hydrofluoric  excepted), 
soluble  in  solutions  of  the  fixed  alkalies  and  their  carbonates, 
especially  in  the  heat.  Hydrofluoric  acid  readily  dissolves  amor- 
phous silica;  the  solution  leaves  no  residue  on  evaporation  in 
platinum,  if  the  silica  was  pure.  The  amorphous  silica,  when 
heated  with  ammonium  fluoride  in  a  platinum  crucible,  readily 
volatilizes.  The  ignited  amorphous  silica,  exposed  to  the  air, 
eagerly  absorbs  water,  which  it  will  not  give  up  at  from  100°  to 
150°  (H.  HOSE).  The  lower  the  heat  during  ignition  the  more 
hygroscopic  is  the  residue  (SOUCHAY*).  Silica  fuses  at  the  strong- 
est heat ;  the  mass  obtained  being  vitreous  and  amorphous.  Amor- 
phous silica  ignited  with  ammonium  chloride,  at  first  loses  weight, 
and  then,  when  the  ignition  has  rendered  it  denser,  the  weight 
remains  constant. 

The  amorphous  silica  must  be  distinguished  from  the  crystallized 
or  crystalline  variety,  which  occurs  as  rock  crystal,  quartz,  sand,  &c. 
This  has  a  sp.  gr.  of  2*6  (SCHAFFGOTSCH),  and  is  far  more  difficultly, 
and  in  far  less  amount,  dissolved  by  potash  solution  or  solution  of 
fixed  alkali  carbonates ;  it  is  also  more  slowly  attacked  by  hydro- 
fluoric acid,  or  ammonium  fluoride.  Crystallized  silica  is  not  hygro- 
scopic, whether  strongly  or  gently  ignited  (SOUCHAY).  Vegetable 
colors  are  not  changed  either  by  silica  or  its  hydrates. 

COMPOSITION. 

Si 28-00  46-67 

O, 32-00  53-33 


60-00          100-00 

ACID  RADICALS  OF  THE  SECOND  GROUP. 

§94. 
1.  HYDROCHLORIC  ACID. 

Hydrochloric  acid  is  almost  invariably  weighed  in  the  form  of 
SILVER  CHLORIDE — for  the  properties  of  which  see  §  82. 

2.  HYDROBROMIC  Acn>.     * 
Hydrobromic  acid  is  always  weighed  in  the  form  of  SILVER 

BROMIDE. 

*  Zeitschr.  f.  anal.  Chem.  8,  423. 


204  FORMS.  [§  94. 

Silver  bromide,  prepared  in  the  wet  way,  forms  a  yellowish- 
white  precipitate.  It  is  wholly  insoluble  in  water  and  in  nitric 
acid,  tolerably  soluble  in  ammonia,  readily  soluble  in  sodium  thio- 
sulphate  and  potassium  cyanide.  Concentrated  solutions  of  potas- 
sium, sodium,  and  ammonium  chlorides  arid  bromides  dissolve  it  to 
a  very  perceptible  amount,  while  in  very  dilute  solutions  of  these 
salts  it  is  entirely  insoluble.  Traces  only  dissolve  in  the  alkali 
nitrates.  It  dissolves  abundantly  in  a  concentrated  warm  solution 
of  mercuric  nitrate.  On  digestion  with  excess  of  potassium  iodide 
solution  it  is  completely  converted  into  silver  iodide  (FIELD).  On 
ignition  in  a  current  of  chlorine  silver  bromide  is  transformed  into 
chloride ;  on  ignition  in  a  current  of  hydrogen  it  is  converted  into 
metallic  silver.  Exposed  to  the  light  it  gradually  turns  gray,  and 
finally  black.  Under  the  influence  of  heat,  it  fuses  to  a  reddish 
liquid,  which,  upon  cooling,  solidifies  to  a  yellow,  horn-like  mass. 
Brought  into  contact  with  zinc  and  water,  it  is  decomposed  :  a 
spongy  mass  of  metallic  silver  forms,  and  the  solution  contains  zinc 
bromide. 

COMPOSITION. 

Ag     .     .     .     .     107-93  57-45 

Br  79-95  42-55 


187-88  100-00 

3.  HYDRIODIC  ACID. 

Hydriodic  acid  is  usually  determined  in  the  form  of  SILVER 
IODIDE,  and  occasionally  also  in  that  of  PALLADIOUS  IODIDE. 

a.  Silver  iodide,  produced  in  the  wet  way,  forms  a  light-yellow 
precipitate,  insoluble  in  water,  and  in  dilute  nitric  acid,"  and  very 
slightly  soluble  in  ammonia.  One  part  dissolves,  according  to 
WALLACE  and  LAMONT*  in  2493  parts  of  aqueous  ammonia  sp.  gr. 
•89,  according  to  MARTINI,  in  2510  parts  of  *96  sp.  gr.  It  is  copi- 
ously taken  up  by  concentrated  solution  of  potassium  iodide,  but  it 
is  insoluble  in  very  dilute ;  it  dissolves  readily  in  sodium  thiosul- 
phate  and  in  potassium  cyanide ;  traces  only  are  dissolved  by  alkali 
nitrates.  In  concentrated  warm  solution  of  mercuric  nitrate  it  is- 
copiously  soluble.  Hot  concentrated  nitric  and  sulphuric  acids 
convert  it,  but  with  some  difficulty,  into  silver  nitrate  and  sulphate 
respectively,  with  expulsion  of  the  iodine.  Silver  iodide  acquires  a 


Chem   Gaz.  1859,  137. 


§  94.]  ACIDS    OF   GROUP   II.  205 

black  color  when  exposed^  to  the  light.  When  heated,  it  fuses 
without  decomposition  to  a  reddish  fluid,  which,  upon  cooling, 
solidifies  to  a  yellow  mass,  that  may  be  cut  with  a  knife.  Under 
the  influence  of  excess  of  chlorine  in  the  heat  it  is  completely  con- 
verted into  silver  chloride;  ignition  in  hydrogen  reduces  it  but 
incompletely  to  the  metallic  state.  When  brought  into  contact 
with  zinc  and  water,  it  is  decomposed  but  incompletely :  zinc  iodide 
is  formed,  and  metallic  silver  separates. 

COMPOSITION. 

Ag    .     .     .     .     107-93  45-  97 

I  126-85  54-03 


234-78  100-00 

1.  Palladious  iodide,  produced  by  mixing  an  alkali  iodide 
with  palladious  chloride,  is  a  deep  brownish-black,  flocculent  pre- 
cipitate, insoluble  in  water,  and  in  dilute  hydrochloric  acid,  but 
slightly  soluble  in  saline  solutions  (sodium  chloride,  magnesium 
chloride,  calcium  chloride,  &c.).  It  is  unalterable  in  the  air.  Dried 
simply  in  the  air  it  retains  one  molecule  of  water =5-05  per  cent. 
Dried  long  in  vaciw,  or  at  a  rather  high  temperature  (70°  to  80°), 
it  yields  the  whole  of  this  water,  without  the  least  loss  of  iodine. 
Dried  at  100°,  it  loses  a  trace  of  iodine ;  at  from  300°  to  400°,  the 
whole  of  the  iodine  is  expelled.  It  may  be  washed  with  hot  water, 
without  loss  of  iodine. 

COMPOSITION. 

Pd 106-58  29-58 

I, 253-70  70-42 


360-28  100-00 

4.  HYDROCYANIC  Aero. 

Hydrocyanic  acid,  if  determined  gravimetrically  and  directly,  is 
always  converted  into  SILVEK  CYANIDE — for  the  properties  of  which 
compound  see  §  82. 

5.  HYDROSULPHURIC  ACID. 

The  forms  into  which  the  sulphur  in  hydrogen  sulphide  or 
metallic  sulphides,  is  converted  for  the  purpose  of  being  weighed, 


206  FORMS.  [§  95. 

are  ARSENIOUS  SULPHIDE,  SILVER  SULPHIDE,  COPPER  SULPHIDE,  and 

BARIUM  SULPHATE. 

For  the  properties  of  the  sulphides  named,  see  §§  82,  85,  92 ; 
for  those  of  barium  sulphate,  see  §  71. 

ACID  RADICALS  OF  THE  THIRD  GROUP. 

§95. 
1.  NITRIC  ACID  ;  and  2.  CHLORIC  Aero. 

These  two  acids  are  never  determined  directly — that  is  to  say, 
in  compounds  containing  them,  but  always  in  an  indirect  way ; 
generally  volumetrically. 


SECTION    IV. 

THE   DETERMINATION   (OR  ESTIMATION)  OF 
RADICALS. 

§96. 

IN  the  preceding  Section  we  have  examined  the  composition 
and  properties  of  the  various  forms  and  combinations  in  which 
radicals  are  separated  from  each  other,  or  in  which  they  are  weighed. 
We  have  now  to  consider  the  special  means  and  methods  of  con- 
verting them  into  such  forms  and  combinations. 

For  the  sake  of  greater  clearness  and  simplicity,  we  shall,  in 
the  present  Section,  confine  our  attention  to  the  various  methods 
applied  to  effect  the  determination  of  single  radicals,  deferring  to 
the  next  Section  the  consideration  of  the  means  adopted  for  sepa- 
rating them  from  each  other. 

As  in  the  "  Qualitative  Analysis,"  the  acids  of  arsenic  will  be 
treated  of  among  the  bases,  on  account  of  their  behavior  to  hydro- 
gen sulphide. 

In  the  quantitative  analysis  of  a  compound  we  have  to  study 
first,  the  most  appropriate  method  of  dissolving  it ;  and,  secondly, 
the 'modes  of  determining  the  quantity  of  one  or  more  of  its  cqn- 
stituents. 

With  regard  to  the  latter  point,  we  have  to  turn  our  attention, 
first,  to  the  performance;  and  secondly,  to  the  accuracy  of  the 
methods. 

It  happens  very  rarely  in  quantitative  analyses  that  the  amount 
of  a  substance,  as  determined  by  the  analytical  process,  corresponds 
exactly  with  the  amount  theoretically  calculated  or  actually  pres- 
ent ;  and  if  it  does  happen,  it  is  merely  by  chance. 

It  is  of  importance  to  inquire  what  is  the  reason  of  this  fact, 
and  what  are  the  limits  of  inaccuracy  in  the  several  methods. 

The  cause  of  this  almost  invariably  occurring  discrepancy 
between  the  quantity  present  and  that  actually  found,  is  to  be 
ascribed  either  exclusively  to  the  twcution*  or  it  lies  partly  in  the 
method  itself. 


208  DETERMINATION.  [§  96. 

The  execution  of  the  analytical  processes  and  operations  can 
never  be  absolutely  accurate,  even  though  the  greatest  care  and 
.attention  be  bestowed  on  the  most  trifling  minutiae.  To  account 
for  this,  we  need  only  bear  in  mind  that  our  weights  and  measures 
are  never  absolutely  correct,  nor  our  balances  absolutely  accurate, 
nor  our  reagents  absolutely  pure ;  and,  moreover,  that  we  do  not 
weigh  m  vacuo  ;  and  that,  even  if  we  deduce  the  weight  in  vacuo 
from  the  weight  we  actually  obtain  by  weighing  in  the  air,  the 
very  volumes  on  which  the  calculation  is  based  are  but  approxi- 
mately known ; — that  the  hygroscopic  state  of  the  air  is  liable  to 
vary  between  the  weighing  of  the  empty  crucible  and  of  the  cru- 
cible -j-  the  substance ; — that  we  know  the  weight  of  a  filter  ash 
only  approximately  y — .that  we  can  never  succeed  in  completely 
keeping  off  dust,  &c. 

With  regard  to  the  methods,  many  of  them  are  not  entirely 
free  from  certain  unavoidable  sources  of  error ; — precipitates  are 
not  absolutely  insoluble;  compounds  which  require  ignition  are 
not  absolutely  fixed ;  others,  which  require  drying,  have  a  slight 
tendency  to  volatilize ;  the  final  reaction  in  volumetric  analyses  is 
usually  pi'oduced  only  by  a  small  excess  of  the  standard  fluid, 
which  is  occasionally  liable  to  vary  with  the  degree  of  dilution,  the 
temperature,  <fec. 

Strictly  speaking,  no  method  can  be  pronounced  quite  free 
from  defect;  it  should  be  borne  in  mind,  for  example,  that  even 
barium  sulphate  is  not  absolutely  insoluble  in  water.  Whenever 
w^e  describe  any  method  as  free  from  sources  of  error,  we  mean, 
fhat  no  causes  of  considerable  inaccuracy  are  inherent  in  it. 

We  have,  therefore,  in  our  analytical  processes,  invariably  to 
contend  against  certain  sources  of  inaccuracy  which  it  is  impossi- 
ble to  overcome  entirely,  even  though  our  operations  be  conducted 
with  the  most  scrupulous  care  and  with  the  utmost  attention  to 
established  rules.  It  will  be  readily  understood  that  several  defects 
and  sources  of  error  may,  in  some  cases,  combine  to  vitiate  the 
results ;  whereas,  in  other  cases,  they  may  compensate  one  another, 
and  thus  enable  us  to  attain  a  higher  degree  of  accuracy.  The 
comparative  accuracy  of  the  results  attainable  by  an  analytical 
method  oscillates  between  two  points — these  points  are  called  the 
limits  of  error.  In  the  case  of  methods  free  from  sources  of  error, 
these  limits  will  closely  approach  each  other ;  thus,  for  instance,  in 


§  96.]  DETERMINATION.  209 

the  determination  of  chlorine,  with  great  care  one  will  always  be 
able  to  obtain  between  99'9  and  lOO'l  for  the  100  parts  of  chlorine 
actually  present. 

Less  perfect  methods  will,  of  course,  exhibit  far  greater  dis- 
crepancies ;  thus,  in  the  estimation  of  strontium  by  means  of  sul- 
phuric acid,  the  most  attentive  and  skilful  operator  may  not  be 
able  to  obtain  more  than  99*0  (and  even  less)  for  the  100  parts 
of  strontium  actually  present.  I  may  here  incidentally  state  that 
the  numbers  occasionally  given  in  this  manner,  in  the  course  of  the 
present  work,  to  denote  the  degree  of  accuracy  of  certain  methods, 
refer  invariably  to  the.  substance  estimated  (chlorine,  nitrogen, 
baryta,  for  instance),  and  not  to  the  combination  in  which  that 
substance  may  be  weighed  (silver  chloride,  ammonium  platinic 
chloride,  barium  sulphate,  for  instance) ;  otherwise  the  accuracy  of 
various  methods  would  not  be  comparable. 

The  occasional  attainment  of  results  exactly  corresponding  with 
the  numbers  calculated  does  not  always  justify  the  assumption,  on 
the  part  of  the  student,  that  his  operations,  to  have  led  to  such  a 
result,  must  have  been  conducted  with  the  utmost  precision  and 
accuracy.  It  may  sometimes  happen,  in  the  course  of  the  analyti- 
cal process,  that  one  error  serves  to  compensate  another ;  thus,  for 
instance,  the  analyst  may,  at  the  commencement  of  his  operations, 
spill  a  minute  portion  of  the  substance  to  be  analyzed ;  whilst,  at  a 
later  stage  of  the  process,  he  may  recover  the  loss  by  an  imperfect 
washing  of  the  precipitate.  As  a  general  rule,  results  showing  a 
trifling  deficiency  of  substance  may  be  looked  upon  as  better  proof 
of  accurate  performance  of  the  analytical  process  than  results 
exhibiting  an  excess  of  substance. 

As  not  the  least  effective  means  of  guarding  against  error  and 
inaccuracies  in  gravimetric  analyses,  I  would  most  strongly  recom- 
mend the  analyst,  after  weighing  a  precipitate,  dec.,  to  compare 
its  properties  (color,  solubility,  reaction,  dec.)  with  those  which  it 
should  possess,  and  which  have  been  amply  described  in  the  pre- 
ceding Section. 

In  my  own  laboratory,  I  insist  upon  all  substances  that  are 
weighed  in  the  course  of  an  analysis  being  kept  between  watch- 
glasses,  until  the  whole  affair  is  concluded.  This  affords  always  a 
chance  of  testing  them  once  more  for  some  impurity,  the  presence 
of  which  may  become  suspected  in  the  after-course  of  the  process. 


210  DETERMINATION.  [§  97. 

I.   DETERMINATION  OF  BASIC  RADICALS  IN  SIMPLE  SALTS. 

First  Group. 

POTASSIUM SODIUM AMMONIUM (LITHIUM). 

§97. 

1.  POTASSIUM. 

a.  Solution. 

Potassa  and  potassium  salts  of  those  inorganic  acids  which  we 
have  to  consider  here,  are  dissolved  in  water,  in  which  menstruum 
they  dissolve  readily,  or  at  all  events,  pretty  readily. 

Potassium  salts  of  organic  acids  it  is  most  convenient  to  convert 
into  potassium  sulphate.  See  p.  211. 

b.  Determination. 

Potassium  is  weighed  either  as  potassium  sulphate,  as  potassium 
chloride,  or  as  potassium  platinic  chloride  (see  §  68).  It  may  also 
be  determined  volumetrically.  For  the  alkalimetric  estimation  of 
potassa  or  potassium  carbonate,  see  §§  195  and  196. 

We  may  convert  into 

1.  POTASSIUM  SULPHATE. 

Potassium  salts  of  strong  volatile  acids ;  e.g.,  potassium  chloride, 
potassium  bromide,  potassium  nitrate,  &c.,  and  salts  of  organic 
acids. 

2.  POTASSIUM  CHLORIDE. 

In  general,  caustic  potassa  and  potassium  salts  of  weak  volatile 
acids;  also,  and  more  particularly,  potassium  sulphate,  chromate, 
chlorate,  and  silicate. 

3.  POTASSIUM  PLATINIC  CHLORIDE. 

Potassium  salts  of  non-volatile  acids  soluble  in  alcohol;  e.g., 
potassium  phosphate,  potassium  berate. 

The  potassium  in  potassium  borate  may  be  determined  also  as 
sulphate  (§  136) ;  and  the  potassium  in  the  phosphate,  as  potassium 
chloride  (§  135). 

The  form  of  potassium  platinic  chloride  may  also  be  resorted 
to  in  general,  for  the  estimation  of  potassium  in  all  potassium  salts 
of  those  acids  which  are  soluble  in  alcohol.  This  form  is,  more- 
over, of  especial  importance,  as  that  in  which  the  separation  of 
potassium  from  sodium,  &c.,  is  effected. 


§  97.]  POTASSIUM.  211 

4.  POTASSIUM  SILICOFLTJOKIDE. 

Potassium  salts  of  those  acids  which  are  soluble  in  weak  alcohol, 
except  borate. 

1.  Determination  as  Potassium  Sulphate. 

Evaporate  the  aqueous  solution  of  the  potassium  sulphate  to 
dryness,  ignite  the  residue  in  a  platinum  crucible  or  dish,  and 
.weigh  (§  42).  The  residue  must  be  thoroughly  dried  before  you 
proceed  to  ignite  it ;  the  heat  applied  for  the  latter  purpose  must 
be .  moderate  at  first,  and  very  gradually  increased  to  the  requisite 
degree  ;  the  crucible  or  dish  must  be  kept  well  covered — neglect  of 
these  precautionary  rules  involves  always  a  loss  of  substance  from 
decrepitation.  If  free  sulphuric  acid  is  present,  we  obtain,  upon 
evaporation,  acid  potassium  sulphate ;  in  such  cases  the  acid  salt  is 
to  be  converted  into  the  normal  by  igniting  first  alone  (here  it  is 
best  to  place  the  lamp  so  that  the  flame  may  strike  the  dish-cover 
obliquely  from  above),  then  with  ammonium  carbonate.  See  §  68. 

For  properties  of  the  residue,  see  §  68.  Observe  more  particu- 
larly that  the  residue  must  dissolve  to  a  clear  fluid,  and  that  the 
solution  must  be  neutral.  Should  traces  of  platinum  remain  behind 
(the  dish  not  having  been  previously  weighed),  these  must  be  care- 
fully determined,  and  their  weight  subtracted  from  that  of  the 
ignited  residue. 

With  proper  care  and  attention,  this  method  gives  accurate 
results. 

To  convert,  the  above-mentioned  salts  (potassium  chloride,  &c.) 
into  potassium  sulphate,  add  to  their  aqueous  solution  a  quantity 
of  pure  sulphuric  acid  more  than  sufficient  to  form  normal  sulphate 
with  the  whole  of  the  potassium,  evaporate  the  solution  to  dry- 
ness,  ignite  the  residue,  and  convert  the  resulting  acid  potassium 
sulphate  into  the  normal,  by  treating  with  ammonium  carbonate 
(§68). 

As  the  expulsion  of  a  large  quantity  of  sulphuric  acid  is  a  very 
disagreeable  process,  avoid  adding  too  great  an  excess.  Should  too 
little  of  the  acid  have  been  used,  which  you  may  infer  from  the 
non-evolution  of  sulphuric  acid  fumes  on  ignition,  moisten  the 
residue  with  dilute  sulphuric  acid,  evaporate,  and  again  ignite.  If 
you  have  to  deal  with  a  small  quantity  only  of  potassium  chloride, 
&c.,  proceed  at  once  to  treat  the  dry  salt,  cautiously,  with  dilute 
sulphuric  acid  in  the  platinum  crucible ;  provided  the  latter  be 


212  DETERMINATION.  [§  97. 

capacious  enough.     In  the  case  of  potassium  bromide  and  iodide, 
the  use  of  platinum  vessels  must  be  avoided. 

[Potassium  salts  of  organic  acids  are  directly  converted  into 
potassium  sulphate  by  first  carbonizing  them  at  the  lowest  possible 
temperature,  and  after  cooling  adding  some  crystals  of  pure  ammo- 
nium sulphate  and  a  little  water  to  the  mass.  The  crucible  being 
covered,  the  water  is  evaporated  by  heating  the  crucible  cover,  and 
the  whole  is  afterwards  heated  to  dull  redness,  until  the  excess  of . 
ammonium  sulphate  is  destroyed.  If  the  carbon  is  not  fully  con- 
sumed by  this  operation,  add  a  little  ammonium  nitrate  and  repeat 
the  ignition.  Kammerer.*]  It  is  usually  advisable  to  ignite  finally 
in  an  atmosphere  of  ammonium  carbonate. 

2.  Determination  as  Potassium  Chlan'de. 

General  method  the  same  as  described  in  1.  The  residue  of 
potassium  chloride  must,  previously  to  ignition,  be  treated  in  the 
same  way  as  potassium  sulphate,  and  for  the  same  reason.  The 
salt  must  be  heated  in  a  well-covered  crucible  or  dish,  and  only  to 
dull  redness,  as  the  application  of  a  higher  degree  of  heat  is  likely 
to  cause  some  loss  by  volatilization.  No  particular  regard  need  be 
had  to  the  presence  of  free  acid.  For  properties  of  the  residue, 
see  §  68.  This  method,  if  properly  and  carefully  executed,  gives 
very  accurate  results.  The  potassium  chloride  may,  instead  of 
being  weighed,  be  determined  volumetrically  by  §  141,  b.  This 
method,  however,  has  no  advantage  in  the  case  of  single  estima- 
tions, but  saves  time  when  a  series  of  estimations  has  to  be 
made. 

In  determining  potassium  in  the  carbonate  it  is  sometimes 
desirable  to  avoid  the  effervescence  occasioned  by  treatment  with 
hydrochloric  acid,  as,  for  instance,  in  the  case  of  the  ignited  resi- 
due of  a  potassium  salt  of  an  organic  acid,  which  is  contained  in 
the  crucible.  This  may  be  effected  by  treating  the  carbonate  with 
solution  of  ammonium  chloride  in  excess,  evaporating  and  igniting, 
when  ammonium  carbonate  and  the  excess  of  ammonium  chloride 
will  escape,  leaving  potassium  chloride  behind. 

The  methods  of  converting  the  potassium  compounds  specified 
above  into  pqtassium  chloride,  will  be  found  in  Part  II.  of  this 
Section,  under  the  respective  heads  of  the  acids  which  they  con- 
tain. 


[*  Fres.  Zeit.  VII.  222.] 


§  97.]  POTASSIUM.  213 

3.  Determination  a#  Potassium  Platinic  Chloride. 

a.  Potassium  salts  of  volatile  acids  (nitric  acid,  acetic  acid,  &c.). 

Mix  the  solution  with  hydrochloric  acid,  evaporate  to  dryness, 
dissolve  the  residue  in  a  little  water,  add  a  concentrated  solution 
of  platinic  chloride,  as  neutral  as  possible,  in  excess,  and  evaporate 
in  a  porcelain  dish,  on  the  water-bath,  nearly  to  dryness,  taking 
care  not  to  heat  the  water-bath  quite  to  boiling.  Add  alcohol  of 
about  80  per  cent,  by  volume  to  the  residue  and  let  it  stand  for 
some  time,  pour  the  alcoholic  solution  through  a  small  filter,  and 
treat  the  residue  if  necessary  a  few  times  with  small  quantities  of 
alcohol  of  the  same  strength,  until  it  appears  to  be  pure  potassium 
platinic  chloride.  Bring  this  upon  the  filter  and  wash  completely 
by  applying  repeatedly  small  quantities  of  the  same  alcohol.  Dry 
next  the  filter  and  its  contents  in  the  funnel,  for  it  is  necessary 
that  the  alcohol  should  be  completely  volatilized.  Transfer  the 
contents  of  the  filter  carefully  to  a  watch-glass,  and  place  the  filter 
back  into  the  funnel  and  dissolve  and  wash  out  the  small  quantity 
of  adhering  potassium  platinic  chloride  with  hot  water.  Evaporate 
the  yellow  solution  thus  obtained  to  dryness  in  a  weighed  platinum 
vessel.  Then  bring  the  chief  quantity  of  the  precipitate  into  the 
platinum  dish  and  dry  the  whole  to  a  constant  weight  at  130°  C. 

If  the  quantity  of  potassium  platinic  chloride  obtained  is  very 
small,  the  whole  may  be  dissolved  from  the  filter,  evaporated  and 
dried  in  the  same  manner.* 

ft.  Potassium  salts  of  non-volatile  acids  (phosphoric  acid,  bora- 
cic  acid,  «fcc.). 

Make  a  concentrated  solution  of  the  salt  in  water,  add  some 
hydrochloric  acid,  and  platinic  chloride  in  excess,  mix  with  a 
tolerable  quantity  of  the  strongest  alcohol,  let  the  mixture  stand 
24  hours  ;  after  which  filter,  and  proceed  as  directed  in  a. 

Properties  of  the  precipitate,  §  68.  This  method,  if  properly 
executed,  gives  satisfactory  results.  Still  there  is  generally  a 
trifling  loss  of  substance,  potassium  platinic  chloride  not  being 
absolutely  insoluble  even  in  strong  alcohol.  In  accurate  analyses, 
therefore,  the  alcoholic  washings  must  be  evaporated,  with  addi- 
tion of  a  little  pure  sodium  chloride,  at  a  temperature  not  exceed- 
ing 75°,  nearly  to  dryness,  and  the  residue  treated  once  more  with 

*  When  many  successive  determinations  are  to  be  made,  especially  in 
technical  analyses,  much  time  can  be  saved  by  using  GOOCH'S  apparatus  (see 
p.  100)  for  washing  and  weighing  the  K2PtCl6. 


214  DETERMINATION.  [§  97. 

alcohol  of  80  per  cent.  A  trifling  additional  amount  of  potassium 
platinic  chloride  is  thus  obtained,  which  is  either  added  to  the 
principal  precipitate  or  collected  on  a  separate  small  filter,  and 
weighed  by  dissolving  from  the  filter  and  evaporating  to  dryness 
as  above  described.  The  object  of  the  addition  of  a  little  sodium 
chloride  to  the  platinic  chloride  is  to  obviate  the  decomposition 
to  which  pure  platinic  chloride  is  more  liable,  upon  evaporation  in 
alcoholic  solution  alone,  than  it  is  when  mixed  with  sodium  pla- 
tinic chloride.  The  atmosphere  of  a  laboratory  often  contains 
ammonia,  which  might  give  rise  to  the  formation  of  some  am- 
monium platinic  chloride,  and  to  a  consequent  increase  of  weight 
in  the  potassium  salt. 

4.  Volumetric  determination  after  conversion  into  Potas- 
sium Silicofluoride. 

To  the  moderately  concentrated  solution  of  the  potassium  salt 
in  a  beaker  add  a  sufficiency  of  hydrofluosilicic  acid,*  and  then  an 
equal  volume  of  pure  strong  alcohol.  If  the  potassium  salt  was 
difficultly  soluble  (such  as  potassium  platinic  chloride),  warm  it 
with  the  hydrofluosilicic  acid  before  adding  the  spirit.  The  potas- 
sium silicofluoride  will  separate  as  a  translucent  precipitate  ;  when 
it  has  settled,  filter,  wash  out  the  beaker  with  a  mixture  of  equal 
parts  strong  alcohol  and  water,  and  wash  the  precipitate  with 
the  same  mixture  till  th6  washings  are  no  longer  acid  to  litmus 
paper.  Put  the  filter  and  precipitate  into  the  beaker  previously 
-used,  treat  with  water,  add  some  tincture  of  litmus,  heat  to  boil- 
ing, and  add  standard  potash  solution  (§  192)  till  the  fluid  is  just 
blue,  and  remains  so  after  continued  boiling.  The  reaction  is  as 
follows  :  (KF)3SiF,  +  4KOH  =  6KF  +  Si(OH)4,  consequently 
2  atoms  potassium  in  the  standard  solution  correspond  to  1  at. 
potassium  originally  present  and  precipitated  as  potassium  silico- 
fluoride (PR.  STOLBAf). 

If  the  solution  of  the  potassium  salt  contains  much  free  acid, 
particularly  sulphuric  acid,  this  is  to  be  removed  by  heat  before 
adding  the  hyrofluosilicic  acid.  Small  quantities  of  ammonium 
salts  are  of  no  influence,  large  quantities  should  be  removed. 
It  need  hardly  be  mentioned  that  other  metals  precipitable  by 


*  W.  KNOP  and  W.  WOLF  use  hydrofluosilicate  of  aniline  instead. — Zeit 
schr.  f.  anal.  Chem.  1,  471. 

•f  Zeitschr.  f.  anal.  Chem.  3,  298. 


§  98.  J  SODIUM.  215 

hydrofluosilicic  acid  must  be  absent.  The  results  are  satisfactory. 
STOLBA  obtained  99*2  to  100  per  cent.  Potassium  platinic  chloride 
may  be  easily  converted  into  potassium  silicofluoride ;  hence,  in 
technical  analyses>  the  potassium  may  be  separated  in  the  first 
form,  and  then  titrated  as  the  latter  (STOLBA,  loc.  cit.). 

§98. 

2.  SODIUM. 

a.  Solution. 

See  §  97,  a — solution  of  potassa  sodium — all  the  directions 
given  in  that  place  applying  equally  to  the  solution  of  soda  and 
sodium  salts. 

b.  Determination. 

Sodium  is  determined  either  as  sodium  sulphate,  as  sodium 
chloride,  or  as  sodium  carbonate  (§  69).  For  the  alkalimetric  esti- 
mation of  caustic  soda  and  sodium  carbonate,  see  §§  195  and  196. 

We  may  convert  into 

1.  SODIUM  SULPHATE;  2.  SODIUM  CHLORIDE. 
In  general  the  sodium  salts  corresponding  to  the  potassium 
salts  specified  under  the  analogous  potassium  compounds,  §  97. 

3.  SODIUM  CARBONATE. 

Caustic  soda,  sodium  hydrogen  carbonate,  and  sodium  salts  of 
organic  acids,  also  sodium  nitrate  and  sodium  chloride. 

In  sodium  borate  the  sodium  is  estimated  best  as  sodium  sul- 
phate (§  136) ;  in  the  phosphate,  as  sodium  chloride,  or  sodium 
carbonate  (§  135). 

Sodium  salts  of  organic  acids  are  determined  either,  like  the 
corresponding  potassium  compounds,  as  chloride,  or — by  preference 
— as  carbonate.  (This  latter  method  is  not  so  well  adapted  for 
potassium  salts.)  The  analyst  must  here  bear  in  mind,  that  when 
carbon  acts  on  fusing  sodium  carbonate,  carbon  monoxide  escapes, 
and  caustic  soda  in  not  inconsiderable  quantity  is  formed. 

1.  Determination  as  Sodium  Sulphate. 

If  alone  and  inv  aqueous  solution,  evaporate  to  dryiiess,  ignite 
and  weigh  the  residue  in  a  covered  platinum  crucible  (§  42).  The 
process  does  not  involve  any  risk  of  loss  by  decrepitation,  as  in  the 
case  of  potassium  sulphate.  If  free  sulphuric  acid  happens  to  be 


216  DETERMINATION.  [§  98. 

present,  this  is  removed  in  the  same  way  as  in  the  case  of  potas- 
sium sulphate. 

With  regard  to  the  conversion  of  sodium  chloride,  &c.,  into 
sodium  sulphate,  see  §  97,  &,  1.  For  properties-  of  the  residue,  see 
§  69.  The  method  is  easy,  and  gives  accurate  results. 

2.  Determination  as  Sodium  Chloride. 

Same  method  as  described  in  1.  The  rules  given  and  the 
observations  made  in  §  97,  £>,  2,  apply  equally  here.  For  properties 
of  the  residue,  see  §  69. 

The  methods  of  converting  sodium  sulphate,  chromate,  chlorate, 
and  silicate  into  sodium  chloride,  will  be  found  in  Part  II.  of  this 
Section,  under  the  respective  heads  of  the  acids  which  these  salts 
contain. 

3.  Determination  as  Sodium  Carbonate. 

Evaporate  the  aqueous  solution,  ignite  moderately,  and  weigh. 
The  results  are  perfectly  accurate.  For  properties  of  the  residue, 
see  §  69. 

Caustic  soda  is  converted  into  the  carbonate  by  adding  to  its 
aqueous  solution  ammonium  carbonate  in  excess,  evaporating  at  a 
gentle  heat,  and  igniting  the  residue. 

Sodium  hydrogen  carbonate,  if  in  the  dry  state,  is  converted 
into  the  normal  carbonate  by  ignition.  The  heat  must  be  very 
gradually  increased,  and  the  crucible  kept  well  covered.  If  in 
aqueous  solution,  it  is  evaporated  to  dryness,  in  a  capacious  silver 
or  platinum  dish,  and  the  residue  ignited. 

Sodium  salts  of  organic  acids  are  converted  into  the  carbonate 
by  ignition  in  a  covered  platinum  crucible,  from  which  the  lid  is 
removed  after  a  time.  The  heat  must  be  increased  very  gradually. 
When  the  mass  has  ceased  to  swell,  the  crucible  is  placed  obliquely, 
with  the  lid  leaning  against  it  (see  §  52,  fig.  42),  and  a  dull  red 
heat  applied  until  the  carbon  is  consumed  as  far  as  practicable. 
The  contents  of  the  crucible  are  then  warmed  with  water,  and  the 
fluid  is  filtered  off  from  the  residuary  carbon,  which  is  carefully 
washed.  The  filtrate  and  rinsings  are  evaporated  to  dryness  with 
the  addition  of  a  little  ammonium  carbonate,  and  the  residue  is 
ignited  and  weighed.  The  ammonium  carbonate  is  added,  to  con- 
vert any  caustic  soda  that  may  have  been  formed  into  carbonate. 
The  method,  if  carefully  conducted,  gives  accurate  results ;  how- 
ever, a  small  loss  of  soda  on  carbonization  is  not  to  be  avoided. 


§99.]  AMMOXH.M.  217 

Sodium  nitrate,  or  sodium  chloride,  may  be  converted  into  car- 
bonate, by  adding  to  their  aqueous  solution  perfectly  pure  oxalic 
acid  in  moderate  excess,  and  evaporating  several  times  to  dryness, 
with  repeated  renewal  of  the  water.  All  the  nitric  acid  of  the 
sodium  nitrate  escapes  in  this-  process  (partly  decomposed,  partly 
undecomposed) ;  and  equally  so  all  the  hydrochloric  acid  in  the 
case  of  sodium  chloride.  If  the  residue  is  now  ignited  until  the 
excess  of  oxalic  acid  is  removed,  sodium  carbonate  is  left. 

§99. 

3.  AMMONIUM. 

a.  Solution. 

Ammonia  is  soluble  in  water,  as  are  all  ammonium  salts  of  those 
acids  which  claim  our  attention  here.  It  is  not  always  necessary, 
however,  to  dissolve  ammonium  salts  for  the  purpose  of  determin- 
ing the  amount  of  ammonium  contained  in  them. 

5.  Determination. 

Ammonium  is  weighed,  as  stated  §  TO,  either  in  the  form  of 
ammonium  chloride^  or  in  that  of  ammonium  platinic  chlori'f' . 
Into  these  forms  it  may  be  converted  either  directly  or  Indirectly 
(i.e.,  after  expulsion  as  ammonia,  and  re-combination  with  an  acid). 
Ammonium  is  also  frequently  determined  by  volumetric  analysis, 
and  its  quantity  is  sometimes  inferred,  from  the  volume  of  nitrogen. 

We  convert  directly  into 

1.  AMMONIUM  CHLORIDE. 

Ammonia  gas  and  its  aqueous  solution,  and  also  ammonium  salts 
of  weak  volatile  acids  (ammonium  carbonate,  ammonium  sulphide, 

&c.). 

2.  AMMONIUM  PLATINIC  CHLORIDE. 

Ammonium  salts  of  acids  soluble  in  alcohol,  such  as  ammonium 
sulphate,  ammonium  phosphate,  &c. 

3.  The  methods  based  on  the  EXPULSION  OF  AMMONIA  from 
ammonium  compounds,  and  also  that  of  inferring  the  amount  of 
ammonium  from  the  volume  of  nitrogen  eliminated  in  the  dry 
way,  are  equally  applicable  to  all  ammonium  salts. 

The  expulsion  of  ammonia  in  the  dry  way  (by  ignition  witli 
soda-lime),  and  its  estimation  from  the  volume  of  nitrogen  elimi- 
nated in  the  dry  way,  being  effected  in  the  same  manner  as  the 


218  DETERMINATION.  [§  99. 

estimation  of  the  nitrogen  in  organic  compounds,  I  refer  the  stu- 
dent to  the  Section  on  organic  analysis.  Here  I  shall  only  give  the 
methods  based  upon  the  expulsion  of  ammonia  and  of  nitrogen  in 
the  wet  way.  For  the  alkalinietric  estimation  of  free  ammonia, 
see  §§  195  and  196. 

1.  Determination  as  Ammonium  Chloride. 
Evaporate  the   aqueous    solution   of  the   ammonium   chloride 

on  the  w^ater-bath,  and  dry  the  residue  at  100°  until  the  weight 
remains  constant  (§  4-2).  The  results  are  accurate.  The  volatili- 
zation of  the  chloride  is  very  trifling.  A  direct  experiment  gave 
99-94  instead  of  100.  (See  Expt.  15.)  The  presence  of  free 
hydrochloric  acid  makes  no  difference ;  the  conversion  of  caustic 
ammonia  into  ammonium  chloride  may  accordingly  be  effected  by 
supersaturating  with  hydrochloric  acid.  The  same  applies  to  the 
conversion  of  the  carbonate,  with  this  addition  only,  that  the  process 
of  supersaturation  must  be  conducted  in  an  obliquely-placed  flask, 
and  the  mixture  heated  in  the  same,  till  the  carbonic  acid  is  driven 
off.  In  the  analysis  of  ammonium  sulphide  we  proceed  in  the 
same  way,  taking  care  simply,  after  the  expulsion  of  the  hydrogen 
sulphide,  and  before  proceeding  to  evaporate,  to  filter  off  the  sul- 
phur which  may  have  separated.  Instead  of  weighing  the  ammo- 
nium chloride,  its  quantity  may  be  inferred  by  the  determination 
of  its  chlorine  according  to  §  14-1,  n.  (Coinp.  potassium  chloride, 
§  97,  5,  3.) 

2.  Determination,  as  Ammonium  Platinic  Chloride, 
a.   Ammoniacal  salts  with  volatile  acids. 

Same  method  as  described  in  §  97,  b,  3,  a  (potassium  platiiiic 
chloride). 

ft.  Ammonium  salts  of  non-volatile  acids. 

Same  method  as  described  §  97,  b,  3,  ft  (potassium  platinic 
chloride).  The  results  obtained  by  these  methods  are  accurate. 

If  you  wish  to  control  the  results,*  ignite  the  double  chloride, 
wrapped  up  in  the  filter,  in  a  covered  crucible,  and  calculate  the 
amount  of  ammonium  from  that  of  the  residuary  platinum.  The 
results  must  agree.  The  heat  must  be  increased  very  gradually.! 

*  If  the  ammonium  platinic  chloride  is  pure,  which  may  be  known  by  its 
color  and  general  appearance,  this  control  may  be  dispensed  with. 

f  The  best  way  is  to  continue  the  application  of  a  moderate  heat  for  a  long 
time,  then  to  remove  the  lid,  place  the  crucible  obliquely,  with  the  lid  leaning 
against  it,  and  burn  the  charred  filter  at  a  gradually-increased  heat  (H.  ROSE). 


§99.]  AMMONIUM.  219 

Want  of  due  caution  in  this  respect  is  apt  to  lead  to  loss,  from 
particles  of  the  double  salt  being  carried  away  with  the  ammonium 
chloride.  Very  small  quantities  of  ammonium  platinic  chloride 
are  collected  on  an  unweighed  filter,  dried,  and  at  once  reduced  to 
platinum  by  ignition.* 

3.   Estimation  by  Expulsion  of  the  Ammonia  in  the  Wet 
Way. 

This  method,  which  is  applicable  in  aU  cases,  may  be  effected 
in  two  different  ways,  viz.  : 

a.  EXPULSION  OF  THE  AMMONIA  BY  DISTILLATION  WITH  SOLUTION 
OF  POTASSA,  or  SODA,  or  with  MILK  OF  LIME. — Applicable  in  all 
cases  where  no  nitrogenous  organic  matters  from  which  ammonia 
might  be  evolved  upon  boiling  with  solution  of  potassa,  &c.,  are 
present  with  the  ammonium  salts. 

Weigh  the  substance  under  examination  in  a  small  glass  tube, 
three  centimetres  long  and  one  wide,  and  put  the  tube,  with  the 
substance  in  it,  into  a  flask  containing  a  suitable  quantity  of  mod- 
erately concentrated  solution  of  potassa  or  soda,  or  milk  of  lime, 
from  which  every  trace  of  ammonia  has  been  removed  by  protracted 
ebullition,  but  which  has  been  allowed  to  get  thoroughly  cold 
again  ;  place  the  flask  in  a  slanting  position  on  wire-gauze,  and 
immediately  connect  it  by  means  of  a  glass  tube  bent  at  an  obtuse 
angle,  with  the  glass  tube  of  a  small  cooling  apparatus.  Connect 
the  lower  end  of  this  tube,  by  means  of  a  tight-fitting  perforated 
cork,  with  a  sufficiently  large  tubulated  receiver  which  is  in  its 
turn  connected  with  a  U-tube  by  means  of  a  bent  tube  passing 
through  its  tubulure. 

If  you  wish  to  determine  voluinetrically  the  quantity  of  ammo- 
IL  in-  expelled,  introduce  the  larger  portion  of  a  measured  quantity 
of  standard  solution  of  acid  (sulphuric,  hydrochloric,  or  oxalic, 
§  192),  into  the  receiver,  the  remainder  into  the  U-tube ;  add  to 
the  portion  of  fluid  in  the  latter  a  little  water,  and  color  the  liquids 
in  the  receiver  and  U-tube  red  with  1  or  2  c.  c.  of  tincture  of  lit- 
mus. The  cooling-tube  must  not  dip  into  the  fluid  in  the  receiver; 
the  fluid  in  the  ll-tube  must  completely  fill  the  lower  part,  but  it 
must  not  rise  high,  as  otherwise  the  passage  of  air  bubbles  might 

*  In  a  series  of  experiments  to  get  the  platinum  from  pure  and  perfectly 
anhydrous  ammonium  platinic  chloride,  by  very  cautious  ignition,  Mr.  Lucius, 
one  of  my  pupils,  obtained  from  44*1  to  44  3  per  cent,  of  the  metal,  instead  of 
44-3. 


220  DETERMINATION.  [§  99. 

easily  occasion  loss  by  spirting.  The  quantity  of  acid  used  must 
of  course  be  more  than  sufficient  to  fix  the  whole  of  the  ammonia 
expelled. 

When  the  apparatus  is  fully  arranged,  and  you  have  ascertained 
that  all  the  joints  are  perfectly  tight,  heat  the  contents  of  the  flask 
to  gentle  ebullition,  and  continue  the  application  of  the  same 
degree  of  heat  until  the  drops,  as  they  fall  into  the  receiver,  have 
for  some  time  altogether  ceased  to  impart  the  least  tint  of  blue  to 
the  portion  of  the  fluid  with  which  they  first  come  in  contact. 
Loosen  the  cork  of  the  flask,  allow  to  stand  half  an  hour,  pour 
the  contents  of  the  receiver  and  U-tube  into  a  beaker,  rinsing  out 
with  small  quantities  of  water,  determine  finally  with  a  standard 
solution  of  alkali  the  quantity  of  acid  still  free,  which,  by  simple 
subtraction,  will  give  the  amount  of  acid  which  has  combined  with 
the  ammonia ;  and  from  this  you  may  now  calculate  the  amount  of 
the  latter  (§  192).  Kesults  accurate.* 

If  you  wish  to  determine  by  the  gravimetric  method  the  quan- 
tity of  ammonia  expelled,  receive  the  ammonia  evolved  in  a  quan- 
tity of  hydrochloric  acid  more  than  sufficient  to  fix  the  whole  of  it, 
and  determine  the  ammonium  chloride  formed,  either  by  simple 
evaporation,  after  the  directions  of  1,  or  as  ammonium  platinic 
chloride,  after  the  directions  of  2. 

b.  EXPULSION  OF  THE  AMMONIA  BY  MILK  OF  LIMP:,  WITHOUT 
APPLICATION  OF  HEAT. — This  method,  recommended  by  SCHLOSING, 
is  based  upon  the  fact  that  an  aqueous  solution  containing  free 
ammonia  gives  off  the  latter  completely,  and  in  a  comparatively 
short  time,  when  exposed  in  a  shallow  vessel  to  the  air,  at  the  com- 
mon temperature.  It  finds  application  in  cases  where  the  presence 
of  organic  nitrogenous  substances,  decomposable  by  boiling  alkalies, 
forbids  the  use  of  the  method  described  in  3,  a  ;  thus,  for  instance, 
in  the  estimation  of  the  ammonia  in  urine,  manures,  &c. 

The  fluid  containing  the  ammonia,  the  volume  of  which  must 
not  exceed  35  c.  c.,  is  introduced  into  a  shallow  flat-bottomed  ves- 
sel from  10  to  12  centimetres  in  diameter;  this  vessel  is  put  on  a 
plate  filled  with  mercury.  A  tripod,  made  of  a  massive  glass  rod, 
is  placed  in  the  vessel  which  contains  the  solution  of  the  ammonium 
salt,  and  a  saucer  or  shallow  dish  with  10  c.  c.  of  the  normal  solu- 
tion of  oxalic  or  sulphuric  acid  (§  192)  put  on  it.  A  beaker  is  now 

*  [In  thus  estimating  minute  quantities  of  ammonia,  the  condensing  tube 
must  be  of  tin,  since  glass  yields  a  sensible  amount  of  alkali  to  hot-water  vapor.] 


§  99.]  AMMONIUM.  221 

inverted  over  the  whole.  The  beaker  is  lifted  up  on  one  side  as 
far  as  is  required,  and  a  sufficient  quantity  of  milk  of  lime  added 
by  means  of  a  pipette  (which  should  not  be  drawn  out  at  the  lower 
end):  The  beaker  is  then  rapidly  pressed  down,  and  weighted 
with  a  stone  slab.  After  forty-eight  hours  the  glass  is  lifted  up, 
and  a  slip  of  moist  reddened  litmus  paper  placed  in  it ;  if  no  change 
of  color  is  observable,  this  is  a  sign  that  the  expulsion  of  the  ammo- 
nia is  complete ;  in  the  contrary  case,  the  glass  must  be  replaced. 
Instead  of  the  beaker  and  plate  with  mercury,  a  bell-jar,  with  a 
ground  and  greased  rim,  placed  air-tight  on  a  level  glass  plate,  may 
be  used.  A  bell-jar,  having  at  the  top  a  tubular  opening,  furnished 
with  a  close-fitting  glass  stopper,  answers  the  purpose  best,  as  it 
permits  the  introduction  of  a  slip  of  red  litmus  paper  suspended 
from  a  thread  ;  thus  enabling  the  operator  to  see  whether  the  com- 
bination of  the  ammonia  with  the  acid  is  completed,  without  the 
necessity  of  removing  the  bell-jar.  According  to  SCHLUSIXG,  forty- 
eight  hours  are  always  sufficient  to  expel  O'l  to  1  gramme  of  ammo- 
nia from  25  to  35  c.  c.  of  solution.  However,  I  caii  admit  this 
statement  only  as  regards  quantities  up  to  0*3  grm. ;  quantities 
above  this  often  require  a  longer  time.  I,  therefore,  always  prefer 
operating  with  quantities  of  substance  containing  no  more  than  0-3 
grm.  ammonia  at  the  most. 

When  all  the  ammonia  has  been  expelled,  and  has  entered  into 
combination  with  the  acid,  the  quantity  of  acid  left  free  is  deter- 
mined bv  means  of  standard  solution  of  alkali,  and  the  amount  of 
the  ammonia  calculated  from  the  result  (§  192). 

4.  Estimation  by  Expulsion  of  the  Nitrogen  in  the  Wet 
Way. 

A  process  for  determining  ammonium  by  means  of  the  azo- 
tometer  has  been  given  by  "W.  KNOP.*  It  depends  on  the  sepa- 
ration of  the  nitrogen  by  a  bromized  and  strongly  alkaline  solution 
of  sodium  hypochlorite.f 

[The  simplest  azotometer  is  that   described   by  RUMPF.^;     It 


*  Chem.  Centralbl.  1860,  244. 

f  This  is  prepared  as  follows: — Dissolve  1  part  of  sodium  carbonate  in  15 
parts  of  water,  cool  the  fluid  with  ice,  saturate  perfectly  with  chlorine,,  keeping 
cold  all  the  while,  and  add  strong  soda  solution  (of  25  per  cent.)  till  the  mixture 
on  rubbing  between  the  fingers  makes  the  skin  slippery.  Before  using,  add  to 
the  quantity  required  for  the  series  of  experiments  bromine  in  the  proportion  of 
2-3  grm.  to  the  litre,  and  shake.  \  Fres.  Zeit.,  VI.  398. 


222 


DETERMINATION. 


consists  of  a  burette  of  50  or  100  c.  c.  stationed  in  a  glass  cylinder 
nearly  filled  with  mercury,  and  connected  by  a  stout  caoutchouc 
tube  with  a  small  bottle,  a,  fig.  49,  to  which  is  fitted  a  soft,  thrice- 
perforated  caoutchouc  stopper.  The  stopper  carries  a  thermometer 
and  two  short  glass  tubes,  one  of  which  joins  it  to  the  burette,  and 
the  other  has  attached  a  short  bit  of  caoutchouc  tubing  and  a  pinch- 
cock,  e.  The  weighed  ammonium  salt  (not  more  than  0'4  grm.)  is 
placed  in  the  tube,  f,  with  10  c«  c.  of  water,  and  50  c.  c.  of  the 
bromized  hypochlorite  solution  are  brought  into  the  bottle,  a. 
The  cock,  e,  being  open,  the  stopper  is  firmly  fixed  in  its  place,  and 
the  burette  is  depressed  in  the  mercury  un- 
til its  uppermost  degree  exactly  coincides 
with  the  surface  of  the  metal.  The  cock  is 
then  closed,  and  the  bottle  is  inclined  to 
bring  the  two  substances  in  contact.  The 
ammonium  salt  is  speedily  decomposed. 
When  no  further  evolution  of  gas  takes 
place  the  burette  is  so  adjusted  that  the 
level  of  the  mercury  without  and  within  it 
shall  nearly  coincide,  and  the  operator  waits 
10-20  minutes,  or  until  the  thermometer  in 
a  indicates  the  same  temperature  as  the  sur- 
rounding air.  Then  the  adjustment  of  the 
burette  to  exact  coincidence  of  the  mercury 
level,  within  and  without,  is  effected,  and 
the  volume  of  the  gas  is  read  off.  The  stand 
of  the  thermometer  and  barometer  are  also 
noted,  and  the  recorded  volume  of  nitrogen 
is  corrected  by  use  of  the  tables  on  pp.  223 
and  224-225,  by  DIETRICH. 

The  first  table  gives  a  correction  for  the 
nitrogen  which  is  absorbed  by  the  60  c.  c.  of  liquid  in  the  bottle  a. 
The  amount  varies  with  the  relative  volumes  of  air  and  nitrogen, 
and  is  determined  empirically  by  decomposing  known  quantities  of 
ammonia  and  noting  the  difference  between  the  obtained  and  the 
theoretical  volume  of  nitrogen.  The  correction  holds  strictly,  of 
course,  only  for  a  solution  of  such  strength  as  that  employed  by 
DIETRICH  and  at  the  mean  temperatures. 

The  second  table  serves  to  spare  the  labor  of  calculation.     The 
weight  of  1  c.  c.  of  nitrogen,  measured  e.  g.  at  T54  mm.  of  barome- 


PJg.  49. 


§99.] 


TABLE   OF  ABSORPTION   OF   NITROGEN   GAS. 


223 


1  I 


«  1 

§    8 

T-l 

s  3 

8    8 

« 

8    8. 

T-<             OJ 

_        1—  1 
Cft        10 

0 

8  5 

g  2 

e  s 

o» 

§       § 

2    9. 

0 

«  1 

%  2 

S    8 

l-H 

«       1 

5    5 

O 

»  1 

B    9 

s  s 

TH 

-  2 

S    9. 

0 

»  1 

s  s? 

iH 

s  2 

«  2 

S    5 

0 

8    1 

s  2 

g    S 

§    ^ 

<M 

*  1 

S    | 

«  2 

g    S 

S    8. 

<M 

a  1 

§    $ 

0 

s  2 

»  s 

§    8 

Oi 

2    8 

0 

s  1 

^9 

g  § 

8    8 

§  ! 

S        « 

o 

T—  1             QQ 

g  s 

T-  1 

•r-l 

?!     °°. 

s  S 

00 

s  § 

-  5 

s  2 

e  S 

-  S 

.    8 

O 

a  5 

5    8. 

1-1 

s  g 

•  1 

CO 
00        °* 

o 

•  i 

9   2 

s  ^ 

T-J 

«    S 

j>    « 

0 

85  5 

*  ii 

s  s 

»  S    : 

00 

cc      *-; 
o 

«  1 

»  s 

^        . 

1—  1 

«  5 

«  2    : 

<D 
O        '" 
0 

a  1 

«  2 

8    S 

-  2  ; 

CO 

^     ^ 
o 

*  1 

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S    8 

T—  1 

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CO        T-" 

0 

«  1 

9    S 

rH 

8    § 

«  2 

«    8 

0 

«  1 

9  S 

§  3 

•  1    1 

~  s 

0 

«    1 

-  s 

s  s 

s  i    i 

Evolved  
Absorbed  

Evolved  
Absorbed  

Evolved.  ,  
Absorbed  

Evolved  
Absorbed  

tj 

rt3             « 

1      1 

O        tn 
>       ^ 
W       <             i 

224 


TABLE   OF   WEIGHTS. 


[§99. 


II.  TABLE   OF  THE  WEIGHT  OF  A 

In  Milligrammes  for  Pressures  from  720  to  770  mm/ 

MILLIMETRES. 


720 


722 


724 


726 


728  i  730  732  I  734  I  736  I  738  !  740  742 


744 


10*  1.18880  1,18699  1.14018  1.14337  1.146561.14975  1.15294  1.15613  1.16988 1.16261  1.16570  1.16889  1.17208 

i          i     i         ;     -     j     i     i 

11»  1.13881 1 1.18199  1.13517,1.13835  1.14153  1.144711. 14789;!. 15107  1.154241.15742  1.16060  1.16378  1.16696 

i  ; 

12°  1.12376  1.12693  1.13010J1.13326  1.13643'l.l3960  1.14277  1.14593!1.14910^1. 152271. 15543  1.15860  1.16177 

I      ! 

1.11875  1.12191  1.12506:1.12822  1.13138;  1.13454  1.13769  1.14085  1.1440l|l.l4716  1.15032  1.15348  1.15663 


14°  1.1186911.11684  1.1199911.1231311.12628  1. 12942 !  1.13257  1.13572 '  1.18886  1.14201 


1.14515  1.14830  1.15145 


1.10346  1.10658'1.10971'1.11283!1.115961.11908  1.12220  1.12533  1.12845'l.l3158il. 13470  1.13782J1.14095 


15°  1.10859(1.11172  1.11486!!.  11799  1.12113  1.12426  1.12739  1.13053  1.13366' 1.13680  1.13993  1.14306!  1.14620 

I  I 


17° 


1.09828  1.10139  1.10450  1.10761 1.11078 1.li884  1.11695  1.12006  1.12317:1.12629  1.12940  1.13251;  1.13562 


18°  1.09304  1.09614  1.09924il. 10234  1.10544  1.10854  1.11165  1.11475  1.11785  1.120951.12405  1.12715  1.13025 

i  r-  Vt       -         -f  I 

19°  1.08744  1.09083  1.09392:1.09702  1.10011  1.10320  1.106291.10938  1.11248  1.11557  1.118661.12175  1.12484 

|  i  |  i  j  I  l  |  i  | 

20°|l.08246il.08554  1.08862|l.09170  1.094781.09786|1.100941. 10402  1.107101.11018  1.11327  1.11635  1.11943 

i          i          :          i 

21°  1.077081.080151.08322  1. 08629k 08936  J. 09243;  1.09550  1.09857  1.10165|1. 10472  1.107791. 11086!1. 11393 


22°  1.071661. 074721.07778!l.080841.083901.08696  1.090021.09308  1.096141.09921  1.10227  1.10533  1.10839 

r.  i  II 

23°  1.06616, 1.06921  1.07226  1.07531  1.078361.08141 

! 

21°. 1.06061  1.063651.06669  1.06973  1.07277  1.07581 

i  | 


1.05499  1.058011.06104  1.06407 '1.06710  1.07013  1.073161.07619  1.07922  1.08225  1.08528  1.08831 


1.08446  1.08751  1.09056  1.09361  1.09666  1.09971 


1.078851.081891.084931 1.08796  1.091001.09404 


1.10276 


1.09708 


1.09134 


720 


722  !  724 


726 


728 


730 


732 


734 


736 


738 


740 


742 


744 


MILLIMETRES. 


§99.] 


TABLE   OF    WEIGHTS. 


225 


CUBIC   CENTIMETRE  OF  NITROGEN. 

of  Mercury,  and  for  Temperatures  from  10°  to  25°  C. 

MILLIMETRES. 


746 

748  |  750      752 

754 

756 

758 

760     762 

764 

766 

768 

770 

; 

i 

1.17527  1.17846'  1.18165 

1.18484 

1.18803 

1.19122 

1.  19441  jl.  19760  1.20079  1.20398  1.20717  1.21036 

1.21355;  io°i 

1.17014:1.17332  1.17650 

1.17168 

1.18286 

1.18603 

1.18921J1.192394.19557  1.19875 

1.201931.20511 

1.20829;  11- 

1.16493  1.16810  1.17127  1.  174444.  17760  1.18077  1.18394  1.18710  1.19027  1.19344 

1.196601.19977 

1.20294J  12° 

1.15979 

1.16295  1.16611  1.16926  1.17242  1.17558  1.17873  1.18189 

1.18505  1.18820 

1.191361.19452 

1.19768    13<> 

1.15459 

1.15774  1.16088  1.16403  1.16718 

1.17032J1.17347 

1.17661 

1.17976  118291 

1.186051.18920 

1.19234    14° 

1.14933 

1.15247  1.15560  1.15873 

1.16187 

1.16500 

1.16814 

1.17127 

1.17440  1.17754 

1.18067 

1.18381 

1.18694    15° 

1.144071.147201.150321.15344 

1.15657 

1.15969 

1.16282 

1.16594 

1.16906  1.17219 

1.17531 

1.17844 

1.  18156  |  16° 

1.13873  '1.14185  1.14496  1.14807 

1.15118 

1.15429 

1.15741 

1.16052 

1.163631.16674 

1.16985 

1.17297 

1.1700S    17- 

1.13335  1.13645  1.13955  1.14266 

1.14576 

1.148861.15196  1.15506 

; 

1.15816  1.16126  1.16436 

1.16746 

1.17056,  18° 

1.12794  1.13103  1.13412 

1.13721 

1.14340  1.14649  1.14958  1.15267  1.15576  1.15886  1.16195 

1.16504    19° 

1.12251  1.12559 

1.12867 

1.13175  1.13483 

1.13791 

1.14099 

1.14406;!.  14716 

1.15024 

1.15332  1.15640 

1.15948;  20° 

1.11700  1.12007 

1.12314 

1.12621 

1.12928 

1.13236  1.13543  1.13850  1.14157 

1.14464 

1.14771  1.15078 

1.15385J  21°; 

1 

1.11145 

1.11451 

1.11757 

1.12063 

1.12369 

1.12675 

1.12982 

1.13288  1.13594:1.13900  1.14206  1.14512 

1.14818|  22° 

1.10581 

1.10886 

1.11191 

1.11496 

1.11801 

1.12106 

1,12411 

1.12716 

1.13021  1.133261.13631  1.13936 

1.14241)  23° 

| 

1.10012 

1.10316 

1.10620  1.10924  1.11228 

1.11532J1.11835  1.12139 

1.12443,1.12747:1.13051  .1.13355 

1.13659    24° 

1.09437 

1.09740 

1.10043 

1.10346 

1.10649 

1.10952  1.11255  1.11558  1.11861 

1.12164 

1.12467 

1.12770 

1.13073J  25° 

] 

746 

748 

750 

752 

754 

756 

758 

760 

762 

764 

766 

768     770 

MILLIMETRES. 


226  DETERMINATION.  [§  100. 

ter  and  15°  C.,  is  found  at  the  intersection  of  the  vertical  column 
754  with  the  horizontal  column  15°,  is,  viz.,  1-16187.   • 

To  the  observed  volume  of  nitrogen  add  the  amount  absorbed 
as  per  Table  L,  and  correct  the  total  by  Table  II.  It  scarcely 
requires  to  be  mentioned  that  good  results  can  only  be  obtained  in 
an  apartment  where  the  temperature  is  uniform,  and  when  care  is 
exercised  to  avoid  warming  the  apparatus  in  handling.  See  DIET- 
KICH'S  papers.* 

§  100. 

Supplement  to  the  First  Group. 
LITHIUM. 

In  the  absence  of  other  bases,  lithium  may,  like  potassium 
and  sodium,  be  converted  into  anhydrous  SULPHATE,  and  weighed 
in  that  form  (Li2SO4).  As  lithium  forms  no  acid  sulphate,  the 
excess  of  sulphuric  acid  may  be  readily  removed  by  simple  igni- 
tion. LITHIUM  CARBONATE  also,  which  is  difficultly  soluble  in 
water,  and  fuses  at  a- red  heat  without  suffering  decomposition,  is 
well  suited  for  weighing  ;  whilst  lithium  chloride,  which  deliquesces 
in  the  air,  and  is  by  ignition  in  moist  air  converted  into  hydro- 
chloric acid  and  lithium  oxide,  is  unfit  for  the  estimation  of 
lithium. 

In  presence  of  other  alkali  metals,  lithium  is  best  converted 
into  LITHIUM  PHOSPHATE  (Li3PO4),  and  weighed  in  that  form.  This  is 
effected  by  the  following  process:  add  to  the  solution  a  sufficient 
quantity  of  sodium  phosphate  (which  must  be  perfectly  free  from 
phosphates  of  the  alkali-earth  metals),  and  enough  soda*  to  keep  the 
reaction  alkaline,  and  evaporate  the  mixture  to  dry  ness ;  pour 
water  over  the  residue,  in  sufficient  quantity  to  dissolve  the  soluble 
salts  with  the  aid  of  a  gentle  heat,  add  an  equal  volume  of  solution 
of  ammonia,  "digest  at  a  gentle  heat,  filter  after  twelve  hours,  and 
wash  the  precipitate  with  a  mixture  of  equal  volumes  of  water  and 
solution  of  ammonia.  Evaporate  the  filtrate  and  first  washings  to 
dryness,  and  treat  the  residue  in  the  same  way  as  before.  If  some 
more  lithium  phosphate  is  thereby  obtained,  add  this  to  the  prin- 
cipal quantity.  The  process  gives,  on  an  average,  99*61  for  100 
parts  of  lithium  oxide. 


*  Fres.  Zeit.  III.  162;  IV.  141,  and  V.  36. 


§  101.]  BARIUM.  227 

If  the  quantity  of  lithium  present  is  relatively  very  small, 
the  larger  portion  of  the  potassa  or  soda  compounds  should  first  be 
removed  by  addition  of  absolute  alcohol  to  the  most  highly  con- 
centrated solution  of  the  salts  (chlorides,  bromides,  iodides,  or 
nitrates,  but  not  sulphates) ;  since  this,  by  lessening  the  amount  of 
water  required  to  effect  the  separation  of  the  lithium  phosphate 
from  the  soluble  salts,  will  prevent  loss  of  lithium  (W.  MAYER).* 

The  precipitated  normal  lithium  phosphate  has  the  formula 
2Li3PO4  +  H3O.  It  dissolves  in  2539  parts  of  pure,  and 
3920  parts  of  ammoniated  water ;  at  100°,  it  completely  loses  its 
water ;  if  pure,  it  does  not  cake  at  a  moderate  red  heat  (MAYER). 

The  objections  raised  by  KAMMELSBERof  to  MAYER'S  method 
of  estimating  lithia  I  find  to  be  ungrounded.  According  to  my 
own  experience,  it  appears  that  the  filtrate  and  wash- water  must 
be  evaporated  in  a  platinum  dish  not  only  once,  but  at  least  twice 
—in  fact,  till  a  residue  is  obtained  which  is  completely  soluble  in 
dilute  ammonia.  Lithium  phosphate  may  be  dried  at  100°,  or 
ignited  according  to  §  53,  before  being  weighed.  In  the  latter 
case,  care  must  be  taken  to  free  the  filter  as  much  as  possible  from 
the  precipitate  before  proceeding  to  incinerate  it.  I  have  thus 
obtained,  J  instead  of  100  parts  lithium  carbonate,  by  drying  at 
100°,  99-84,  99-89,  100-41,— by  "igniting  99*66  and  100-05.  The 
lithium  phosphate  obtained  was  free  from  sodium. 

Second  Group. 

BARIUM STRONTIUM CALCIUM MAGNESIUM. 

§  101. 

1.  BARIUM. 

a.  Solution. 

Caustic  baryta  is  soluble  in  water,  as  are  many  barium  salts. 
Barium  salts  which  are  insoluble  in  water  are,  with  almost  the 
single  exception  of  the  sulphate,  readily  dissolved  by  dilute  hydro- 
chloric acid.  The  solution  of  the  sulphate  is  effected  by  fusion 
with  sodium  carbonate,  &c.  (See  §  132.) 

*  Annal.  der  Chem.  u.  Pharm.  98,  193,  where  Mayer  has  also  demonstrated 
the  non-existence  of  a  sodium  lithium  phosphate  of  fixed  composition  (Berzelius), 
or  of  varying  composition  (Rammelsberg). 

f  Pogg.  Annal.  102,  443.  \  Zeitschr.  f.  Analyt.  Chem.  1,  42. 


228  DETERMINATION.  [§  101. 

b.  Determination. 

Barium  is  weighed  either  as  sulphate  or  as  carbonate,  rarely 
(in  the  separation  from  strontia)  as  barium  silico-fluoride  (§  71). 
Barium  oxide  or  hydroxide,  also  barium  carbonate,  may  also  be 
determined  by  the  volumetric  (alkalimetric)  method.  Comp. 
§198. 

We  may  convert  into 

1.  BARIUM  SULPHATE. 

a.  By  Precipitation.  b.  By  Evaporation*. 

All  barium  compounds  with-  All  barium  salts  of  volatile 

out  exception.  acids,  if   no  other   non-volatile 

body  is  present. 

2.  BAKIUM  CARBONATE. 

a.  All  barium  salts  soluble  in  water. 

b.  Barium  salts  of  organic  acids. 

Barium  is  both  precipitated  and  weighed,  by  far  the  most  fre- 
quently as  sulphate,  the  more  so  as  this  is  the  form  in  which  it  is 
most  conveniently  separated  from  other  bases.  The  determination 
by  means  of  evaporation  (1,  b)  is,  in  cases  where  it  can  be  applied, 
and  where  we  are  not  obliged  to  evaporate  large  quantities  of  fluid, 
very  exact  and  convenient.  Barium  is  determined  as  carbonate  in 
the  wet  way,  when  from  any  reason  it  is  not  possible  or  not  desir- 
able to  precipitate  it  as  sulphate.  If  a  fluid  or  dry  substance  con- 
tains bodies  which  impede  the  precipitation  of  barium  as  sulphate 
or  carbonate  (alkali  citrates,  metaphosphoric  acid,  see  §  71,  a  and 
b\  such  bodies  must  of  course  be  got  rid  of,  before  proceeding  to 
precipitation. 

1.  Determination  as  Barium,  Sulphate. 

a.  By  Precipitation. 

Heat  the  moderately  dilute  solution  of  barium,  which  must  not 
contain  too  much  free  acid  (and  must,  therefore,  if  necessary,  first 
be  freed  therefrom  by  evaporation  or  addition  of  sodium  carbo- 
nate), in  a  platinum  or  porcelain  dish,  or  in  a  glass  vessel,  to  incipi- 
ent ebullition,  add  dilute  sulphuric  acid,  as  long  as  a  precipitate 
forms,  keep  the  mixture  for  some  time  at  a  temperature  very  near 
the  boiling  point,  stirring  if  not  on  a  water-bath,  and  allow  the 
precipitate  to  subside  ;  decant  the  almost  clear  supernatant  fluid  on 
a  filter,  boil  the  precipitate  once  with  water  and  a  little  dilute  sul- 


§  101.]  BARIUM.  229 

phuric  acid,  then  three  or  four  times  with  water,  then  transfer  it 
to  the  filter,  and  wash  with  boiling  water,  until  the  filtrate  is  no 
longer  rendered  turbid  by  barium  chloride.  Dry  the  precipitate, 
and  treat  it  as  directed  in  §  53.  If  the  precipitate  has  been 
properly  washed  in  the  manner  here  directed,  it  is  perfectly  pure. 
In  the  presence  of  alkali  salts,  however,  the  precipitate  will  still 
contain  small  quantities  of  alkali  sulphate. 

b.  By  Evaporation. 

Add  to  the  solution,  in  a  weighed  platinum  dish,  pure  sulphuric 
acid  very  slightly  in  excess,  and  evaporate  on  the  water-bath; 
expel  the  excess  of  sulphuric  acid  by  cautious  application  of  heat, 
and  ignite  the  residue. 

For  the  properties  of  barium  sulphate,  see  §  71. 

Both  methods,  if  properly  and  carefully  executed,  give  almost 
absolutely  accurate  results. 

2.  Determination  as  Barium  Carbonate. 

a.  In  Solutions. 

Mix  the  moderately  dilute  solution  of  the  barium  salt  in  a 
beaker  with  ammonia,  add  ammonium  carbonate  in  slight  excess, 
and  let  the  mixture  stand  several  hours  in  a  warm  place.  Filter, 
wash  the  precipitate  with  water  mixed  with  a  little  ammonia,  dry, 
fljid  ignite  (§  53). 

For  the  properties  of  the  precipitate,  see  §  71.  This  method 
involves  a  trifling  loss  of  substance,  as  barium  carbonate  is  not 
absolutely  insoluble  in  water.  The  direct  experiment,  No.  62, 
gave  99-79  instead  of  100. 

If  the  solution  contains  a  notable  quantity  of  ammonium  salts, 
the  loss  incurred  is  much  more  considerable,  since  the  presence  of 
such  salts  greatly  increases  the  solubility  of  barium  carbonate. 

b.  In  Barium  Salts  of  Organic  Acids. 

Heat  the  salt  slowly  in  a  covered  platinum  crucible,  until'  no 
more  fumes  are  evolved;  place  the  crucible  obliquely,  with  the 
lid  leaning  against  it,  and  ignite,  until  the  whole  of  the  carbon  is 
consumed,  and  the  residue  presents  a  perfectly  white  appear- 
ance :  moisten  the  residue  with  a  concentrated  solution  of  ammo- 
nium carbonate,  evaporate,  ignite  gently,  and  weigh.  The  results 
obtained  by  this  method  are  quite  satisfactory.  A  direct  experi- 
ment, No.  63,  gave  99'61  instead  of  100.  The  loss  of  substance 
which  almost  invariably  attends  this  method  is  owing  to  particles 


230  DETERMINATION.  [§  102. 

of  the  salt  being  carried  away  with  the  fumes  evolved  upon  igni- 
tion, and  is  accordingly  the  less  considerable,  the  more  slowly  and 
gradually  the  heat  is  increased.  Omission  of  the  moistening  of 
the  residue  with  ammonium  carbonate  would  involve  a  further  loss 
of  substance,  as  the  ignition  of  barium  carbonate  in  contact  with 
carbon  is  attended  with  formation  of  some  caustic  baryta,  carbon 
monoxide  gas  being  evolved. 

§102. 

2.  STRONTIUM. 

a.  Solution. 

See  the  preceding  paragraph  (§  101,  a. — Solution  of  baryta  and 
barium  salts),  the  directions  there  given  apply  equally  here. 

b.  Determination. 

Strontium  is  weighed  either  as  strontium  sulphate  or  as  stron- 
tium carbonate  (§  72).  Strontium  in  the  form  of  oxide,  hydrox- 
ide, or  carbonate,  may  be  determined  also  by  the  volumetric 
(alkalimetric)  method.  Comp.  §  198. 

We  may  convert  into 

1.  STRONTIUM  SULPHATE. 
a.  J3y  Precipitation. 

All  compounds  of  strontium  without  exception. 
ft.  By' Evaporation. 

All  strontium  salts  of  volatile  acids,  if  110  other  non-volatile 
body  is  present. 

2.  STRONTIUM  CARBONATE. 

a.  All  strontium  compounds  soluble  in  water. 

/3.  Strontium  salts  of  organic  acids. 

The  method  based  on  the  precipitation  of  strontium  with  sul- 
phuric acid  yields  accurate  results  only  in  cases  where  the  fluid 
from  which  the  strontium  is  to  be  precipitated  may  be  mixed, 
without  injury,  with  alcohol.  Where  this  cannot  be  done,  and 
where  the  method  based  on  the  evaporation  of  the  solution  of 
strontium  with  sulphuric  acid  is  equally  inapplicable,  the  conver- 
sion into  the  carbonate  ought  to  be  resorted  to  in  preference,  if 
admissible.  As  in  the  case  of  barium,  so  here,  we  have  to  be  on 
our  guard  against  the  presence  of  substances  which  would  impede 
precipitation. 


§  102.]  STRONTIUM.  231 

1.  Determination  as  Strontium  Sulphate. 

a.  By  Precipitation. 

Mix  the  solution  of  the  strontium  salt  (which  must  not  be  too 
dilute,  nor  contain  much  free  hydrochloric  or  nitric  acid)  with 
dilute  sulphuric  acid  in  excess,  in  a  beaker,  and  add  at  least  an 
equal  volume  of  alcohol;  let  the  mixture  stand  twelve  hours, 
and  filter ;  wash  the  precipitate  with  dilute  alcohol,  dry  and  ignite 
(§  53). 

If  the  circumstances  of  the  case  prevent  the  use  of  alcohol,  the 
fluid  must  be  precipitated  in  a  tolerably  concentrated  state,  allowed 
to  stand  in  the  cold  for  at  least  twenty-four  hours,  filtered,  and  the 
precipitate  washed  with  cold  water,  until  the  last  rinsings  manifest 
no  longer  an  acid  reaction,  and  leave  no  perceptible  residue  upon 
evaporation.  If  traces  of  free  sulphuric  acid  remain  adhering  to 
the  filter,  the  latter  turns  black  on  drying,  and  crumbles  to  pieces ; 
too  protracted  washing  of  the  precipitate,  on  the  other  hand,  tends 
to  increase  the  loss  of  substance. 

Care  must  be  taken  that  the  precipitate  be  thoroughly  dry, 
before  proceeding  to  ignite  it ;  otherwise  it  will  be  apt  to  throw 
off  fine  particles  during  the  latter  process.  The  filter,  which  is  to 
be  burnt  apart  from  the  precipitate,  must  be  as  clean  as  possible, 
or  some  loss  of  substance  will  be  incurred ;  as  may  be  clearly  seen 
from  the  depth  of  the  carmine  tint  of  the  flame  with  which  the 
filter  burns  if  the  precipitate  has  not  been  properly  removed. 

For  the  properties  of  the  precipitate,  see  §  72.  When  alcohol 
is  used  and  the  directions  given  are  properly  adhered  to,  the  results 
are  very  accurate ;  when  the  sulphate  of  strontium  is  precipitated 
from  an  aqueous  solution,  on  the  contrary,  a  certain  amount  of  loss 
is  unavoidable,  as  strontium  sulphate  is  not  absolutely  insoluble  in 
water.  The  direct  experiments,  No.  64,  gave  only  98'12  and  98*02 
instead  of  100.  However,  the  error  may  be  rectified,  by  calculat- 
ing the  amount  of  strontium  sulphate  dissolved  in  the  filtrate  and 
the  wash-water,  basing  the  calculation  upon  the  known  degree  of 
solubility  of  strontium  sulphate  in  pure  and  acidified  water.  See 
Expt.  No.  65,  which,  with  this  correction,  gave  99'77  instead  of 
100.  The  necessity  for  making  the  correction  may  be  obviated  by 
washing  with  1  part  sulphuric  acid  mixed  with  20  parts  water  till 
all  substances  precipitable  by  alcohol  are  removed,  then  with  alco- 
hol till  all  the  sulphuric  acid  is  removed.  Strontium  sulphate  also 
carries  down  sulphates  of  other  strong  bases  in  small  quantities. 


232  DETERMINATION.  [§  103. 

b.  By  Evaporation. 

The  same  method  as  described  for  barium,  §  101,  1,  b. 

2.  Determination  as  Strontium  Carbonate. 

a.  In  Solutions. 

The  same  method  as  described  §  101,  2,  a.  For  the  proper- 
ties of  the  precipitate,  see  §  72.  The  method  gives  very  accurate 
results,  as  strontium  carbonate  is  nearly  absolutely  insoluble  in 
water  containing  ammonia  and  ammonium  carbonate.  A  direct 
experiment,  No.  66,  gave  99*82  instead  of  100.  Presence  of 
ammonium  salts  exercises  here  a  less  adverse  influence  than  the 
precipitation  of  barium  carbonate. 

b.  In  Salts  of  Organic  Acids. 

The  same  method  as  described  §  101,  2,  b.  The  remarks  made 
there,  respecting  the  accuracy  of  the  results,  apply  equally  here. 

§103. 

3.  CALCIUM. 

a.  Solution. 

See  §  101,  a. — Solution  of  barium.  Calcium  fluoride  is,  by 
means  of  sulphuric  acid,  converted  into  calcium  sulphate,  and  the 
latter  again,  if  necessary,  decomposed  by  boiling  or  fusing  with 
an  alkali  carbonate  (§132).  [Calcium  sulphate  dissolves  readily 
in  moderately  dilute  hydrochloric  acid.  It  is  much  less  soluble  in 
strong  hydrochloric  acid.] 

b.  Determination. 

Calcium  is  weighed  either  as  calcium  sulphate,  as  calcium 
carbonate,  or  calcium  oxide  (§  73).  Calcium  in  the  form  of  oxide, 
hydroxide,  or  carbonate,  may  be  determined  also  by  the  volumetric 
(alkalimetric)  method.  Comp.  §  198.' 

We  may  convert  into 

1.  CALCIUM  SULPHATE. 

a.  By  Precipitation. 

All  calcium  salts  of  acids  soluble  in  alcohol,  provided  no  other 
substance  insoluble  in  alcohol  be  present. 

b.  By  Evaporation. 

All  calcium  salts  of  volatile  acids,  provided  no  non- volatile  body 
be  present. 


§  103.]  (  ALCIUM.  233 

2.  CALCIUM  CARBONATE. 

a.  By  Precipitation  with  Ammon          Carbonate. 
All  calcium  salts  soluble  in  water. 

b.  By  Precipitation  with  A  nun  oitium,  Oxalate. 

All  calcium  salts  soluble  in  water  or  in  hydrochloric  acid  with- 
out exception. 

c.  By  Ignition. 

( 'alcium  salts  of  organic  acids. 

Of  these  several  methods,  2,  b  (precipitation  with  ammonium 
oxalate)  is  the  one  most  frequently  resorted  to.  This,  and  the 
method  1,  J,  give  the  most  accurate  results.  The  method,  1,  a,  is 
usually  resorted  to  only  to  effect  the  separation  of  calcium  from 
other  basic  radicals ;  2,  #,  generally  only  to  effect  the  separation 
of  calcium  together  with  the  other  alkali-earth  metals  from  the 
alkalies.  As  many  bodies  (alkali  citrates,  and  metaphosphates) 
interfere  with  the  precipitation  of  calcium  by  the  precipitants 
given,  these,  if  present,  must  be  first  removed. 

1.  Determination  of  Calcium  Sulphate. 

a.  By  Precipitation. 

Mix  the  solution  of  calcium  salt  in  a  beaker,  with  dilute  sul- 
phuric acid  in  excess,  and  add  twice  the  volume  of  alcohol ;  let 
the  mixture  stand  twelve  hours,  filter,  and  thoroughly  wash  the 
precipitate  with  alcohol,  dry.  and  ignite  moderately  (§  53).  For 
the  properties  of  the  precipitate,  see  §  73.  The  results  are  very 
accurate.  A  direct  experiment,  No.  67,  gave  99'64  instead  of  100. 

b.  By  Evaporation. 

The  same  method  as  described  §  101,  1,  b. 

2.  Determination   as    Calcium    Carbonate   or    Calcium 
Oxide. 

a.  By  Precipitation  with  Ammonium  Carbonate. 

The  same  method  as  described  §  101,  2,  a.  The  precipitate 
can  be  most  conveniently  weighed  as  calcium  carbonate.  It  must 
be  exposed  only  to  a  very  gentle  red  heat,  but  this  must  be  con- 
tinued for  some  time.  For  the  properties  of  the  precipitate,  see 
§73. 

This  method  gives  very  accurate  results,  the  loss  of  substance 
incurred  being  hardly  worth  mentioning. 

If  the  solution  contains  ammonium  chloride  or  similar  ammo- 


234  DETERMINATION.  [§  103. 

niurn  salts  in  considerable  proportion,  the  loss  of  substance  incurred 
is  far  greater.  The  same  is  the  case  if  the  precipitate  is  washed 
with  pure  instead  of  ammoniacal  water.  A  direct  experiment,  No. 
68,  in  which  pure  water  was  used,  gave  99*17  instead  of  100  parts 
of  lime. 

J.  J3y  Precipitation  with  A.?nnionium  Oxalate. 
a.   The  Calcium  Salt  is  soluble  in  Water. 

To  the  hot  solution  in  a  beaker,  add  ammonium  oxalate  in 
moderate  excess,  and  then  ammonia  sufficient  to  impart  an  ammo- 
niacal smell  to  the  fluid;  cover  the  glass,  and  let  it  stand  in  a 
warm  place  until  the  precipitate  has  completely  subsided,  which 
will  require  twelve  hours,  at  least.  Pour  the  clear  fluid  gently  and 
cautiously,  so  as  to  leave  the  precipitate  undisturbed,  on  a  filter ; 
wash  the  precipitate  two  or  three  times  by  decantation  with  hot 
water ;  lastly,  transfer  the  precipitate  also  to  the  filter,  by  rinsing 
with  hot  water,  taking  care,  before  the  addition  of  a  fresh  portion, 
to  wait  until  the  fluid  has  completely  passed  through  the  filter. 
Small  particles  of  the  precipitate,  adhering  firmly  to  the  glass, 
are  removed  with  a  feather.  If  this  fails  to  effect  their  complete 
removal,  they  should  be  dissolved  in  a  few  drops  of  highly  dilute 
hydrochloric  acid,  ammonia  added  to  the  solution,  and  the  oxalate 
obtained  added  to  the  first  precipitate.  Deviations  from  the  rules 
laid  down  here  will  generally  give  rise  to  the  passing  of  a  turbid 
fluid  through  the  filter.  After  having  washed  the  precipitate,  dry 
it  on  the  filter  in  the  funnel,  and  transfer  the  dry  precipitate  to  a 
platinum  crucible,  taking  care  to  remove  it  as  completely  as 
possible  from  the  filter;  burn  the  filter  on  a  piece  of  platinum 
wire,  letting  the  ash  drop  into  the  hollow  of  the  lid ;  put  the 
latter,  now  inverted,  on  the  crucible,  so  that  the  filter  ash  may  not 
mix  with  the  precipitate ;  heat  at  first  very  gently,  then  more 
strongly,  until  the  bottom  of  the  crucible  is  heated  to  very  faint 
redness.  Keep  it  at  that  temperature  from  ten  to  fifteen  minutes, 
removing  the  lid  from  time  to  time.  I  am  accustomed  during  this 
operation  to  move  the  lamp  backwards  and  forwards  under  the 
crucible  with  the  hand,  since,  if  you  allow  it  to  stand,  the  heat 
may  very  easily  get  too  high.  Finally  allow  to  cool  in  the  desic- 
cator and  weigh.  After  weighing,  moisten  the  contents  of  the 
crucible,  which  must  be  perfectly  white,  or  barely  show  the  least 
tinge  of  gray,  with  a  little  water,  and  test  this  after  a  time  with  a 


£  103.]  CALCIUM.  235 

minute  slip  of  turmeric  paper.  Should  the  paper  turn  brown — a 
sign  that  the  heat  applied  was  too  strong — rinse  off  the  fluid 
adhering  to  the  paper  with  a  little  water  into  the  crucible,  throw 
in  a  small  lump  of  pure  ammonium  carbonate,  evaporate  to  dry- 
ness  (best  in  the  water-bath),  heat  to  very  faint  redness,  and  weigh 
the  residue.  If  the  weight  has  increased,  repeat  the  same  opera- 
tion until  the  weight  remains  constant.  This  method  gives  nearly 
absolutely  accurate  results;  and  if  the  application  of  heat  is 
properly  managed,  there  is  no  need  of  the  tedious  evaporation 
with  ammonium  carbonate.  A  direct  experiment,  No.  69,  gave 
99-99  instead  of  100. 

If  a  gas  blowpipe  is  at  hand,  or  any  other  arrangement  by 
means  of  which  a  platinum  crucible  may  be  raised  to  a  white  heat, 
the  calcium  oxalate  may  be  converted  into  CAUSTIC  LIME  with 
results  almost  equally  accurate;  and  I  believe  that  this  method, 
which  requires  less  patience  than  the  other,  is  more  certain  to  yield 
good  results  in  the  hands  of  many  persons.  The  calcium  oxalate 
and  the  filte^  ash  are  transferred  to  a  moderate-sized  platinum 
crucible,  which  is  ignited  first  over  the  BI.NSKX.  and  then  over  the 
blowpipe.  The  crucible  is  then  weighed,  and  ignited  again  over 
the  blowpipe.  The  second  ignition  over  the  blowpipe  should  not 
reduce  the  weight.  The  duration  of  the  ignition  necessary  varies 
from  5  to  15  or  more  minutes,  according  to  intensity  of  heat  and 
quantity  of  the  precipitate.  It  is  well  to  weigh  the  empty  crucible 
again  at  the  end  of  the  operation,  as  platinum  sometimes  loses 
weight  after  violent  and  prolonged  ignition.  The  results  obtained 
by  FRITZSCHE,  COSSA,*  and  SOUCHAY  scarcely  differ  from  the  calcu- 
lated numbers.  For  properties  of  calcium  oxide,  see  §  73. 

The  calcium  oxalate  may  also  be  converted  into  SULPHATE. 
SCHROTTER  ignites  in  a  covered  platinum  crucible  with  pure  ammo- 
nium sulphate.  Or  you  may  ignite  in  a  covered  platinum  dish 
till  the  precipitate  is  for  the  most  part  converted  into  oxide,  add  a 
little  water,  then  hydrochloric  acid  to  effect  solution,  then  pure 
.sulphuric  acid  in  excess,  evaporate  and  ignite  moderately.  This 
process  is  also  quite  accurate. 

Instead  of  converting  calcium  oxalate  into  carbonate  or  oxide 
for  weighing,  the  quantity  of  calcium  present  in  the  salt  may  be 
determined  also  by  two  different  volumetric  methods. 


*  FRITZSCHE  (Zeitschr.  f.  anal.  Chem.  3,  179)  and  A.  COSSA  (Ib.  8,  141). 


236  DETERMINATION.  [§ 

a.  Ignite  the  oxalateT  converting  it  thus  into  a  mixture  of  cal- 
cium carbonate  and  oxide,  and  determine  the  quantity  of  the  cal- 
cium by  the  alkalimetric  method  described  in  §  198  ;  or, 

b.  Determine  the  oxalic  acid  in  the  well-washed  but  still  moist 
calcium  oxalate  by  means  of  potassium  permanganate  (§  137). 

With  proper  care,  both  these  volumetric  methods  give  as  accu- 
rate results  as  those  obtained  by  weighing.  (Comp.  Expt.  No. 
71.)  They  deserve  to  be  recommended  more  particularly  in  cases- 
where  an  entire  series  of  quantitative  estimations  of  calcium  has 
to  be  made.  Under  certain  circumstances  it  may  also  prove 
advantageous  to  precipitate  calcium  with  a  measured  quantity  of  a 
standard  solution  of  oxalic  acid,  filter,  and  determine  the  excess  of 
oxalic  acid  in  the  filtrate,  or  an  aliquot  part  of  the  same.  (KRAUT.*) 
/?.  The  Salt  is  insoluble  in  Water. 

Dissolve  the  salt  in  dilute  hydrochloric  acid.  If  the  acid  of 
the  calcium  salt  is  of  a  nature  to  escape  in  this  operation  (e.g.,  cai 
bonic  acid),  or  to  admit  of  its  separation  by  evaporation  (e.g.,  silicic 
acid),  proceed,  after  the  removal  of  the  acid,  as  directed  in  a.  But 
if  the  acid  cannot  thus  be  readily  got  rid  of  (e.g.,  phosphoric  acid), 
proceed  as  follows :  Add  ammonia  until  a  precipitate  begins  to 
form,  re-dissolve  this  with  a  drop  of  hydrochloric  acid,  add  ammo- 
nium oxalate  in  excess,  and  finally  sodium  acetate;  allow  the 
precipitate  to  subside,  and  proceed  for  the  remainder  of  the  opera- 
tion as  directed  in  a.  In  this  process  the  free  hydrochloric  acid 
present  reacts  on  the  sodium  acetate  and  ammonium  oxalate, 
forming  sodium  and  ammonium  chlorides,  with  liberation  of  a 
corresponding  amount  of  oxalic  and  acetic  acids  in  which  calcium 
oxalate  is  nearly  insoluble.  The  method  yields  accurate  results. 
A  direct  experiment,  No.  72,  gave  99'78  instead  of  100. 

c.  By  Ignition. 

The  same  method  as  described  §  101,  2,  b  (barium).  The  resi- 
due remaining  upon  evaporation  with  ammonium  carbonate  (which 
operation  it  is  advisable  to  perform  twice)  must  be  ignited  very 
gently.  The  remarks  made  in  §  101,  2,  #,  in  reference  to  the 
accuracy  of  the  results,  apply  equally  here.  By  way  of  control,  the 
calcium  carbonate  may  be  converted  into  oxide  or  into  calcium 
sulphate  (see  5,  <*),  or  it  may  be  determined  alkalimetrically  (§  198). 


*  Chem.  Centralblatt,  1856,  316. 


;>  104.]  MAGNESIUM.  237 

§104. 

4.  MAGNESIUM. 

a.  Solution. 

Many  magnesium  salts  are  soluble  in  water ;  those  which  are 
insoluble  in  that  menstruum  dissolve  in  hydrochloric  acid,  with  the 
exception  of  some  silicates  and  aluminates. 

I.  Determination. 

Magnesium  is  weighed  (§  74)  either  as  sulphate  or  as  pyro- 
phozphate,  or  as  magnesium  oxide.  In  the  form  of  oxide  or  car- 
bonate, it  may  be  determined  also  by  the  alkalimetric  method 
described  in  §  198. 

We  may  convert  into 

1.  MAGNESIUM  SULPHATE. 

a.  Directly.  b.  Indirectly. 

All  magnesium  salts  of  vola-  All  magnesium  salts  soluble 

tile    acids,    provided    no   other     in  water,  and  also  those  which, 

non- volatile  substance   be  pres-     insoluble    in    that    menstruum, 

€ii t.  dissolve    in    hydrochloric    acid, 

with  separation  of  their  acid 
(provided  no  ammonium  salts 
be  present). 

2.  MAGNESIUM  PYROPHOSPHATE. 

All  magnesium  compounds  without  exception. 

3.  MAGNESIUM  OXIDE. 

a.  Magnesium  salts  of  organic  acids,  or  of  readily  volatile  inor- 
ganic oxygen  acids. 

b.  Magnesium  chloride,  and  magnesium  compounds  convertible 
into  that  salt. 

.  The  direct  determination  as  magnesium  sulphate  is  highly 
recommended  in  all  cases  where  it  is  applicable.  The  indirect  con- 
version into  the  sulphate  serves  only  in  the  case  of  certain  separa- 
tions, and  is  hardly  ever  had  recourse  to  where  it  can  possibly  be 
avoided.  The  determination  as  pyrophosphate  is  most  generally 
resorted  to ;  especially  also  in  the  separation  of  magnesium  from 
other  bases.  The  method  based  on  the  conversion  of  magnesium 
chloride  into  oxide  is  usually  resorted  to  only  to  effect  the  separa- 


238  DETERMINATION.  [§  104. 

tion  of  magnesium  from  the  alkali  metals.    Magnesium  phosphates 
are  analyzed  as  §  135  directs. 

1.  Determination  as  Magnesium  Sulphate. 

Add  to  the  solution  excess  of  pure  dilute  sulphuric  acid,  evapo- 
rate to  dryness,  in  a  weighed  platinum  dish,  on  the  water-bath ; 
then  heat  at  lirst  cautiously,  afterwards,  with  the  cover  on  more 
strongly — here  it  is  advisable  to  place  the  lamp  so  that  the  flame 
may  play  obliquely  on  the  cover  from  above — until  the  excess  of 
sulphuric  acid  is  completely  expelled ;  lastly,  ignite  gently  over 
the  lamp  for  some  time;  allow  to  cool,  and  weigh.  Should  no 
fumes  of  hydrated  sulphuric  acid  escape  upon  the  application  of  a 
strongish  heat,  this  may  be  looked  upon  as  a  sure  sign  that  the 
sulphuric  acid  has  not  been  added  in  sufficient  quantity,  in  which 
case,  after  allowing  to  cool,  a  fresh  portion  of  sulphuric  acid  is 
added.  The  method  yields  very  accurate  results.  Care  must  be 
taken  not  to  use  a  very  large  excess  of  sulphuric  acid.  The  resi- 
due must  be  exposed  to  a  moderate  red  heat  only,  and  weighed 
rapidly.  For  the  properties  of  the  residue,  see  §  74. 

2.  Determination  as  Magnesium  Pyrophosphate.. 

The  solution  of  the  magnesium  salt  is  mixed,  in  a  beaker,  with 
ammonium  chloride,  and  ammonia  added  in  slight  excess.  Should 
a  precipitate  form  upon  the  addition  of  ammonia,  this  may  be  con- 
sidered a  sign  that  a  sufficient  amount  of  ammonium  chloride  has 
not  been  used ;  a  fresh  amount  of  that  salt  must  consequently  be 
added,  sufficient  to  effect  the  re-solution  of  the  precipitate  formed. 
The  clear  fluid  is  then  mixed  wTith  a  solution  of  sodium  phosphate 
or  sodium  ammonium  phosphate*  in  excess,  and  the  mixture  stirred, 
taking  care  to  avoid  touching  the  sides  of  the  beaker  with  the  stir- 
ring-rod ;  otherwise  particles  of  the  precipitate  are  apt  to  adhere 
so  firmly  to  the  rubbed  parts  of  the  beaker,  that  it  will  be  found 
difficult  to  remove  them  ;  the  beaker  is  then  covered,  and  allowed 
to  stand  at  rest  for  twelve  hours,  without  warming ;  after  that  time 
the  fluid  is  filtered,  and  the  precipitate  collected  on  the  filter,  the 
last  particles  of  it  being  rinsed  out  of  the  glass  with  a  portion  of 
the  filtrate,  with  the  aid  of  a  feather ;  when  the  fluid  has  completely 
passed  through,  the  precipitate  is  washed  with  a  mixture  of  3  parts 
of  water,  and  1  part  of  solution  of  ammonia  of  0*96  sp.  gr.,  the 

*  According  to  MOHB  (NaNH4H)PO4  is  preferable  to  (Na2H)PO4  as  a  pre- 
cipitant. (See  Zeitschr.  f.  Anal.  Chem.  12,  36.) 


§  104.1  MAGNESIUM.  239 

operation  being  continued  until  a  few  drops  of  the  fluid  passing 
through  the  filter  mixed  with  nitric  acid  and  a  drop  of  silver  nitrate 
show  only  a  very  slight  opalescence. 

The  precipitate  is  now  thoroughly  dried,  and  then  transferred 
to  a  platinum  crucible  (§  53);  the  latter,  with  the  lid  on,  is  exposed 
for  some  time  to  a  very  gentle  heat,  which  is  finally  increased  to 
intense  redness.  The  filter,  as  clean  as  practicable,  is  incinerated 
in  a  spiral  of  platinum  wire,  and  the  ash  transferred  to  the  cru- 
cible, which  is  then  once  more  exposed  to  a  red  heat,  allowed  to 
cool,  and  weighed.  If  the  magnesium  pyrophosphate  is  dark 
colored,  moisten  with  a  few  drops  of  nitric  acid,  warm  till  dry, 
and  ignite  again. 

For  the  properties  of  the  precipitate  and  residue,  see  §  74. 

This  method,  if  properly  executed,  yields  most  accurate  results. 
The  precipitate  must  be  washed  completely,  but  not  over-washed, 
and  the  washing  water  must  always  contain  the  requisite  quantity 
of  ammonia. 

Direct  experiments,  No.  73,  a  and  5,  gave  respectively  100-43 
and  100-30  instead  of  100. 

3.  Determination  as  Magnesium  Oxide. 

a.  In   Magnesium  Salts  of  Organic  or    Volatile   Inorganic 
Acid*. 

The  magnesium  salt  is  gently  heated  in  a  covered  platinum 
crucible,  increasing  the  temperature  gradually,  until  no  more  fumes 
escape ;  the  lid  is  then  removed,  and  the  crucible  placed  in  an 
oblique  position,  with  the  lid  leaning  against  it.  A  red  heat  is 
now  applied,  until  the  residue  is  perfectly  white.  For  the  prop- 
erties of  the  residue,  see  §  74.  The  method  gives  the  more  accu- 
rate results  the  more  slowly  the  salt  is  heated  from  the  beginning. 
Some  loss  of  substance  is  usually  sustained,  owing  to  traces  of  the 
salt  being  carried  off  with  the  empyreumatic  products.  Mag- 
nesium salts  of  readily  volatile  oxygen  acids  (carbonic  acid,  nitric 
acid),  may  be  transformed  into  magnesium  oxide  in  a  similar  way,  by 
simple  ignition.  Even  magnesium  sulphate  loses  the  whole  of  its 
sulphuric  acid  when  exposed,  in  a  platinum  crucible,  to  the  heat 
of  the  gas  blowpipe-flame  (SONNENSCHEIN).  As  regards  small  quan- 
tities of  magnesium  sulphate,  I  can  fully  confirm  this  statement. 

b.  Conversion  of  Magnesium  Chloride  into  Magnesium  Oxide. 
See  ^  153.  4,  y. 


240  DETERMINATION.  [§  105. 

THIRD   GROUP   OF  BASIC  RADICALS. 

AL  UMINI  UM — C  H  ROMIUM (TITANIUM). 

§  105. 

1.  ALUMINIUM. 

a.  Solution. 

Aluminium  compounds  which  are  insoluble  in  water,  dissolve, 
for  the  most  part,  in  hydrochloric  acid.  Native  crystallized  alu- 
minium oxide  (sapphire,  ruby,  corundum,  &c.),  and  many  native 
aluminium  compounds,  and  also  artificially  produced  aluminium 
oxide  after  intense  ignition,  require  fusing  with  sodium  carbonate, 
caustic  potassa,  or  barium  hydroxide,  as  a  preliminary  step  to  their 
solution  in  hydrochloric  acid.  Many  aluminium  compounds  which 
resist  the  action  of  concentrated  hydrochloric  acid,  may  be  decom- 
posed by  protracted  heating  with  moderately  concentrated  sul- 
phuric acid,  or  by  fusion  with  potassium  disulphate ;  e.g.,  common 
clay. 

b.  Determination. 

Aluminium  is  invariably  weighed  as  aluminium  oxide  (§  75). 
The  several  aluminium  salts  are  converted  into  aluminium  oxide, 
either  by  precipitation  as  aluminium  hydroxide,  and  subsequent 
ignition,  or  by  simple  ignition.  Precipitation  as  basic  acetate  or 
basic  formate  is  resorted  to  only  in  cases  of  separation. 

We  may  convert  into 

ALUMINIUM    OXIDE. 

a.  By  Precipitation.  b.  By  Heating  or  Ignition. 

All  aluminium  salts  soluble  a.    All   aluminium   salts   of 

in  water,  and  those  which,  insolu-  readily    volatile    oxygen     acids 

ble  in  that  menstruum,  dissolve  (e.g.,  aluminium  nitrate). 

in  hydrochloric  acid,  with  sepa-  /?.    All   aluminium   salts   of 

ration  of  their  acid.  organic  acids. 

With  regard  to  the  method  a,  it  must  be  remembered  that  the 
solution  must  contain  no  organic  substances,  which  would  inter- 
fere with  the  precipitation — e.g.,  tartaric  acid,  sugar,  &c.  Should 
such  be  present,  the  solution  must  be  mixed  with  sodium  carbo- 
nate and  potassium  nitrate,  evaporated  to  dryness  in  a  platinum 
dish,  the  residue  fused,  then  softened  with  water,  transferred  to  a 


§  105.]  ALUMINIUM.  241 

beaker,  digested  with  hydrochloric  acid,  and  the  solution  filtered, 
and  then,  but  not  before,  precipitated. 

The  methods  £,  a  and  ft,  are  applicable  only  in  cases  where  no 
other  fixed  substances  are  present.  The  methods  of  determining 
aluminium  in  its  combinations  with  phosphoric,  boracic,  silicic,  and 
chromic  acids,  will  be  found  in  Part  II.  of  this  Section,  under  the 
heads  of  these  several  acids. 

Determination  as  Aluminium  Oxide. 

a.  By  Precipitation. 

Mix  the  moderately  dilute  hot  solution  of  the  aluminium  salt, 
in  a  beaker  or  dish,  with  a  tolerable  quantity  of  ammonium  chlo- 
ride, if  that  salt  is  not  already  present ;  add  ammonia  slightly  in 
excess,  boil  gently  till  the  fluid  gives  a  neutral  or  barely  alkaline 
reaction  (the  fluid  adhering  to  the  test  paper  must  be  washed  back). 
The  fluid  must  not  be  heated  too  long,  or  it  may  become  acid 
through  decomposition  of  ammonium  chloride,  and  some  of  the 
precipitate  may  redissolve ;  allow  to  settle ;  then  decant  the  clear 
supernatant  fluid  on  to  a  filter,  taking  care  not  to  disturb  the  pre- 
cipitate ;  pour  boiling  water  on  the  latter  in  the  beaker,  stir,  let 
the  precipitate  subside,  decant  again,  and  repeat  this  operation  of 
washing  by  decantation  a  second  and  a  third  time;  transfer  the 
precipitate  now  to  the  filter,  finish  the  washing  with  boiling  water, 
dry  thoroughly,  ignite  (§  52),  and  weigh.  The  heat  applied  should 
be  very  gentle  at  first,  and  the  crucible  kept  well  covered,  to  guard 
against  the  risk  of  loss  of  substance  from  spirting,  which  is  always 
to  be  apprehended  if  the  precipitate  is  not  thoroughly  dry ;  towards 
the  end  of  the  process  the  heat  should  be  raised  to  intense  redness. 
In  the  case  of  aluminium  sulphate  the  foregoing  process  is  apt  to 
leave  some  sulphuric  acid  in  the  precipitate,  which,  of  course, 
vitiates  the  result.  To  insure  the  removal  of  this  sulphuric  acid, 
the  precipitate  should  be  exposed  for  5—10  min.  to  the  heat  of  the 
gas  blowpipe  flame.  If  there  are  difficulties  in  the  way,  prevent- 
ing this  proceeding,  the  precipitate,  either  simply  washed  or  mod- 
erately ignited,  must  be  re-dissolved  in  hydrochloric  acid  (wliich 
requires  protracted  warming  with  strong  acid),  and  then  precipi- 
tated again  with  ammonia ;  or  the  sulphate  must  first  be  converted 
into  nitrate  by  decomposing  it  with  lead  nitrate,  added  in  very 
slight  excess,  the  excess  of  lead  removed  by  means  of  hydrostil- 
phuric  acid,  and  the  further  process  conducted  according  to  the 


242  DETERMINATION.  [§  106. 

directions  of  a  or  J.  For  the  properties  of  aluminium  hydroxide 
and  ignited  aluminium  oxide,  see  §  75.  The  method,  if  properly 
executed,  gives  very  accurate  results.  But  if  a  considerable  excess 
of  ammonia  is  used,  more  particularly  in  the  absence  of  ammo- 
nium salts,  and  the  liquid  is  filtered  without  boiling  or  long  stand- 
ing in  a  warm  place  to  remove  the  ammonia,  no  trifling  loss  may 
be  incurred.  This  loss  is  the  greater,  the  more  dilute  the  solution, 
and  the  larger  the  excess  of  ammonia.  The  precipitate  cannot 
well  be  sufficiently  washed  on  the  filter  on  account  of  its  gelatinous 
nature ;  on  the  other  hand,  if  it  be  entirely  washed  by  decantation, 
a  very  large  quantity  of  wash-water  must  be  used,  hence  it  is  advis- 
able to  combine  the  two  methods,  as  directed.*  In  case  the  BUNSEN 
filtering  apparatus  is  used  for  washing  aluminium  hydroxide,  for 
which  operation  it  is  particularly  desirable,  the  precipitate  may  be 
brought  into  the  filter  without  washing  by  decantation,  and  may 
be  ignited  without  previous  drying.  See  §  53,  b. 

b.  By  Ignition. 

a.  Aluminium  Salts  of  Volatile  Oxygen  Acids. 
Ignite  the  salt  (or  the  residue  of  the  evaporated  solution)  in  a 
platinum  crucible,  gently  at  first,  then  gradually  to  the  very  high- 
est degree  of  intensity,  until  the  weight  remains  constant.  For 
the  properties  of  the  residue,  see  §  75.  Its  purity  must  be  care- 
fully tested.  There  are  no  sources  of  error. 

ft.  AliwYiinium  Salts  of  Organic  Acids. 
The  same  method  as  described  §  104,  3,  a  (Magnesium). 

§  106. 

2.  CHROMIUM. 

a.  Solution. 

Many  chromic  salts  are  soluble  in  water.  Chromic  hydroxide, 
and  most  of  the  salts  insoluble  in  water,  dissolve  in  hydrochloric 
acid.  Ignition  renders  chromic  oxide  and  many  chromium  salts 
insoluble  in  acids ;  this  insoluble  modification  must  be  prepared  for 

*  [When  a  solution  of  aluminium  hydroxide  in  potassium  or  sodium  hydrox- 
ide is  boiled  with  excess  of  ammonium  chloride,  the  aluminium  separates  com- 
pletely as  a  hydrated  oxide  with  two  mol.  of  water,  which  may  be  washed  with 
comparative  ease.  In  certain  cases,  as  where  aluminium  is  separated  from  ferric 
iron  by  boiling  their  hydroxides  with  soda,  this  fact  may  be  taken  advantage  of. 
LOWE,  Fres.  Zeitschrift,  IV.  315.] 


§  106.]  CHROMIUM.  243 

solution  in  hydrochloric  acid,  by  fusing  with  3  or  4  parts  of  potassa. 
In  the  process  of  fusing  a  small  quantity  of  potassium  chromate  is 
formed  by  the  action  of  air;  this,  however,  can  be  decomposed  by 
heating  with  hydrochloric  acid  with  formation  of  chromic  chloride. 
Addition  of  alcohol  greatly  promotes  the  reduction  to  chromic 
chloride.  Instead  of  this  fusing  with  potassa,  we  frequently  prefer 
to  adopt  a  treatment,  whereby  the  chromium  is  at  once  oxidized 
and  converted  into  an  alkali  chromate  (see  2).  For  the  solution  of 
chromic  iron,  see  §  160. 

b.  Determination. 

Chromium  is  always,  when  directly  determined,  weighed  as 
chromic  oxide.  It  is  brought  into  this  form  either  by  precipitation 
as  hydroxide  and  ignition,  or  by  simple  ignition.  It  may,  how- 
ever, also  be  estimated,  by  conversion  into  chromic  acid,  and  deter- 
mination as  such. 

We  may  convert  into 

1.  CHROMIC  OXIDE. 

a.  By  Precipitation.  b.  By  Ignition. 

All  chromic  salts  soluble  in  a.  All  chromic  salts  of  vola- 
water,  and  also  those  which,  in-  tile  oxygen  acids,  provided  no 
soluble  in  that  menstruum,  dis-  non-volatile  substances  be  pres- 
solve  in  hydrochloric  acid,  with  ent. 

separation  of  their  acid.     Pro-  fi.  Chromic  salts  of  organic 

vided   always   that   no    organic     acids, 
substances  (such  as  tartaric  acid, 
oxalic  acid,  &c.)  which  interfere 
with  the  precipitation  be  present. 

2.  CHROMIC  ACID,  or.  more  correctly  speaking,  ALKALI  CHROMATE. 

Chromic  oxide  and  all  chromic  salts. 

The  methods  of  analyzing  chromic  phosphates,  borates,  silicates, 
and  chromic  chromate,  will  be  found  in  Part  II.  of  this  Section, 
under  the  heads  of  the  several  acids  of  these  compounds. 

1.  Determination  as  Chromic  Oxide. 

a.  By  Precipitation. 

The  solution,  which  must  not  be  too  highly  concentrated,  is 
heated  to  100°  in  a  platinum  or  porcelain  dish.  If  the  precipita- 
tion is  effected  in  a  glass  vessel,  considerable  error  is  caused  by 
contamination  of  the  precipitate  with  silica.  If  porcelain  is  used, 


244  DETERMINATION.  [§  106. 

this  error  is  slight.  Ammonia  is  then  added  slightly  in  excess,  and 
the  mixture  exposed  to  a  temperature  approaching  boiling,  until 
the  fluid  over  the  precipitate  is  perfectly  colorless,  presenting  no 
longer  the  least  shade  of  red ;  let  the  solid  particles  subside,  wash 
three  times  by  decantation,  and  lastly  on  the  filter,  with  hot  water, 
dry  thoroughly,  and  ignite  (§  52).  The  heat  in  the  latter  process 
must  be  increased  gradually,  and  the  crucible  kept  covered,  other- 
wise some  loss  of  substance  is  likely  to  arise  from  spirting  upon 
the  incandescence  of  the  chromic  oxide  which  marks  the  passing  of 
the  soluble  into  the  insoluble  modification.  For  the  properties  of 
the  precipitate  and  residue,  see  §  76.  This  method,  if  properly 
executed,  gives  accurate  results. 

b.  By  Ignition. 

a.  Chromic  salts  of  Volatile  Oxygen  Acids. 
The  same  method  as  described,  §  105,  Z>,  a  (Aluminium). 

1).  Chromic  salts  of  Organic  Acids. 
The  same  method  as  described,  §  104,  3,  a  (Magnesium). 

2.  CONVERSION  OF  CHROMIUM  IN  CHROMIC  COMPOUNDS 
INTO  ALKALI  CHROMATE. 

(For  the  estimation  of  chromic*acid,  see  §  130.) 
The  following  methods  have  been  proposed  with  this  view : — 
a.  The  solution  of  the  chromic  salt  is  mixed  with  solution  of 
potassa  or  soda  in  excess,  until  the  chromic  hydroxide,  which  forms 
at  first,  is  redissolved.  Chlorine  gas  is  then  conducted  into  the 
cold  fluid  until  it  acquires  a  yellowish-red  tint ;  it  is  then  mixed 
with  potassa  or  soda  in  excess,  and  the  mixture  evaporated  to  dry- 
ness  ;  the  residue  is  ignited  in  a  platinum  crucible.  The  whole  of 
the  potassium  (or  sodium)  chlorate  formed  is  decomposed  by  this 
process,  and  the  residue  consists,  therefore,  now  of  an  alkali  chro- 
mate  and  potassium  (or  sodium)  chloride. — (YoHL.) 

1).  Potassium  hydroxide  is  heated  in  a  silver  crucible  to  calm 
fusion ;  the  heat  is  then  somewhat  moderated,  and  the  perfectly 
dry  chromic  compound  projected  into  the  crucible.  When  the 
substance  is  thoroughly  moistened  with  the  potassa,  small  lumps  of 
fused  potassium  chlorate  are  added.  A  lively  effervescence  ensues, 
from  the  escape  of  oxygen ;  at  the  same  time  the  mass  acquires  a 
more  and  more  yellow  color,  and  finally  becomes  clear  and  trans- 
parent. Loss  of  substance  must  be  carefully  guarded  against  (II. 

SCHWABZ). 


§  107.]  TITANIUM.  245 

c.  Dissolve  chromic  hydroxide  in  solution  of  potassa  or  soda, 
add  lead  dioxide  in  sufficient  excess,  and  warm.  The  yellow  fluid 
produced  contains  all  the  chromium  as  lead  chromate  in  alkaline 
solution.  Filter  from  the  excess  of  lead  dioxide,  add  to  the  filtrate 
acetic  acid  to  acid  reaction,  and  determine  the  weight  of  the  pre- 
cipitated lead  chromate  (G.  CHANCEL*). 

\<L  Render  the  solution  of  chromic  salt  nearly  neutral  by  a 
solution  of  sodium  carbonate,  add  sodium  acetate  in  excess,  heat 
and  add  chlorine  water,  or  pass  in  chlorine  gas,  keeping  the  solu- 
tion nearly  neutral  by  occasional  addition  of  sodium  carbonate. 
The  oxidation  proceeds  readily.  Boil  off  excess  of  chlorine,  when 
the  chromic  acid  may  be  precipitated  as  lead  chromate  or  barium 
chromate  (W. 


§  107. 

Supplement  to  the  Third  Group. 
TITANIUM. 

Titanium  is  always  weighed  as  titanic  oxide  (TiO2),  i.e.,  the 
oxide  or  anhydride  corresponding  to  titanic  acid  (Ti(OH)4). 
Titanic  acid  is  precipitated  with  an  alkali  or  by  boiling  its  dilute 
acid  solution.  In  precipitating  acid  solutions  of  titanic  acid  ammo- 
nia is  employed;  take  care  to  add  the  precipitating  agent  only 
in  slight  excess,  let  the  precipitate  formed,  which  resembles  alu- 
minium hydroxide,  deposit,  wash,  first  by  decantation,  then  com- 
pletely on  the  filter,  dry,  and  ignite  (§  52).  If  the  solution  con- 
tained sulphuric  acid,  put  some  ammonium  carbonate  into  the 
crucible,  after  the  first  ignition,  to  secure  the  removal  of  every 
remaining  trace  of  that  acid.  Lose  no  time  in  weighing  the  ignited 
titanic  oxide,  as  it  is  slightly  hygroscopic.  Occasionally  it  is  more 
convenient  to  precipitate  titanic  acid  from  its  acid  solutions  by 
nearly  neutralizing  with  ammonia,  adding  sodium  acetate  and  boil- 
ing. The  precipitate  thus  obtained  is  easily  filtered  and  washed. 
If  we  have  titanic  acid  dissolved  in  sulphuric  acid,  as  for  instance 
occurs  when  we  fuse  it  with  potassium  disulphate  and  treat  the 
mass  writh  cold  water,  we  may,  by  largely  diluting,  and  long  boil- 
ing, with  renewal  of  the  evaporating  water,  fully  precipitate  the 
titanic  acid.  If  much  free  acid  is  present  it  must  be  nearly  neu- 

*  Comp.  rend.  43,  927.  f  [Am-  Journ.  Sci.  2  Ser.  39,  58.] 


246  DETERMINATION.  [§  107. 

tralized  with  ammonia  before  boiling.  In  the  process  of  igniting 
the  dried  precipitate,  some  ammonium  carbonate  is  added.  From 
dilute  hydrochloric  acid  solutions  of  titanic  acid,  the  latter  sepa- 
rates completely  only  upon  evaporating  the  fluid  to  dryness ;  and 
if  the  precipitate  in  that  case  were  washed  with  pure  water,  the 
filtrate  would  be  milky ;  acid  must,  therefore,  be  added  to  the 
water. 

Titanic  acid  precipitated  in  the  cold,  washed  with  cold  water, 
and  dried  without  elevation  of  temperature,  is  completely  soluble 
in  hydrochloric  acid  ;  otherwise  it  dissolves  only  incompletely  in 
that  acid.  The  metatitanw  acid  thrown  down  from  dilute  acid 
solutions  by  boiling,  is  not  soluble  in  dilute  acids.  Titanic  oxide 
resulting  from  ignition  of  titanic  or  metatitanic  acid  does  not  dis- 
solve even  in  concentrated  hydrochloric  acid,  but  it  does  dissolve 
by  long  heating  with  tolerably  concentrated  sulphuric  acid.  The 
easiest  way  of  effecting  its  solution  is  to  fuse  it  for  some  time  with 
potassium  disulphate,  and  treat  the  fused  mass  with  a  large  quan- 
tity of  cold  water.  Upon  fusing  with  sodium  carbonate,  sodium 
titanate  is  formed,  which,  when  treated  with  water,  leaves  acid 
sodium  titanate,  which  is  soluble  in  hydrochloric  acid.  Titanic 
oxide  (TiOa)  consists  of  60*98  per  cent,  of  titanium,  and  39-02  per 
cent,  of  oxygen.  By  fusing  titanic  oxide  with  three  times  it  quan- 
tity of  potassium  hydrogen  fluoride,  potassium  titanium  fluoride  is 
formed,  which  readily  dissolves  in  very  dilute  hydrochloric  acid 
(of  sp.  gr.  1/015)  in  the  heat.  On  fusing  a  very  low  heat  must  be 
applied  at  first,  till  the  excess  of  hydrofluoric  acid  has  escaped,  then 
the  heat  is  quickly  raised  till  the  mass  melts  and  the  titanic  oxide 
is  just  dissolved  (MARTGNAC*).  On  heating  with  hydrofluoric  and 
sulphuric  acids  practically  no  titanium  fluoride  escapes,  but  by 
heating  with  hydrofluoric  acid  some  loss  does  occur  ( 


Zeitschr.  f.  anal.  Chem.  7,  112.  \  Ib.  2,  71. 


§  108.  |  ZINC.  247 

FOURTH   GROUP  OF   BASIC   RADICALS. 

ZINC MANGANESE NICKEL COBALT — FERROUS   IRON FERRIC   IRON 

— (URANIUM  AND  URANYL). 

§108. 

1.  ZINC. 

a,.  Solution. 

Many  of  the  zinc  salts  are  soluble  in  water.  Metallic  zinc,  zinc 
oxide,  and  the  salts,  which  are  insoluble  in  water,  dissolve  in  hydro- 
chloric acid. 

b.  Determination. 

Zinc  is  weighed  either  as  oxide  or  as  sulphide  (§  77).  The 
conversion  of  zinc  salts  into  the  oxide  is  effected  either  by  precipi- 
tation as  basic  zinc  carbonate  or  sulphide,  or  by  direct  ignition. 
Besides  these  gravimetric  methods,  several  volumetric  methods  are 
in  use. 

We  may  convert  into 

1.  ZINC  OXIDE. 

a.  By  Precipitation  as  Zinc  b.  By  Precipitation  as  Zinc 
Carbonate.  Sulphide. 

All  zinc  salts  which  are  solu-  All  compounds  of  zinc  with- 

ble  in  water,  and  all  zinc  salts  of  out  exception. 
organic  volatile  acids;  also  those 
salts  of  zinc  which,  insoluble  in 
water,  dissolve  in  hydrochloric 
acid,  with  separation  of  their 
acid. 

c.  By  direct  Ignition. 

Zinc  salts  of  volatile  inorganic  oxygen  acids. 

2.  ZINC  SULPHIDE. 

All  compounds  of  zinc  without  exception. 

The  method  1,  £,  is  to  be  recommended  only,  as  regards  the 
more  frequently  occurring  compounds  of  zinc,  for  the  carbonate 
and  the  nitrate.  The  methods  1,  &,  or  2,  are  usually  only  resorted 
to  in  cases  where  1, «,  is  inadmissible.  They  serve  more  especially 
to  separate  zinc  from  other  basic  radicals.  Zinc  salts  of  organic 


248  DETERMINATION.  [§  108. 

acids  cannot  be  converted  into  the  oxide  by  ignition,  since  this 
process  would  cause  the  reduction  and  volatilization  of  a  small  por- 
tion of  the  metal.  If  the  acids  are  volatile,  the  zinc  may  be  deter- 
mined at  once,  according  to  method  1,  a:  if,  on  the  contrary,  the 
acids  are  non- volatile,  the  zinc  is  best  precipitated  as  sulphide.  For 
the  analysis  of  zinc  chromate,  phosphate,  borate,  and  silicate,  look 
to  the  several  acids.  The  volumetric  methods  are  chiefly  employed 
for  technical  purposes ;  see  Special  Part. 

1.  Determination  as  Zinc  Oxide. 

a.  By  Precipitation  as  Zinc  Carbonate, 

Heat  the  moderately  dilute  solution  nearly  to  boiling  in  a  capa- 
cious vessel, — a  glass  vessel  is  poorly  adapted  for  this  purpose^ 
porcelain  is  better,  and  platinum  best ; — add,  drop  by  drop,  sodium 
carbonate  till  the  fluid  shows  a  strong  alkaline  reaction ;  boil  a  few 
minutes;  allow  to  subside,  decant  through  a  filter,  and  boil  the 
precipitate  three  times  with  water,  decanting  each  tim'e;  then 
transfer  the  precipitate  to  the  filter,  wash  completely  with  hot 
water,  dry,  and  ignite  as  directed  §  53,  taking  care  to  have  the  filter 
as  clean  as  practicable,  before  proceeding  to  incinerate  it.  Should 
the  solution  contain  ammonium  salts,  the  ebullition  must  be  con- 
tinued until,  upon  a  fresh  addition  of  sodium  carbonate,  the  escap- 
ing vapor  no  longer  imparts  a  brown  tint  to  turmeric  paper.  If 
the  quantity  of  ammonium  salts  present  is  considerable",  the  fluid 
must  be  evaporated  boiling  to  dryness.  It  is,  therefore,  in  such 
cases  more  convenient  to  precipitate  the  zinc  as  sulphide  (see  b). 

The  presence  of  a  great  excess  of  acid  in  the  solution  of  zinc 
must  be  as  much  as  possible  guarded  against,  that  the  effervescence 
from  the  escaping  carbonic  acid  gas  may  not  be  too  impetuous.  The 
filtrate  must  always  be  tested  with  ammonium  sulphide  (with  addi- 
tion of  ammonium  chloride)  to  ascertain  whether  the  whole  of  the 
zinc  has  been  precipitated ;  a  slight  precipitate  will  indeed  invariably 
form  upon  the  application  of  this  test ;  but,  if  the  process  has  been 
properly  conducted,  this  is  so  insignificant  that  it  may  be  altogether 
disregarded,  being  limited  to  some  exceedingly  slight  and  impon- 
derable flakes,  which  moreover  make  their  appearance  only  after 
many  hours'  standing.  If  the  precipitate  is  more  considerable, 
however,  it  must  be  treated  as  directed  in  5,  and  the  weight  of  the 
zinc  oxide*  obtained  added  to  that  resulting  from  the  first  process. 
For  the  properties  of  the  precipitate  and  residue,  see  §  77.  This 


§  108.]  ZINC.  249 

method  yields  pretty  accurate  results,  though  they  are  in  most 
cases  a  little  too  low,  as  the  precipitation  is  never  absolutely  com- 
plete, and  as  particles  of  the  precipitate  will  always  and  unavoid- 
ably adhere  to  the  filter,  which  exposes  them  to  the  chance  of 
reduction  and  volatilization  during  the  process  of  ignition.  On 
the  other  hand,  the  results  are  sometimes  too  high ;  this  is  owing 
to  defective  washing,  as  may  be  seen  from  the  alkaline  reaction 
which  the  residue  manifests  in  such  cases.  It  is  advisable  also  to 
ascertain  whether  the  residue  will  dissolve  in  hydrochloric  acid 
without  leaving  silica;  this  latter  precaution  is  indispensable  in 
cases  where  the  precipitation  has  been  effected  in  a  glass  vessel. 

[It  is  often  better,  especially  in  presence  of  ammonium  salts,  to 
heat  the  dry  zinc  salt  with  excess  of  sodium  carbonate  in  a  plati- 
num dish  cautiously  to  near  redness,  then  treat  with  hot  water  and 
wash  as  directed.] 

b.  By  Precipitation  as  Zinc  Sulphide. 

Mix  the  solution,  contained  in  a  not  too  large  flask  and  suffi- 
ciently diluted,  with  ammonium  chloride,  then  add  ammonia,  till 
the  reaction  is  just  alkaline,  and  then  colorless  or  slightly  yellow 
ammonium  sulphide  in  moderate  excess.  If  the  flask  is  not  now 
quite  full  up  to  the  neck,  make  it  so  with  water,  cork,  allow  to 
stand  12  to  24  hours  in  a  warm  place,  wash  the  precipitate,  if  con- 
siderable, first  by  decantation,  then  on  the  filter  with  water  con- 
taining ammonium  sulphide  and  also  less  and  less  ammonium  chlo- 
ride (finally  none).  In  decanting  do  not  pour  the  fluid  through  the 
filter,  but  at  once  into  a  flask.  After  thrice  decanting,  filter  the 
fluid  that  was  poured  off,  and  then  transfer  the  precipitate  to  the 
filter,  finishing  the  washing  as  directed.  The  funnel  is  kept  cov- 
ered with  a  glass  plate.  If  the  zinc  is  not  to  be  determined  accord- 
ing to  2,  then  put  the  moist  filter  with  the  precipitate  in  a  beaker, 
and  pour  over  it  moderately  dilute  hydrochloric  acid  slightly  in 
excess.  Put  the  glass  now  in  a  warm  place,  until  the  solution 
smells  no  longer  of  hydrogen  sulphide ;  dilute  the  fluid  with  a  little 
water,  filter,  wash  the  original  filter  with  hot  water,  and  proceed 
with  the  solution  of  zinc  chloride  obtained  as  directed  in  a. 

The  following  method  also  effects  a  practically  complete  pre- 
cipitation of  zinc  from  acid  solution.  Add  sodium  carbonate,  at 
last  drop  by  drop  till  a  lasting  precipitate  forms,  dissolve  the  latter 
by  a  drop  of  hydrochloric  acid,  pass  hydrogen  sulphide  till  the 


250  DETERMINATION.  [§  108. 

precipitate  ceases  to  increase  perceptibly,  add  sodium  acetate,  and 
again  pass  the  gas.  After  washing  with  water  containing  hydro- 
gen sulphide  (which  when  the  zinc  sulphide  had  been  thrown 
down  by  hydrogen  sulphide  from  acetic  acid  solution,  is  easily 
done),  treat  as  above  directed. 

From  a  solution  of  zinc  acetate  the  metal  may  be  precipitated 
completely,  or  nearly  so,  with  hydrogen  sulphide  gas,  even  in  pres- 
ence of  an  excess  of  acetic  acid,  provided  always  no  other  free 
acid  be  present  (Expt.  Xo.  74)..  The  precipitated  zinc  sulphide  is 
washed  with  water  impregnated  with  hydrogen  sulphide,  and,  for 
the  rest,  treated  exactly  like  the  zinc  sulphide  obtained  by  precipi- 
tation with  ammonium  sulphide. 

Small  quantities  of  zinc  sulphide  may  also  be  converted  directly 
into  the  oxide,  by  heating  in  an  open  platinum  crucible,  to  gentle 
redness  at  first,  then,  after  some  time,  to  most  intense  redness. 

c.  By  direct  Ignition. 

The  salt  is  exposed,  in  a  covered  platinum  crucible,  first  to  a 
gentle  heat,  finally  to  a  most  intense  heat,  until  the  weight  of  the 
residue  remains  constant.  The  action  of  reducing  gases  is  to  be 
avoided. 

2.  Determination  as  Zinc  Sulphide. 

The  precipitated  zinc  sulphide,  obtained  as  in  1,  J,  may  be 
ignited  in  hydrogen  and  weighed.  H.  ROSE,*  who  has  lately 
recommended  the  process,  employs  the  apparatus  represented  by 
%  50. 

a  contains  concentrated  sulphuric  acid,  b,  calcium  chloride. 
The  porcelain  crucible  has  a  perforated  porcelain  or  platinum 
cover,  into  the  opening  of  which  fits  the  porcelain  or  platinum 
tube,  d.  The  latter  is  provided  with  an  annular  projection  which 
rests  on  the  cover,  the  tube  itself  extends  some  distance  into  the 
crucible.  When  the  zinc  sulphide  has  dried  in  the  filter,  it  is 
transferred  to  the  weighed  porcelain  crucible,  the  filter  ashes  added, 
powdered  sulphur  is  sprinkled  over  the  contents  of  the  crucible, 
the  cover  is  placed  on,  and  hydrogen  is  passed  in  a  moderate 
stream,  a  gentle  heat  is  applied  at  first,  which  is  afterwards  raised 
for  five  minutes  to  intense  redness ;  finally  the  crucible  is  allowed 
to  cool  with  continued  transmission  of  the  gas,  and  the  zinc  sul- 
phide is  weighed. 

*  Pogg.  Anal.  110,  128. 


§  109.] 


MANGANESE. 


251 


[Instead  of  the  porcelain  tube  and  perforated  cover,  a  common 
tobacco-pipe  may  be  employed,  the  bowl  of  the  latter  being  inverted 
over  or  within  a  porcelain  crucible.  Hydrogen  sulphide  may  be 
advantageously  substituted  for  hydrogen.] 

OESTEN'S  experiments,  which  were  adduced  by  ROSE  in  support 
of  the  accuracy  of  this  method,  were  highly  satisfactory. 

Zinc  sulphate,  carbonate,  and  oxide  may  be  converted  into  sul- 
phide in  the  manner  just  described.  They  must,  however,  be 
mixed  with  an  excess  of  powdered  sulphur,  otherwise  you  will  lose 
some  zinc  from  the  reducing  action  of  the  hydrogen  (H.  ROSE.) 


.      Fig.  50. 

The  properties  of  the  hydrated  and  anhydrous  zinc  sulphide  are 
given  §  77 ;  the  results  are  accurate.  Loss  occurs  only  when  the 
ignition  is  performed  over  the  gas  blowpipe  (which  is  quite  unnec- 
essary), and  continued  longer  than  five  minutes.  Compare  §  77,  c. 

§  109. 

2.  MANGANESE. 

a.  Solution. 

Many  manganous  salts  are  soluble  in  water.  The  manganous 
salts  which  are  insoluble  in  that  menstruum,  dissolve  in  hydrochloric 
acid,  which  dissolves  also  all  oxides  of  manganese.  The  solution 


252  DETERMINATION.  [§  109. 

of  the  higher  oxides  is  attended  with  evolution  of  chlorine — equiva- 
lent to  the  amount  of  oxygen  which  the  oxide  under  examination 
contains,  more  than  manganous  oxide  (MnO) — and  the  fluid,  after 
application  of  heat,  is  found  to  contain  manganous  chloride. 

b.  Determination. 

Manganese  is  weighed  either  as  protosesquioxide,  as  sulphide,. 
or  as  pyrop hosphate  (§  78).  Into  the  form  of  protosesquioxide  it 
is  converted  either  by  precipitation  as  manganous  carbonate,  or 
as  manganous  hydroxide,  sometimes  preceded  by  precipitation  a& 
manganous  sulphide,  or  as  manganese  dioxide ;  or,  iinally,  by  direct 
ignition.  [When  determined  as  pyrophosphate  it  is  precipitated 
as  ammonium  manganous  phosphate.] 

Manganese  may  be  determined  volumetrically  in  two  different 
ways,  one  being  applicable  to  any  manganous  solution,  provided  it 
be  free  from  any  other  substance  which  exerts  a  reducing  action 
on  alkaline  solution  of  potassium  ferricyanide,  the  other  being  only 
admissible,  when  we  have  manganese  in  the  condition  of  a  perfectly 
definite  higher  oxide,  and  free  from  other  bodies,  which  evolve 
chlorine  on  boiling  with  hydrochloric  acid. 

We  may  convert  into 

1.  MANGANESE  PROTOSESQUIOXIDE. 

a.  By  Precipitation  as  Man-        b.  By  Precipitation  as  Man- 
ganous Carbonate.  ganese  Hydroxide. 

All   soluble   manganous  salts         All  the  compounds  of  manga- 
of  inorganic  acids,  and  all  man-     nese,  with  the  exception  of  its 
ganous  salts  of  volatile  organic     salts  of  non-volatile  organic  acids, 
acids  ;  also  those  manganous  salts 
which,  insoluble   in  water,  dis- 
solve in  hydrochloric  acid  with 
separation  of  their  acid. 

c.  By  Precipitation  as  Man-        d.  By  Separation  as  Manga- 
ganese  Sulphide.  nese  Dioxide. 

All  compounds  of  manganese         All  compounds  of  manganese 
without  exception.  in  a  slightly  acid  solution,  espe- 

cially manganous  acetate  and  ni- 
trate. 

e.  By  direct  Ignition. 

All  manganese  oxides ;  man- 
ganous salts  of  readily  volatile 
acids,  and  organic  acids. 


g  109.]  MANGANESE.  253 

2.  MANGANESE  SULPHIDE. 

All  compounds  of  manganese  without  exception. 

3.  MANGANESE  PYROPHOSPHATE. 

All  the  oxides  of  manganese  and  many  manganous  salts. 

The  method  1,  <?,  is  simple  and  accurate,  but  seldom  admissible. 
The  method  1,  a,  is  the  most  usually  employed ;  if  one's  choice  is 
free,  it  is  to  be  preferred  to  1,  b.  The  methods  1,  e,  and  2,  are 
generally  used,  when  the  methods  1,  «,  or  £,  cannot  be  adopted- 
say  on  account  of  the  presence  of  a  non- volatile  organic  substance, 
and  also  when  we  have  to  separate  manganese  from  other  metals. 
The  latter  object  may  be  attained  also  by  the  method  1,  d.  The 
process  3,  is  very  convenient  and  accurate  in  absence  of  alkali-earth 
metals,  and  heavy  metals.  Manganous  phosphate  and  borate  are 
treated,  either  according  to  the  method  1,  J,  as  the  salts  precipi- 
tated from  acid  solution  by  potassa  are  completely  decomposed  upon 
boiling  with  excess  of  potassa,  or  according  to  the  method  2.  In 
-ilicates  the  manganese  is  determined  after  the  separation  of  the 
silicic  acid  (§  140),  according  to  1,  a,  or  3  ;  for  the  analysis  of  man- 
ganous chromate,  see  §  130  (chromic  acid).  The  volumetric 
method  by  reduction  of  potassium  ferricyanide  is  especially  suited 
for  technical  work,  in  which  the  highest  degree  of  accuracy  is  not 
required.  The  estimation  of  manganese  from  the  quantity  of  chlo- 
rine disengaged  upon  boiling  the  oxides  with  hydrochloric  acid,  is 
resorted  to,  more  particularly,  to  determine  the  degrees  of  oxidation 
of  manganese,  and  permits  also  the  estimation  of  manganese  in 
presence  of  other  metals  (see  Section  V.). 

1.  Determination  as  Protosesquioxide  of  Manganese. 

a.  By  Precipitation  as  Manganous  Carbonate. 

The  precipitation  and  washing  are  effected  in  exactly  the  same 
way  as  directed  §  108,  1,  a  (determination  of  zinc  as  oxide,  by 
precipitation  as  carbonate).  If  the  filtrate  is  not  absolutely  clear, 
stand  it  in  a  warm  place  for  twelve  to  twenty-four  hours.  A  slight 
precipitate  will  then  separate,  which  is  collected  on  another  small 
filter.  The  precipitate  is  dried,  and  then  ignited  as  directed 
|  53.  The  lid  is  removed  from  the  crucible,  and  a  strong  heat 
maintained  until  the  weight  of  the  residue  remains  constant.  Care 
must  be  taken  to  prevent  reducing  gases  finding  their  way  into  the 
crucible.  For  the  properties  of  the  precipitate  and  residue,  see 
§  78.  This  method,  if  properly  executed,  gives  accurate  results. 


254  DETERMINATION.  [§  109. 

The  principal  point  is  to  continue  the  application  of  a  sufficiently 
intense  heat  long  enough  to  effect  the  object  in  view.  It  is  neces- 
sary also  to  ascertain  whether  the  residue  has  not  an  alkaline  reac- 
tion,'and  having  removed  it  from  the  platinum  crucible,  whether 
it  dissolves  in  hydrochloric  acid  without  leaving  silica. 

b.  By  Precipitation  as  Manganous  Hydroxide. 

The  solution  should  not  be  too  concentrated,  and  it  is  best  to 
have  it  in  a  platinum  dish.  Precipitate  with  solution  of  pure 
soda  or  potassa,  and  proceed  in  all  other  respects  as  in  a. 

If  phosphoric,  acid  is  present,  or  boracic  acid,  the  fluid  must  be 
kept  boiling  for  some  time  with  an  excess  of  alkali.  For  the  prop- 
erties of  the  precipitate,  see  §  78. 

c.  By  Precipitation  as  Manganese  Sulphide. 

The  solution  contained  in  a  comparatively  small  flask  and  not 
too  dilute  is  first  mixed  with  ammonium  chloride  (if  an  ammonium 
salt  is  not  already  present  in  sufficient  quantity),  then — if  the  fluid 
is  acid — with  ammonia,  till  it  reacts  neutral  or  very  slightly  alka 
line ;  now  add  yellow  ammonium  sulphide,  in  moderate  excess,  if 
the  flask  is  not  already  quite  full  up  to  the  neck,  add  water  till 
it  is,  cork,  stand  it  in  a  warm  place  for  at  least  twenty-four  hours, 
wash  the  precipitate  if  at  all  considerable,  first  by  decantation,  then 
on  the  filter,  using  water  containing  ammonium  sulphide,  and  also 
gradually-diminished  quantities  of  ammonium  chloride  (finally 
none).  In  decanting,  pour  the  fluid  in  a  flask,  not  on  the  filter. 
After  decanting  three  times,  filter  the  fluids  that  have  been  poured 
off,  transfer  the  precipitate  to  the  filter,  and  finish  the  washing  as 
above  directed,  without  interruption.  Keep  the  funnel  covered 
with  a  glass  plate.  If  you  do  not  prefer  to  determine  according  to 
2,  proceed  as  follows : — Put  the  moist  filter  with  the  precipitate 
into  a  beaker^  add  hydrochloric  acid,  and  warm  until  the  mixture 
smells  no  longer  of  hydrogen  sulphide ;  filter,  wash  the  residuary 
paper  carefully,  and  precipitate  the  filtrate  as  directed  in  a.  The 
results  are  satisfactory,  compare  §  78,  e. 

Tartaric  acid  retards  the  precipitation,  but  does  not  render  it 
less  complete ;  citric  acid  prevents  precipitation,  or  at  least  makes 
it  incomplete. 

d.  By  Separation  as  Manganese  Dioxide. 

Heat  the  solution  of  rnanganous  acetate  or  some  other  manga 
nous  salt  containing  but  little  free  acid,  after  addition  of  a  sufficient 


§  1.09.]  MANGANESE.  255 

quantity  of  sodium  acetate,  to  from  50°  to  60°,  and  transmit  chlo- 
rine gas  through  the  fluid,  or  add  bromine  (KAMMERER,*  A\rAAGEf). 
The  whole  of  the  manganese  present  falls  down  as  dioxide  (SCHIEL, 
RIVOT,  BKUDAXT.  and  DAGUIX).  Wash,  first  by  decantation,  then 
upon  the  filter ;  dry,  transfer  the  precipitate  to  a  flask,  add  the  filter 
ash,  heat  with  hydrochloric  acid,  filter,  and  precipitate  as  directed 
in  a.  If  the  sodium  acetate  is  deficient,  and  especially  if  hydro- 
chloric acid  is  present,  it  may  happen  that  the  precipitation  of  the 
manganese  by  chlorine  or  bromine  is  not  quite  complete ;  it  is 
therefore  well,  after  filtering  off  the  dioxide,  to  treat  the'  filtrate 
with  more  sodium  acetate,  and  again  pass  chlorine  or  add  bromine. 
The  separation  of  manganese  as  dioxide,  by  evaporating  its  solution 
in  nitric  acid  to  dryness,  and  heating  the  residue,  finally  to  155°,  is 
given  m  Section  V. 

e.  By  direct  Ignition. 

The  manganese  compound  under  examination  is  introduced 
into  a  platinum  crucible,  which,  is  kept  closely  covered  at  first,  and 
exposed  to  a  gentle  heat ;  after  a  time  the  lid  is  taken  off,  and 
replaced  loosely  on  the  crucible,  and  the  heat  is  increased  to  the 
highest  degree  of  intensity,  with  careful  exclusion  of  reducing 
gases ;  the  process  is  continued  until  the  weight  of  the  residue 
remains  constant.  The  conversion  of  the  higher  oxides  of  manga- 
nese into  protosesquioxide  of  manganese  requires  more  protracted 
and  intense  heating  than  the  conversion  of  manganous  oxide.  In 
fact,  it  can  hardly  be  effected  without  the  use  of  a  gas  blowpipe. 
In  the  case  of  manganous  salts  of  organic  acids,  care  must  always 
be  taken  to  ascertain  whether  the  whole  of  the  carbon  has  been 
consumed;  and  should  the  contrary  turn  out  to  be  the  case  "the 
residue  must  either  be  dissolved  in  hydrochloric  acid,  and  the  solu 
tion  precipitated  as  directed  in  «,  or  3,  or  it  must  be  repeatedly 
evaporated  with  nitric  acid,  until  the  whole  of  the  carbon  is 
oxidized.  The  method,  if  properly  executed,  gives  accurate  results. 
On  the  other  hand,  if  the  directions  are  not  carefully  attended  to, 
one  must  not  be  surprised  at  considerable  differences.  In  the  igni- 
tion of  manganous  salts  of  organic  acids,  minute  particles  of  the 
salt  are  generally  carried  away  with  the  empyreumatic  products 
evolved  in  the  process,  which,  of  course,  tends  to  "reduce  the  weight 
a  little. 


*  Ber.  der  deutsch.  Chem.  Gesellsch.  4.  218. 
f  Zeitschr.  f  anal.  Chem  10.  206. 


256  DETERMINATION.  [§  109. 

2.  Determination  as  Manganous  Sulphide. 

The  sulphide  precipitated  as  in  1,  c7  may  be  determined  in  this 
form,  as  follows  :  Dry,  transfer  the  precipitate  to  a  crucible,  burn 
the  filter,  add  the  ashes,  strew  some  sulphur  on  the  top,  ignite 
strongly  in  hydrogen  (till  it  becomes  black)  and  weigh  as  anhy- 
drous manganous  sulphide  (H.  ROSE*),  compare  the  analogous 
process  for  zinc,  §  108,  2. 

The  results  obtained  by  OESTEN,  and  cited  by  ROSE,  are  per- 
fectly satisfactory. 

This  method  is  shorter  and  more  convenient  than  dissolving 
the  moist  sulphide  in  hydrochloric  acid,  and  precipitating  with 
sodium  carbonate. 

Manganous  sulphate  and  all  the  oxides  of  manganese  may  be 
subjected  to  this  process  with  the  same  result. 

[3.  Determination  as  Manganous  Pyrophosphate. 

To  the  solution  of  the  manganous  salt,  which  may  contain 
ammonium  or  alkali  salts,  sodium  phosphate  is  added  in  large 
excess  above  what  is  needful  to  convert  the  manganese  into  phos- 
phate. The  white  precipitate  which  is  formed  unless  considerable 
free  acid  is  already  present  is  then  redissolved  in  sulphuric  or 
chlorhydric  acid,  the  liquid  is  heated  to  boiling,  best  in  a  platinum 
dish,  and  ammonia  added  in  excess.  The  boiling  is  continued  10 
—15  minutes,  whereby  the  white,  semi-gelatinous  precipitate  first 
formed  is  converted  into  rose-colored,  pearly  scales.  If  one  is 
obliged  to  precipitate  in  a  glass  beaker  the  precipitate  may  be  con- 
verted into  the  crystalline  form  more  safely  by  heating  on  the 
water-bath  1  or  2  hours,  as  it  is  likely  to  be  thrown  out  of  the 
beaker  by  boiling.  The  whole  is  kept  hot  for  an  hour  longer, 
then  filtered  and  washed  with  water  containing  a  little  ammonia. 
The  precipitate  of  ammonium  manganous  phosphate  is  dried,  sepa- 
rated from  the  filter,  and  converted  by  ignition  into  pyrophos- 
phate.  See  §  78  (GriBBS,f  HENEY^).] 

It  is  advantageous  to  use  the  Bunsen  filtering  apparatus  for 
washing  the  precipitate  on  account  of  its  slight  solubility  in  water. 
(See  §  78,  g.)  For  the  same  reason  when  great  accuracy  is  required 
it  is  recommended  to  evaporate  the  filtrate  to  dryness,  redissolve 
with  water  and  hydrochloric  acid,  make  alkaline  with  ammonia, 

*  Pogg.  Anal.  110,  122.  f  Am.  Jour.  Sci.  2d  Ser.  44,  p.  216. 

t  Ib.  47,  p.  130. 


§  109.]  MANGANESE.  257 

and  boil  to  precipitate  and  recover  the  small  amount  of  manganese 
which  may  have  passed  into  the  filtrate. 

4.   Volumetric  determination  by  the  Reduction  of  Ferri- 
cyanide  of  Potassium  (E.  LENSSEN*). 

The  method  is  grounded  on  the  fact  that  if  a  solution  of  a 
manganous  salt  is  acted  on  by  excess  of  alkaline  solution  of  potas- 
sium ferricyanide  at  a  boiling  temperature  in  the  presence  of  a 
sufficient  amount  of  a  ferric  salt,  all  the  manganese  is  precipitated 
as  dioxide,  while  a  corresponding  quantity  of  potassium  f  errocyanide 
is  formed.  By  determining  the  latter,  the  amount  of  manganese 
present  is  obtained. 

K6FeaCy12+2K20  +  MnSO4=2K4FeCy8  +  K2SO4  +  MnO,. 

Accordingly  1  at.  manganese  gives  rise  to  2  mol.  potassium 
f  errocyanide.  Of  course  all  other  reducing  substances  must  be 
absent,  and  the  manganese  must  be  present  entirely  in  the  form  of 
a  manganous  salt.  If  the  solution  contains  no  ferric  salt,  the  pre- 
cipitate is  a  combination  of  much  dioxide,  with  little  manganous 
oxide,  not  always  in  the  same  proportions.  In  performing  the 
process,  mix  first  with  the  acid  solution  of  the  manganous  salt  so 
much  ferric  chloride  that  you  may  be  sure  of  having  at  least  1 
mol.  Fe,Cl8  to  1  atom  Mn,  and  add  the  mixture  gradually  to  a 
boiling  solution  of  potassium  ferricyanide,  previously  rendered 
strongly  alkaline  with  potassa  or  soda.  After  boiling  together  a 
short  time  the  brownish-black  precipitate  becomes  granular  and 
less  bulky.  Allow  to  cool  completely,  filter  off  and  wash  the  pre- 
cipitate, acidify  the  filtrate  with  hydrochloric  acid,  and  estimate 
the  potassium  ferrocyanide  with  permanganate,  according  to  §  147, 
II.,  g.  a.  If  the  liquid  is  filtered  hot,  the  results  are  too  high,  as 
the  filter  in  this  case  has  a  reducing  action.  The  method  may  be 
shortened,  as  follows :  After  boiling,  transfer  the  solution,  together 
with  the  precipitate,  to  a  measuring  flask,  allow  to  cool,  fill  up  to 
the  mark  with  water,  shake,  and  allow  to  settle.  Filter  through  a 
dry  filter,  take  out  a  certain  quantity  with  a  pipette,  and  determine 
the  ferrocyanide  in  this.  A  slight  source  of  error  is  here  intro- 
duced by  disregarding  the  volume  of  the  precipitate.  The  results 
adduced  by  LENSSEN  are  very  satisfactory.  I  have  myself  repeat- 
edly tested  this  method,  and  I  have  to  remark  as  follows : — 

*  Journ.  f.  prakt.  Chcm.  80,  408. 


258  DETERMINATION.  [§  110. 

a.  If  potassium  ferricyanide  is  long  boiled  with  pure  potassa,  a 
small  quantity  of  ferrocyanide  is  invariably  produced. 

b.  The  potassa  must  be  quite  free  from  organic  substances,  and 
should  therefore,  if  there  is  any  doubt  on  this  point,  be  fused  in  a 
silver  dish  before  use,  otherwise  the  error  alluded  to  in  a  may  be 
considerably  increased. 

c.  The    complete  washing   of   the  voluminous    precipitate    is 
attended  with  so  much  difficulty  and  loss  of  time  as  to  render  the 
method  more  troublesome  than  a  gravimetric  analysis. 

d.  The  abridged  method,  on  the  other  hand,  may  be  of  great 
service   in   certain    cases,  especially  when  a  series  of    manganese 
determinations  have  to  be  made,  the  manganese  not  being  in  too- 
minute  quantities,  and  the  highest  degree  of  accuracy  not  being 
required.     In  my  laboratory,  by  employing  a  slight  excess  of  ferric 
salt,  97'9— 100-12— 98-21— 98-99,  and  100-4  were  obtained,  instead 
of  100.     The  inaccuracy  increases  on  using  a  large  excess  of  the 
iron.* 

5.  Volumetric  determination  ~by  boiling  tlie  higher  oxides 
with  hydrochloric  acid,  and  estimating  the  chlorine  evolved. 
The  methods  here  employed  will  be  found  all  together  in  the 
Special  Part  under  "  Valuation  of  Manganese  Ores." 

§  no. 

3.  NICKEL. 

a.  Solution. 

Many  nickelous  salts  are  soluble  in  water.  Those  which  are 
insoluble,  as  also  nickelous  oxide,  in  its  common  modification, 
dissolve,  without  exception,  in  hydrochloric  acid.  The  peculiar 
modification  of  nickelous  oxide,  discovered  by  GENTH,  which  crys- 
tallizes in  octahedra,  does  not  dissolve  in  acids,  but  is  rendered 
soluble  by  fusion  with  potassium  disulphate.  Metallic  nickel  dis- 
solves slowly,  with  evolution  of  hydrogen  gas,  when  warmed  with 
dilute  hydrochloric  or  sulphuric  acid ;  in  nitric  acid,  it  dissolves 
with  great  readiness.  Nickel  sulphide  is  but  sparingly  soluble  in 
hydrochloric  acid,  but  it  dissolves  readily  in  nitrohydrochloric  acid. 
Nickelic  oxide  (Ni2O3)  dissolves  in  hydrochloric  acid,  upon  the 
application  of  heat,  to  nickelous  chloride,  with  evolution  of 
chlorine. 


*  Zeitschr.  f.  Anal.  Chem.  3,  209. 


§  110.  J  NICKEL.  259 

b.  Determination. 

Nickel  is  best  weighed  as  metal ;  it  may  be  weighed  also  as 
nickelous  oxide,  or  sulphate.  The  compounds  of  nickel  are  con- 
verted into  nickelous  oxide,  usually  by  precipitation  as  nickelous 
hydroxide,  preceded,  in  some  instances,  by  precipitation  as  nickel 
sulphide,  or  by  ignition. 

We  may  convert  into 

1.  NICKELOUS  OXIDE. 

a.  By  Precipitation  as  Nick-  b.  By  Precipitation  as  Nick- 
elous Hydroxide.  el  Sulphide. 

All  nickel  salts  of  inorganic  All     compounds    of    nickel 

acids  which  are  soluble  in  water,     without  exception, 
and  all  its  salts  of  volatile  or- 
ganic acids  ;  likewise  all  salts  of 
nickel  which,  insoluble  in  water, 
dissolve  in  the  stronger   acids, 
with  separation  of  their  acid. 
c.  By  Ignition. 

Nickel  salts  of  readily  volatile  oxygen  acids,  or  of 
such  oxygen  acids  as  are  decomposed  at  a  high  tem- 
perature (carbonic  acid,  nitric  acid). 

2.  METALLIC  NICKEL  :    Nickelous   oxide,  also  nickel  chloride, 
bromide,  and  iodide. 

3.  NICKEL  SULPHATE:    Nickel  salts,  whose  acids  are  entirely 
expelled  by  heating  and  evaporating  with  sulphuric  acid. 

The  method  1,  ?,  is  very  good,  but  seldom  admissible.  The 
method  1,  #,  is  most  frequently  employed.  In  the  presence  of 
sugar,  or  other  non-volatile  organic  substance,  it  cannot  be  used. 
Tn  this  case  we  must  either  ignite  and  thereby  destroy  the  organic 
matter  before  precipitating,  or  we  must  resort  to  the  method  £, 
which  otherwise  is  hardly  used  except  in  separations.  By  what- 
ever method  nickelous  oxide  is  obtained,  it  is  best  to  convert  it 
into  metallic  nickel  (by  method  2)  before  weighing.  The  conver- 
sion into  nickel  sulphate  (method  3)  is  quickly  executed,  but  it 
requires  the  greatest  care  to  obtain  trustworthy  results.  Nickel 
salts  of  chromic,  phosphoric,  boracic,  and  silicic  acids  are  analyzed 
according  to  the  methods  given  under  the  several  acids. 


260  DETERMINATION.  [§  110. 

1.  Determination  as  Nickelous  Oxide. 

a.  By  Precipitation  as  Nickelous  Hydroxide. 

Mix  the  solution  with  pure  solution  of  potassa  or  soda  in  excess, 
heat  for  some  time  nearly  to  ebullition,  decant  3  or  4  times,  boiling 
up  each  time,  filter,  wash  the  precipitate  thoroughly  with  hot  water, 
dry  and  ignite  strongly  (avoiding  reducing  gases  if  the  oxide  is  to  be 
weighed)  (RussELi/*)  (§  53).  The  precipitation  is  best  effected  in 
a  platinum  dish ;  in  presence  of  nitrohydrochloric  acid,  or,  if  the 
operator  does  not  possess  a  sufficiently  capacious  dish  of  the  metal, 
in  a  porcelain  dish  ;  glass  vessels  do  not  answer  the  purpose  so  well. 
Presence  of  ammoniacal  salts,  or  of  free  ammonia,  does  not  inter- 
fere with  the  precipitation.  For  the  properties  of  the  precipitate 
and  residue,  see  §  79.  Instead  of  weighing  the  oxide  it  is  better 
to  reduce  it  to  metal  according  to  §  1 1 0,  2.  The  thorough  washing 
of  the  precipitate  is  a  most  essential  point.  It  is  necessary  also  to 
ascertain  whether  the  weighed  metal  (or  oxide)  has  not  an  alkaline 
reaction,  and  whether  it  dissolves  completely  in  nitric  acid  (or 
hydrochloric  in  case  oxide  is  weighed). 

1).  By  Precipitation  as  Sulphide  of  Nickel. 

[a.  Add  to  the  solution,  which  should  be  concentrated,  a  large 
quantity  of  ammonium  chloride.  The  precipitation  is  effected 
more  readily  if  enough  ammonium  chloride  is  present  to  make  the 
solution  nearly  saturated  when  cold.  Make  the  solution  neutral 
or  better  slightly  acid  by  addition  of  ammonia  or  hydrochloric  acid 
as  the  case  demands.  Heat  to  boiling  in  a  flask  and  add  drop  by 
drop  ammonium  sulphide  (which  should  be  more  or  less  yellow 
and  contain  no  free  ammonia),  not  fast  enough  to  check  the  boiling. 
Use  the  least  possible  excess  of  ammonium  sulphide.  Ascertain 
when  enough  has  been  added  by  stopping  the  boiling  long  enough 
for  the  nickel  sulphide  to  settle,  and  adding  a  drop  to  the  clear 
surface  of  the  solution.  If  more  is  required,  raise  the  heat  to 
boiling  before  adding  it.  When  further  addition  of  ammonium 
sulphide  produces  no  more  precipitate  boil  a  few  minutes  longer, 
and  add  enough  acetic  acid  to  give  a  decided  acid  reaction.  Add 
next  a  little  hydrogen  sulphide  solution  and  filter,  washing  with  a 
dilute  solution  of  hydrogen  sulphide.  Test  the  filtrate  by  neutral- 
izing with  ammonia  and  adding  one  or  two  drops  of  ammonium 

*  Journ.  Chem.  Soc.  16,  58. 


§110.]  NICKEL.  261 

sulphide.  If  this  causes  a  blackening  of  the  fluid,  boil  with 
addition  a  slight  excess  of  acetic  to  separate  the  nickel. 

fi.  Prepare  the  solution  as  above  described  (1,  6,  a).  Add 
sodium  or  ammonium  acetate,  if  acetates  are  not  already  present ; 
heat  to  boiling;  transmit  HaS  gas  through  the  boiling  solution 
about  ten  minutes.  The  precipitated  nickel  sulphide  settles 
readily.  Ascertain  whether  nickel  has  been  completely  separated 
by  adding  a  drop  of  ammonium  sulphide  to  the  clear  surface  of 
the  liquid.  If  no  blackening,  or  only  a  white  cloud  of  sulphur 
appears,  add  a  little  cold  strong  solution  of  hydrogen  sulphide 
in  water,  filter,  wash  the  precipitate  and  test  further  the  filtrate 
for  nickel  as  above  described.  If,  on  the  contrary,  the  drop  of 
ammonium  sulphide  causes  a  black  coloration  (nickel  sulphide)  an 
incomplete  separation  of  nickel  is  indicated,  which  may  be  due  to 
the  presence  of  too  much  free  acetic  acid.  Add,  therefore,  a  few 
drops  of  ammonia,  leaving  the  solution  however  still  slightly  acid, 
heat  again  to  boiling  and  pass  hydrogen  sulphide,  and  so  proceed 
till  complete  precipitation  is  effected.  It  should  be  borne  in  mind 
that  a  large  amount  of  free  acetic  prevents  precipitation  of  nickel 
as  sulphide,  while  a  small  amount  does  not.  The  slight  quantity 
of  acetic  present  throughout  the  operation  prevents  the  formation 
of  ammonium  sulphide  which  is  a  solvent  for  NiS,  and  also  pre- 
vents the  precipitation  of  the  alkali-earth  metals  if  they  are 
present.] 

Dry  the  washed  nickel  sulphide  in  the  funnel,  and  transfer 
from  the  filter  to  a  beaker ;  the  filter  is  incinerated  in  a  porcelain 
crucible  and  added  to  the  dry  precipitate.  The  precipitate  is  now 
treated  with  concentrated  nitrohydrochloric  acid,  and  the  mixture 
digested  at  a  gentle  heat,  until  the  whole  of  the  nickel  sulphide  is 
dissolved,  and  the  undissolved  sulphur  appears  of  a  pure  yellow ; 
the  fluid  is  then  diluted,  filtered,  and  the  filtrate  precipitated  as 
directed  in  1,  #,  and  the  nickel  oxide  thus  obtained  is  reduced  to 
metal  according  to  directions  in  2. 

c.  -By  direct  Ignition. 

The  same  method  as  described  §  109,  1,  e.     (Manganese.) 

2.  Determination  as  metallic  Nickel. 

Ignite  the  oxide  or  chloride  to  be  reduced  in  a  porcelain 
crucible  in  a  slow  stream  of  hydrogen,  at  first  gently,  then  more 
strongly  till  the  weight  is  constant.  For  properties  of  the  residue, 


262  DETERMINATION.  [§  111. 

see  §  79,  c.     If  on   dissolving  the  metal  in  nitric  acid  any  silica 
remains,  this  must  be  weighed  and  deducted. 

3.  Determination  as  Nickel  Sulphate. 

The  nickel  solution  should  be  free  from  other  non-volatile  salts. 
Evaporate  with  a  slight  excess  of  pure  sulphuric  acid  in  a  platinum 
dish  to  dryness  and  heat  for  15  or  20  minutes  moderately,  so  as 
just  to  drive  off  the  excess  of  sulphuric  acid  without  blackening 
the  yellow  sulphate  at  the  edges.  It  is  difficult  to  be  sure  of 
hitting  the  exact  point,  hence  we  cannot  place  dependence  on  this 
method  nor  on  that  of  GIBBS,  which  consists  in  dissolving  the 
sulphide  in  nitric  acid  and  evaporating  the  solution  with  sulphuric 
acid.  For  the  properties  of  the  residue,  see  §  79,  d. 

§m. 

4.  COBALT. 

a.  Solution. 

Cobalt  and  its  compounds  behave  with  solvents  like  the  corre- 
sponding compounds  of  nickel.  The  protosesquioxide  of  cobalt 
obtained  by  SCHWARZENBERG  in  microscopic  octahedra  does  not 
dissolve  in  boiling  hydrochloric  acid,  or  nitric  acid,  or  nitrohydro- 
chloric  acid  ;  but  it  dissolves  in  concentrated  sulphuric  acid,  and  in 
fusing  potassium  disulphate. 

b.  Determination. 

Cobalt  is  determined  in  the  metallic  state  or  as  sulphate,  being 
usually  first  precipitated  as  cobaltous  hydroxide,  sulphide  or  tripo- 
tassium  cobaltic  nitrate. 

We  may  convert  into 

1.  METALLIC  COBALT: 

a.  By  direct  reduction.  All  salts  of  cobalt,  which  can  be 
immediately  reduced  by  hydrogen  (chloride,  nitrate,  carbonate, 


b.  By  precipitation  as  cobaltous  hydroxide.     All  salts  soluble 
in  water  of  inorganic  acids,  and  insoluble  salts  of  such  acids  as  may 
be  removed  by  solution.     All  salts  of  volatile  organic  acids. 

c.  By  precipitation   as  sulphide.      All   compounds   of  cobalt 
without  exception. 

<L  By  presentation  as  tripotassium  cobaltic  nitrite.     All  com- 
pounds of  cobalt  soluble  in  water  or  dilute  acetic  acid. 


§  111.]  COBALT.  263 


*2.   COBALT  s 

a.  By  simple  evaporation  and  ignition.  —  The  oxygen    com- 
pounds of  cobalt  and  all  cobaltous  salts  of  acids  which  may  be 
completely   expelled  by  evaporation  and  ignition  with  sulphuric 
acid. 

b.  By  pwipitttt'um.    it  «    sulphide.  —  All    compounds  of   cobalt 
without  exception. 

The  method  1,  a,  is  preferable  to  all  others  when  it  can  be 
applied;  it  is  quick  and  gives  exact  results.  The  method  1,  i, 
gives  better  results  than  it  used  to  be  credited  with.  The  direct 
conversion  of  suitable  cobalt  compounds  into  sulphate  is  also  quite 
•satisfactory.  The  precipitations  as  sulphide  and  as  tripotassium 
•cobaltic  nitrate  are  rarely  used  except  in  separations. 

1.  Determination  a<s  metallic  Cobalt. 

a.  By  direct  reduction. 

Evaporate  the  solution  of  cobaltous  chloride,  or  nitrate  (which 
must  be  free  from  sulphuric  acid  and  alkali),  in  a  weighed  crucible, 
to  dryness,  cover  the  crucible  with  a  lid  having  a  small  aperture  in 
the  middle,  conduct  through  this  a  moderate  current  of  pure  dry 
hydrogen,  and  then  apply  a  gentle  heat,  which  is  to  be  increased 
gradually  to  intense  redness.  When  the  reduction  is  considered 
complete,  allow  to  cool  in  the  current  of  hydrogen,  and  weigh  ; 
ignite  again  in  the  same  way  and  repeat  the  process  until  the 
weight  remains  constant.  The  results  are  accurate.  For  the 
properties  of  cobalt,  see  §  80. 

As  regards  the  apparatus  to  be  employed,  see  §  108,  2. 

If.  By  precipitation  as  cobaltmis  hydroxide. 

The  best  material  for  the  precipitating  vessel  is  platinum, 
porcelain  may  also  be  used,  but  not  glass.  First  remove  any  large 
excess  of  acid  which  may  be  present  by  evaporation.  Heat  nearly 
to  boiling,  add  pure  potash  in  slight  excess,  and  continue  heating 
till  the  precipitate  is  brownish-black.  Pour  the  supernatant  fluid 
through  a  filter,  wash  the  precipitate  by  decantation  with  boiling 
water  repeatedly,  transfer  it  to  the  filter,  and  continue  the  washing 
with  boiling  water  till  the  washings  are  free  from  any  trace  of 
dissolved  substance.  Dry,  ignite  in  a  porcelain  crucible  (§  52)  till 
the  filter  is  thoroughly  burnt,  reduce  in  a  current  of  hydrogen, 
wash  the  metal  several  times  with  boiling  water,  dry,  ignite  again 
in  hydrogen  and  weigh.  Test  the  weighed  cobalt  by  dissolving  in 


264  DETERMINATION.  [§  111. 

nitric  acid.  If  any  silica  remains,  this  must  be  weighed  and 
deducted.  Mix  the  solution  with  ammonium  chloride  and  ammo- 
nium carbonate,  if  a  small  precipitate  (aluminium  or  ferric  hydrox- 
ide) forms,  ignite  and  weigh  this  too  and  deduct  it.  The 
results  are  excellent ;  the  amount  of  alkali  which  remains  with 
the  metal  when  the  work  is  done  properly  being  exceedingly 
minute.  Compare  §  80,  a. 

c.  By  precipitation  as  sulphide. 

Put  the  solution  in  a  flask,  add  ammonium  chloride,  then 
ammonia  just  in  excess,  then  ammonium  sulphide  as  long  as  a 
precipitate  is  produced,  nil  up  to  the  neck  with  water,  cork  and 
allow  to  stand  12  or  24  hours  in  a  warm  place.  Decant,  filter,  and 
wash  as  directed  §  109,  2.  Finally,  dry  and  proceed  as  directed 
§  110,  J,  /?,  to  redissolve  the  cobalt  sulphide.  Determine  the 
cobalt  according  to  5.  There  are  no  sources  of  error  in  the  pre- 
cipitation with  ammonium  sulphide.  For  the  properties  of  cobalt 
sulphide,  see  §  80.  It  cannot  be  brought  into  a  weighable  form 
by  ignition  in  hydrogen,  as  the  residue  is  a  variable  mixture  of 
different  sulphides  (H.  ROSE).  Cobalt  may  also  be  thrown  down 
as  sulphide  by  the  other  methods  given  under  Nickel.  The 
thorough  precipitation  of  cobalt  is  much  easier  than  that  of  nickel* 

d.  By  precipitation  as  tripotassium  cobaltic  nitrate. 

To  the  moderately  concentrated  solution  of  the  cobalt  salt  add 
potash  in  excess,  then  acetic  acid  till  the  precipitate  is  just  redis- 
solved,  then  a  concentrated  solution  of  potassium  nitrite  previously 
just  acidified  with  acetic  acid,  and  allow  to  stand  24  hours  at  a 
gentle  heat.  Filter,  wash  with  solution  of  potassium  acetate  (1  in 
10)  containing  some  potassium  nitrite,  till  all  foreign  substances  are 
removed,  dry,  dissolve  with  the  filter  ash  in  hydrochloric  acid, 
filter  and  determine  the  cobalt  according  to  1,  I.  This  method 
was  introduced  by  A.  STROMEYER  ;*  the  present  modification,  first 
suggested  by  H.  ROSE,  and  improved  by  FR.  G-AUHE,  is  the  surest 
to  yield  good  results  (GAUHEf).  For  the  properties  of  the  precipi- 
tate, see  §  80,  e. 

2.  Determination  as  sulphate, 
a.  By  direct  conversion. 

Add  to  the  solution  a  little  more  sulphuric  than  will  suffice  to 
form  cobaltous  sulphate  with  all  the  cobalt  present.     Evaporate, 
*  Annal.  d.  Chem.  u.  Pliarm.  90,  218.         f  Zeitschr.  f.  anal.  Chem.  4,  60. 


§  112.]  FKKKurs  IKON.  265 

using  a  platinum  dish  or  platinum  crucible,  at  all  events,  to  finish 
the  operation.  Heat  the  residue  cautiously  over  the  lamp,  gradu- 
ally increasing  the  temperature  to  dull  redness,  and  maintain  at 
this  point  for  15  minutes.  Should  the  edges  blacken,  moisten  with 
dilute  sulphuric  acid,  dry,  and  ignite  again  with  greater  caution. 
Properties  of  the  precipitate,  §  80.  Results  quite  satisfactory.* 

b.    With  previous  precipitation  as  sulphide. 

Precipitate  the  cobalt  as  sulphide  according  to  1,  c,  dissolve  it 
as  directed,  evaporate  with  excess  of  sulphuric  acid  in  a  porcelain 
dish  to  dryness,  take  up  the  residue  with  water,  transfer  the  solu- 
tion to  a  weighed  platinum  dish  and  proceed  according  to  2,  a. 

§  112- 

5.  FERROUS  IRON. 

a.  Solution. 

Many  ferrous  compounds  are  soluble  in  water.  Those  which 
are  insoluble  in  water  dissolve  almost  without  exception  in  hydro- 
chloric acid ;  the  solutions,  if  not  prepared  with  perfect  exclusion 
of  air,  and  with  solvents  absolutely  free  from  air,  contain  invariably 
more  or  less  ferric  chloride.  In  cases  where  it  is  wished  to  avoid 
the  chance  of  oxidation,  the  solution  of  the  ferrous  compound  is 
effected  in  a  small  flask,  through  which  a  slow  current  of  carbonic 
acid  gas  is  passed,  the  transmission  of  the  gas  being  continued 
until  the  solution  is  cold.  Many  native  ferrous  compounds  cannot 
be  thus  dissolved.  They  are,  indeed,  rendered  soluble  by  fusing 
with  sodium  carbonate,  but  in  this  process  ferric  oxide  is  formed. 
It  is  therefore  advisable  to  heat  such  substances  (in  the  finest  pow- 
der) with  a  mixture  of  3  parts  concentrated  sulphuric  acid  and  1 
part  water  in  a  strong  sealed  tube  of  Bohemian  glass  for  2  hours 
at  about  210°,  or — in  the  case  of  silicates — to  warm  them  with  a 
mixture  of  2  parts  hydrochloric  acid  and  1  part  strong  hydrofluoric 
acid  in  a  covered  platinum  dish  (A.  MrrscHERLicHf.  See  also 
Cooke's  method  of  solution,  §  160,  84).  Metallic  iron  dissolves  in 
hydrochloric  acid,  and  in  dilute  sulphuric  acid,  with  evolution  of 
hydrogen,  as  ferrous  chloride  or  sulphate  respectively;  in  warm 
nitric  acid  it  dissolves  as  ferric  nitrate,  and  in  nitrohydrochloric 
acid  as  ferric  chloride. 


*  Compare  GAUHE,  Zeitschr.  f.  anal.  Chem.  4,  55. 
f  Journ.  f.  prakt.  Cbem.  81,  116. 


266  J>KTKUM1NATION.  [§  112. 

b.  Determination. 

Ferrous  iron  may  be  estimated  1,  by  dissolving,  converting 
into  ferric  iron,  and  determining  the  latter  gravimetrically  or  volu- , 
metrically;  2,  by  precipitating  as  sulphide,  and  weighing  it  as 
such,  or  determining  it  after  conversion  into  a  ferric  salt ;  3,  by  a 
direct  volumetric  method. 

The  methods  1  and  2  are,  of  course,  only  applicable  when  no 
ferric  compound  is  present;  the  method  2  is  scarcely  ever  used 
except  for  separations.  The  methods  included  under  3  are  adapted 
to  most  cases,  and,  in  absence  of  other  reducing  substances,  are 
especially  worthy  of  recommendation. 

As  the  determination  of  iron  as  ferric  oxide  belongs  to  §  113, 
and  as  the  process  for  precipitating  ferrous  iron  as  sulphide  is  the 
same  as  that  for  precipitating  ferric  iron  in  this  form,  nothing 
remains  for  us  here  but  to  describe  the  methods  of  converting 
ferrous  into  ferric  salts  and  the  processes  included  under  3.  . 

1.  Methods  of  converting  Ferrous  into  Ferric  Iron. 

a.  Methods,  applicable  in  all  cases. 

Heat  the  solution  of  the  ferrous  salt  with  hydrochloric  acid  and 
add  small  portions  of  potassium  chlorate,  till  the  fluid,  even  after 
warming  for  some  time,  still  smells  strongly  of  chlorine.  Our 
object  may  be  also  attained  by  passing  chlorine  gas  or — in  the  case 
of  small  quantities — by  addition  of  chlorine  water,  or  very  con- 
veniently by  adding  solution  of  bromine  in  hydrochloric  acid.  If 
the  solution  is  required  to  be  free  from  excess  of  chlorine  or 
bromine,  it  is  finally  heated,  till  all  odor  of  chlorine  or  bromine 
has  disappeared. 

h.  Methods  which  are  only  suitable  when  the  iron  is  to  be  subse- 
quently precipitated  hy  ammonia*  as  ferric  hydroxide. 

Mix  the  solution  of  the  ferrous  salt  in  a  flask  with  a  little 
hydrochloric  acid,  if  it  does  not  already  contain  any ;  add  some 
nitric  acid,  and  heat  the  mixture  for  some  time  to  incipient  ebulli- 
tion. The  color  of  the  fluid  will  show  whether  the  nitric  acid  has 
been  added  in  sufficient  quantity.  Though  an  excess  of  nitric  acid 
does  no  harm,  still  it  is  better  to  avoid  adding  too  much  on  account 
of  the  subsequent  precipitation.  In  concentrated  solutions,  the 
addition  of  nitric  acid  produces  a  dark-brown  color,  which  disap- 
pears upon  heating.  This  color  is  owing  to  the  nitrogen  dioxide 


§  112.]  FEKKOUS    IIJOX.  267 

(N2O2)  formed  dissolving  in  the  portion  of  the  solution  which  still 
contains  ferrous  salt. 

c.  Methods  which  can  be  employed  only  when  the  ferric  iron  is 
to  be  determined  volumetrieally . 

Add  to  the  hydrochloric  solution  small  quantities  of  artificially 
prepared  iron-free  manganese  dioxide,  till  the  solution  is  of  a  dark 
olive-green  color  from  the  formation  of  manganic  chloride ;  boil 
till  this  coloration  and  the  odor  of  chlorine  have  disappeared  (Fit. 
MOHR)  ;  or  you  may  add  pure  potassium  permanganate  (in  crystals 
or  concentrated  solution)  till  the  fluid  is  just  red  and  then  boil,  till 
the  red  color  and  chlorine-odor  have  vanished.  These  methods 
present  the  advantage  of  permitting  complete  conversion  of  ferrous 
into  ferric  salts  without  the  use  of  any  considerable  excess  of  the 
oxidizing  agent. 

2.   Volumetric  Determination. 

a.  MARGUERITE'S  Method. 

If  we  add  to  a  solution  of  ferrous  salt,  containing  an  excess  of 
sulphuric  acid,  potassium  permanganate,  the  former  is  converted 
into  a  ferric  salt  by  the  oxidizing  action  of  the  latter  (10FeSO4  -|- 
8H2SO4  +  K,Mn268  =  5Fef(S04),  +  K,SO4  +  2MnSO4  +  8H2O). 
Now  if  we  possess  a  solution  of  potassium  permanganate,  and  know 
how  much  iron  100  c.c.  of  it  can  convert  from  the  ferrous  to  the  ferric 
condition,  we  can,  with  this,  readily  determine  an  unknown  quan- 
tity of  iron ;  we  have  simply,  for  this  purpose,  to  dissolve  the  iron 
in  acid,  in  the  form  of  a  ferrous  salt,  to  oxidize  the  solution  accu- 
rately, and  note  how  many  c.c.  of  the  solution  of  potassium  per- 
manganate have  been  used  to  accomplish  that  object. 

In  the  presence  of  hydrochloric  acid  (see  y),  the  change  is  not 
exactly  in  accordance  with  the  above  equation  (LOWENTHAL  and 
LENSSEN*). 

a.  Tit/ration  of  tlie  Solution  of  Potassium  Permangan- 
ate. 

Dissolve  5  grin,  (roughly  weighed)  of  pure  crystallized  potas- 
sium permanganate  in  distilled  water  by  the  aid  of  heat,  dilute  to  1 
litre,  and  preserve  in  a  stoppered  bottle.  Action  of  direct  sunlight 
on  the  solution  should  be  avoided.  The  solution,  if  carefully  kept, 
does  not  alter,  but  still  it  is  well  to  titrate  it  afresh  occasionally. 

*  Zeitschr.  f.  anal.  Chem.  1,  329. 


268  DETERMINATION.  [§  112. 

aa.  Titration  l>y  Metallic  Iron. 

Weigh  off  accurately  about  1  gnu.  thin  soft  iron  wire,  previ- 
ously cleaned  with  emery  paper,  transfer  to  a  J  litre  measuring 
flask,  containing  100  c.c.  dilute  sulphuric  acid  (1  to  5),  add  about  1 
rin.  sodium  bicarbonate,  to  produce  carbonic  acid  and  expel  the 
air,  and  then  close  the  flask  with  an  india-rubber  stopper,  provided 
with  an  evolution  tube,  as  shown  in  flg.  51  ;  <•  contains  20  or  30 

c.c.  water.  Heat  the  flask  at 
first  gently,  finally  to  gentle 
boiling  till  the  iron  is  dissolved. 
The  clip  l>  is  open,  and  the  hydro- 
gen escapes  through  the  water 
in  <:  Meanwhile  boil  about  300 
c.c.  distilled  water,  to  drive  out 
all  the  air  it  contains,  and  then 
allow  it  to  cool.  As  soon  as  the 
iron  is  entirely  dissolved,  remove 

the  lamp  and  close  the  evolution  tube  with  the  clip.  When  the 
iron  solution  has  cooled  a  little  loose  the  clip,  and  allow  the  water 
in  c  to  recede,  pour  the  boiled  water  into  c,  and  allow  this  also  to 
recede  till  the  solution  nearly  reaches  the  mark.  Take  out  the 
evolution  tube  and  close  the  flask  with  an  unperforated  stopper, 
allow  to  cool  to  the  temperature  of  the  room,  fill  with  water  to  the 
mark,  shake  and  allow  to  stand,  so  that  the  particles  of  carbon 
usually  present  may  deposit.  Now  take  out  with  a  pipette  50  c.c. 
of  the  clear  and  nearly  colorless  fluid  (containing  ^  of  the  iron 
weighed  off),  transfer  to  a  400  c.c.  beaker,  and  dilute  till  the  beaker 
is  half  full.  Place  the  beaker  on  a  sheet  of  white  paper,  or  better, 
on  a  sheet  of  glass,  with  white  paper  underneath. 

Fill  a  GAY-LUSSAC'S  or  GKJSSLEB'S  burette  of  30  c.c.  capacity, 
divided  into  -fa  c.c.  (see  p.  41,  figs.  13  and  14),  up  to  zero,  with  solu- 
tion of  potassium  permanganate,  of  which  take  care  to  have  ready 
a  sufficient  quantity,  perfectly  clear  and  uniformly  mixed. 

Now  add  the  permanganate  to  the  ferrous  solution,  starring  the 
latter  all  the  while  with  a  glass  rod.  At  first  the  red  drops  dis- 
appear very  rapidly,  then  more  slowly.  The  fluid,  which  at  first 
was  nearly  colorless,  gradually  acquires  a  yellowish  tint.  From 
the  instant  the  red  drops  begin  to  disappear  more  slowly,  add  the 
permanganate  with  more  caution  and  in  single  drops,  until  the  last 
drop  imparts  to  the  fluid  a  faint,  but  unmistakable  reddish  color, 


§  112.]  FERROUS   IRON.  269 

which  remains  on  stirring.  A  little  practice  will  enable  you  readily 
to  hit  the  right  point.  As  soon  as  the  fluid  in  the  burette  has 
sufficiently  collected  again  read  off,  and  mark  the  number  of  c.c. 
used.  The  reading  off  must  be  performed  with  the  greatest  exact- 
ness (see  §  22) ;  the  whole  error  should  not  amount  to  ^  c.c. 

The  amount  of  permanganate  solution  used  should  be  about 
20  c.c.  Repeat  the  experiment  with  another  50  c.c.  of  the  iron 
solution.  The  difference  between  the  permanganate  used  in  the 
two  cases  should  not  be  more  than  -1  c.c. ;  if  it  is,  make  one  more 
•experiment  and  when  the  results  are  sufficiently  near  take  the 
mean.  Now  calculate  what  quantity  of  iron  is  represented  by  100 
<-.e.  of  the  permanganate.  To  this  end  first  divide  the  iron 
weighed  off  by  5,  and  then  multiply  by  '996,  since  soft  iron  wire 
contains  on  the  average  *4  per  cent,  carbon,  &c. ;  this  gives  the 
quantity  of  pure  iron  contained  in  50  c.c.  of  the  solution.  Suppose 
we  took  1-050  grm.  iron  wire,  and  used  a  mean  of  21'3  c.c.  per- 
manganate, J-"°7r5-0-  =  '210,  -210  X  "996  =  -20910.  And  then  by 
rule  of  three  :— 

21-3  :  -20916::  100  :  x *  =  -98197; 

therefore,  100  c.c.  permanganate  =  -98197  pure  iron. 

If  there  is  a  deficiency  of  free  acid  in  the  solution  of  iron,  the 
fluid  acquires  a  brown  color,  turns  turbid,  and  deposits  a  brown 
precipitate  (manganese  dioxide  and  ferric  hydroxide).  The  same 
may  happen  also  if  the  solution  of  potassium  permanganate  is 
added  too  quickly,  or  if  the  proper  stirring  of  the  iron  solution  is 
omitted  or  interrupted.  Experiments  attended  with  abnormal 
manifestations  of  the  kind  had  always  better  be  rejected.  That 
the  fluid  reddened  by  the  last  drop  of  solution  of  potassium 
permanganate  added,  loses  its  color  again  after  a  time,  need  create 
no  surprise  or  uneasiness;  this  decolorization  is,  in  fact,  quite 
inevitable,  as  a  dilute  solution  of  free  permanganic  acid  cannot 
keep  long  undecomposed. 

55.  Titration  by  Ammonium  Ferrous  Sulphate. 

Weigh  off,  with  the  greatest  accuracy,  about  1-4  grin,  of  the 
pure  salt  prepared  according  to  the  directions  given  in  §  65,  4, 
•dissolve  in  about  200  c.c.  distilled  water,  previously  mixed  with 
about  20  c.c.  dilute  sulphuric  acid,  and  proceed  as  in  aa. 

By  dividing  the  amount  of  salt  weighed  off  by  7' 0014  (or  where 


270  DETERMINATION.  [§  112. 

great  accuracy  is  not  required  by  7)  we  obtain  the  quantity  of  iron 
corresponding. 

If  the  salt  is  not  pure,  if,  for  instance,  it  contains  basic  radicals 
isomorphous  with  ferrous  iron  (manganese,  magnesium,  &c.)  ;  or  if 
it  contains  ferric  iron,  or  is  moist,  the  result  will  of  course  be  too 
high. 

cc.  Titration  by  Oxalic  Acid. 

If  solution  of  potassium  permanganate  is  added  to  a  warm 
solution  of  oxalic  acid,  mixed  with  sulphuric  acid,  the  liberated 
permanganic  acid  oxidizes  the  oxalic  acid  to  carbon  dioxide  and 
water  [5H2C2O4  +  K2Mn2O8  +  3H2SO4  ^  K2S()4  +  2MnSO4  + 
10CO,  +  8H2O].  For  the  oxidation  of  1  mol.  oxalic  acid  (H2C2O4) 
and  2  at.  iron  (in  the  ferrous  state)  equal  quantities  of  permanganic 
acid  are  accordingly  required ;  therefore,  126  parts  (1  mol.)  of 
crystallized  oxalic  acid  correspond,  in  reference  to  the  oxidizing 
action  of  permanganic  acid,  to  112  parts  (2  at.)  of  iron. 

A  solution  of  oxalic  acid  is  altered  by  the  action  of  light ;  it  is, 
therefore,  well  only  to  dissolve  as  much  as  will  be  required  for 
immediate  use.  Dissolve  1  to  1*2  grm.  pure  acid  prepared  by 
§  65,  1,  to  250  c.c. ;  50  c.c.  of  this  solution  are  introduced  into 
a  beaker,  diluted  with  about  100  c.c.  water,  from  6  to  8  c.c.  cone, 
sulphuric  acid  added,  and  the  fluid  heated  to  about  60°.  The  beaker 
is  then  placed  on  a  sheet  of  white  paper,  and  permanganate  added 
from  the  burette,  with  stirring.  The  red  drops  do  not  disappear 
at  first  very  rapidly,  but  when  once  the  reaction  has  fairly  set  in, 
they  continue  for  some  time  to  vanish  instantaneously.  As  soon 
as  the  red  drops  begin  to  disappear  more  slowly,  the  solution  of 
potassium  permanganate  must  be  added  with  great  caution;  if 
proper  care  is  taken  in  this  respect,  it  is  easy  to  complete  the 
reaction  with  a  single  drop  of  permanganate ;  this  completion  of 
the  reaction  is  indicated  with  beautiful  distinctness  in  the  colorless 
fluid.  To  find  the  iron  corresponding  to  the  permanganate  used, 
multiply  the  amount  of  crystallized  oxalic  acid  in  the  50  c.c.  by  8 
and  divide  by  9. 

If  the  oxalic  acid  was  not  perfectly  dry,  or  not  quite  pure,  the 
result  of  the  experiment  will,  of  course,  lead  to  fixing  the  strength 
of  the  solution  of  potassium  permanganate  too  high.  Instead  of 
pure  oxalic  acid,  SAINT-GILLES  has  proposed  to  use  crystallized 
oxalate  of  ammonium  (NH4)2C2O4  +  HaO).  This  can  easily  be  pre- 
pared in  the  pure  state,"  keeps  well,  and  can  be  weighed  with 


§  112.]  FERROUS   IRON.  271 

accuracy.     142'08  parts  of  the  crystallized  salt  correspond  to  112 
parts  iron. 

Of  the  foregoing  three  methods  of  standardizing  solution  of 
potassium  permanganate,  the  first  is  the  one  originally  proposed  by 
MARGUERITE.  Ammonium  ferrous  sulphate  was  first  proposed  by 
FR.  MOHR,  and  oxalic  acid  by  HEMPEL,  as  agents  suitable  for  the 
purpose.  With  absolutely  pure  and  thoroughly  dry  reagents,  and 
proper  attention,  all  three  methods  give  correct  results. 

For  myself,  I  prefer  the  first  method,  as  the  most  direct  and 
positive,  the  only  doubtful  point  about  it  being  the  question 
whether  the  assumption  that  the  iron  wire  contains  99-6  per  cent, 
of  chemically  pure  iron  is  quite  correct ;  this,  however,  is  of  very 
trilling  importance,  as  the  error  could  not  exceed  y1^  or  y2^  per- 
cent.* The  other  two  methods  are,  as  may  readily  be  seen,  some- 
what more  convenient,  but  they  are  not  so  trustworthy  unless  you 
can  insure  the  purity  and  dryness  of  the  preparations. 

For  the  analysis  of  very  dilute  solutions  of  iron,  e.g.,  chalybeate 
water,  in  which  the  amount  of  iron  may  be  very  approximately 
determined  with  great  expedition,  by  direct  oxidization  with  per- 
manganate, a  very  dilute  standard  solution  must  be  prepared. 
Such  a  solution  may  be  made  by  diluting  the  previous  solution 
with  9  parts  of  water  or  by  dissolving  -5  grin  crystals  of  potassium 
permanganate  in  1  litre  of  water.  It  is  to  be  directly  standardized 
with  correspondingly  small  quantities  of  iron,  ferrous  salt,  or  oxalic 
acid. 

In  experiments  of  this  kind,  the  fact  that  a  certain  quantity  of 
permanganate  is  required  to  impart  a  distinct  color  to  pure  acidi- 
fied water  (which  is  of  no  consequence  in  operations  where  the 
concentrated  solution  is  used)  must  be  taken  into  consideration  ;  for 
where  the  solution  used  is  so  highly  dilute,  it  takes  indeed  a  measur- 
able quantity  of  it  to  impart  the  desired  reddish  tint  to  the  amount 
of  water  employed.  In  such  cases,  the  volume  of  the  solution  of 
iron  used  for  standardizing  the  permanganate  and  the  volume  of 
the  wreak  ferruginous  solution  subjected  to  analysis  should  be  the 
same,  and  either  the  two  solutions  should  contain  about  the  same 
quantity  of  iron,  or  by  means  of  a  special  experiment,  it  is  ascer- 
tained how  many  y1^  c.c.  of  the  permanganate  are  required  to 

*  If  you  are  ofton  making  iron  determinations,  you  may  of  course  procure  a 
quantity  of  wire  and  determine  the  amount  of  the  foreign  matter  in  it. 


272 


DETERMINATION. 


[ 


impart  the  desired  pale  red  color  to  the  same  volume  of  acidified 
water.  In  the  latter  case,  these  ^  c.c.  will  be  deducted  from  the 
amount  of  permanganate  used  in  the  regular  experiments. 


Fig.  52. 

ft.  Performance  of  the  Analytical  Process. 
This  has  been  fully  indicated  in  a.  The  compound  to  be 
examined  is  dissolved,  preferably  with  application  of  a  current  of 
carbon  dioxide*  (see  fig.  52).  in  dilute  sulphuric  acid,  allowed  to 
cool  in  the  current  of  carbon  dioxide,  and  suitably  diluted  (if  prac- 
ticable, the  solution  of  a  substance  containing  about  '2  grm.  iron 
should  be  diluted  to  about  200  c.c.) ;  if  free  acid  is  not  present  in 
sufficient  quantity,  dilute  sulphuric  acid  is  added  till  about  20  c.  c. 
are  present  altogether,  and  then  standard  permanganate  from  the 
burette,  to  incipient  reddening  of  the  fluid.  The  volume  of  stand- 
ard solution  used  is  then  read  off.  The  strength  of  the  solution  of 
permanganate  being  known,  the  quantity  of  iron  present  in  the 
examined  fluid  is  found  by  a  very  simple  calculation.  Suppose 
100  c.  c.  of  solution  of  potassium  permanganate  to  correspond  to 
•98  grm.  iron,  and  25  c.c.  of  the  solution  to  have  been  used  to 
effect  the  oxidation  of  the  ferrous  compound  examined,  then 

100  :  25:: -98  :  a?;  x  =  '245. 


*  If  commercial  hydrochloric  acid  is  used  for  the  preparation  of  CO2  by  action 
on  marble,  it  must  be  free  from  sulphurous  acid — an  impurity  which  it  often 
contains. 


§  112.]  FEKKOUS   IKON.  273 

The  quantity  of  ferrous  iron  originally  present  amounted 
accordingly  to  '245  grm. 

For  the  method  of  determining  the  total  amount  of  iron 
present  in  a  solution  containing  both  ferrous  and  ferric  salts,  I 
refer  to  §  113 ;  for  that  of  determining  the  amount  in  each  con- 
dition separately,  to  Section  Y. 

y.  Process  to  be  used  with  hydrochloric  solutions  of  Iron. 

In  titrating  hydrochloric  acid  solutions  of  iron  with  perman- 
ganate, it  is  essential  that  the  standardizing  of  the  reagent  and  the 
actual  analysis  be  performed  under  the  same  circumstances  as 
regards  dilution,  amount  of  acird,  and  temperature.  Besides  the 
proper  reaction  lOFeCI,  +  K,Mn,O8  +  16HC1  =  5Fe2Cl6  +  2KC1 
+  2MnCl,  +  8H,O,  the  collateral  reaction  KaMn3O8  +  16HC1  = 
2KC1  -f-  2MnCla  -f-  8H3O  -f-  10C1  also  takes  place,  in  consequence 
•of  which  a  little  chlorine  is  liberated.  This  chlorine  does  not 
combine  with  the  ferrous  chloride  to  form  ferric  chloride  in  the 
case  of  considerable  dilution,  but  there  occurs  a  condition  of 
equilibrium  in  the  fluid  containing  ferrous  chloride,  chlorine,  and 
hydrochloric  acid,  which  is  destroyed  by  addition  of  a  further 
quantity  of  either  body  (LOWENTHAL  and  LENSSEN*).  But  since 
it  is  difficult  to  observe  the  above  conditions  of  obtaining  correct 
results,  the  determination  in  presence  of  hydrochloric  acid  is 
always  less  trustworthy  than  it  is  in  sulphuric  acid  solutions. 

The  following  method  I  have,  however,  found  f  to  give  the 
best  results : — 

Standardize  the  permanganate  by  means  of  iron  dissolved  in 
dilute  sulphuric  acid,  make  the  iron  solution  to  be  tested  up  to  J 
litre,  add  50  c.c.  to  a  large  quantity  of  water  acidified  with  sul- 
phuric acid  (about  1  litre),  titrate  with  permanganate,  then  again  add 
50  c.c.  of  the  iron  solution,  and  titrate  again,  &c.  &c.  The  num- 
bers obtained  at  the  third  and  fourth  time  are  taken.  These  are 
constant,  while  the  number  obtained  the  first  time,  and  sometimes 
also  the  second  time,  differs.  The  result  multiplied  by  5  gives 
exactly  the  quantity  of  permanganate  proportional  to  the  amount 
of  ferrous  iron  present. 

J.  PENNY'S  Method  (recommended  subsequently  by  SCHABUS). 

If  potassium  dichromate  is  added  to  a  solution  of  a  ferrous  salt 
in  presence  of  a  strong  free  acid,  the  ferrous  salt  is  converted  into 

*  Zeitschr.  f.  anal.  Chem.  1.  329.  \  Ib.  1,  361. 


274  DETERMINATION.  [§  112.. 

ferric  salt,  whilst  a  potassium,  and  a  chromic  salt  of  the  free  acid  is 
formed  (6FeSO4  +  K3Cr2O7  +  7H2SO4=3Fe2(SO4)3  +  K,SO4  +  Or,. 
(SOO.+7H.O). 

Now,  witli  29*522  gr.  potassium  dichromate  dissolved  to  2  litres 
of  fluid,  33'6  gr.  iron  may  be  changed  from  a  ferrous  to  a  ferric 
salt,  (295-22  being  the  mol.  weight  of  KaO2O7,  and  336  being  6 
times  the  at.  weight  of  iron ;)  50  c.c.  of  the  above  solution  corre- 
spond accordingly  to  '84  grin.  iron. 

Care  must  be  taken  to  use  perfectly  pure  potassium  dichromate ; 
the  salt  is  heated  in  a  porcelain  crucible  until  it  is  just  fused ;  it  is 
then  allowed  to  cool  under  the  desiccator,  and  the  required  quan- 
tity weighed  off  when  cold.  Besides  the  above  solution,  another 
should  also  be  prepared,  ten  times  more  dilute. 

It  is  always  advisable  to  test  the  correctness  of  the  standard 
solution  of  potassium  dichromate,  by  oxidizing  with  it  a  known 
amount  of  pure  iron  dissolved  to  a  ferrous  salt  (see  p.  268,  aa). 

The  ferrous  solution  is  sufficiently  diluted,  mixed  with  a  suf- 
ficient quantity  of  dilute  sulphuric  acid,  and  the  standard  solution 
of  potassium  dichromate  slowly  added  from  the  burette,  the  liquid 
being  stirred  all  the  while  with  a  thin  glass  rod.  The  fluid,  which 
is  at  first  nearly  colorless,  speedily  acquires  a  pale  green  tint,  which 
changes  gradually  to  a  darker  chrome-green.  A  very  small  drop 
of  the  mixture  is  now  from  time  to  time  taken  out  by  means  of 
the  stirring-rod,  and  brought  into  contact  with  a  drop  of  a  solution 
of  potassium  ferricyanide  (free  from  f errocyanide)  on  a  porcelain 
plate,  which  has  been  spotted  with  several  of  such  drops.  When 
the  blue  color  thereby  produced  begins  to  lose  the  intensity  which 
it  exhibited  on  the  first  trials,  and  to  assume  a  paler  tint,  the 
addition  of  the  solution  of  potassium  dichromate  must  be  more 
carefully  regulated  than  at  first,  and  towards  the  end  of  the  process, 
a  fresh  essay  must  be  made,  and  with  larger  drops  than  at  first, 
after  each  new  addition  of  two  drops,  and  finally,  even  of  a  single 
drop ;  drops  must  also  be  left  for  some  time  in  contact  before  the 
observation  is  taken.  When  no  further  blue  coloration  ensues,  the 
oxidation  is  terminated.  From  the  remarkable  sensitiveness  of  the 
reaction,  the  exact  point  may  be  easily  hit  to  a  drop.  To  heighten 
the  accuracy  of  the  results,  the  dilute  (ten  times  weaker)  standard 
fluid  should,  just  at  the  end  of  the  process,  be  substituted  for  the 
concentrated  solution  of  potassium  dichromate. 

For   the  manner   of    proceeding   in   presence  of  ferric   salts. 


§  113.  j  FERRIC   IRON.  275 

1  refer  to  §  113.  If  there  is-  a  deficiency  of  free  acid  in  the 
solution,  brown  chromic  chromate  may  form,  upon  which  the 
solution  of  ferrous  salt  exercises  no  longer  a  deoxidizing  action. 

This  method  is  usually  preferred  to  the  preceding  when  hydro- 
chloric acid  is.  unavoidably  present. 

§113. 

6.  FERRIC  IRON. 

a.  Solution. 

Many  ferric  compounds  are  soluble  in  water.  Ferric  oxide  and 
most  ferric  compounds  which  are  insoluble  in  water,  dissolve  in 
hydrochloric  acid,  but  many  of  them  only  slowly  and  with  diffi- 
culty ;  compounds  of  this  nature  are  best  dissolved  in  concentrated 
hydrochloric  acid,  in  a  flask,  with  the  aid  of  heat ;  which,  however, 
should  not  be  allowed  to  reach  the  boiling-point ;  the  compound 
must,  moreover,  be  finely  powdered,  and  even  then  it  will  often 
take  many  hours  to  effect  complete  solution.  Fusion  with  sodium 
carbonate  or  potassium  disulphate  must  sometimes  be  resorted  to 
in  case  of  native  ferric  compounds. 
/  b.  Determination. 

The  iron  of  ferric  compounds  is  usually  weighed  as  ferric 
oxide,  but  sometimes  as  ferrous  sulphide  (§  81).  It  may,  however, 
be  estimated  also  indirectly,  and  also  by  volumetric  analysis,  both 
directly  and  after  reduction  to  ferrous  iron.  The  conversion  of 
compounds  of  iron  into  ferric  oxide  is  effected  either  by  precipita- 
tion as  ferric  hydroxide,  preceded  in  some  cases  by  precipitation  as 
ferrous  sulphide,  or  as  basic  ferric  acetate,  succinate,  or  formate ; 
or  by  ignition.  While  the  volumetric  and  the  now  seldom-used 
indirect  methods  are  applicable  in  almost  all  cases,  we  may  convert 
into 

1.  FERRIC  OXIDE. 

a.  By  Precipitation  as  Ferric  Hydroxide. 

All  salts  soluble  in  water  of  inorganic  or  volatile  organic  acids, 
and  likewise  those  which,  insoluble  in  water,  dissolve  in  hydro- 
chloric acid,  with  separation  of  their  acid. 

5.  By  Precipitation  as  Ferrous  Sulphide. 

All  compounds 'of  iron  without  exception. 

c.  By  ignition. 

All  ferric  salts  of  volatile  oxygen  acids. 


276  DETERMINATION.  [§  113. 

2.  FERROUS  SULPHIDE. 

All  compounds  of  iron  without  exception. 

The  method  1,  c,  is  the  most  expeditious  and  accurate,  and  is 
therefore  preferred  in  all  cases  where  its  application  is  admissible. 
The  method  1,  #,  is  the  most  generally  used.  The  •methods  1,  &, 
and  2,  serve  principally  to  effect  the  separation  of  the  iron  from 
other  bases ;  they  are  resorted  to  also  in  certain  instances  where  a 
is  inapplicable,  especially  in  cases  where  sugar  or  other  non-volatile 
organic  substances  are  present ;  and  also  to  determine  iron  in  ferric 
phosphates  and  borates.  For  the  manner  of  determining  iron  in 
ferric  chromate  and  silicate,  I  refer  to  §§  130  and  140.  The  volu- 
metric methods  for  estimating  the  iron  of  ferric  compounds  are 
used  in  technical  work  almost  to  the  exclusion  of  all  others,  and 
are  very  frequently  employed  in  scientific  analyses. 

1.  Determination  as  Ferric  Oxide. 

a.  By  Precipitation  as  Ferric  Hydroxide. 

Mix  the  solution  in  a  dish  or  beaker  with  ammonia  in  excess, 
heat  nearly  to  boiling,  decant  repeatedly  on  to  a  filter,  wash  the 
precipitate  carefully  with  hot  water,  dry  thoroughly  (which  very 
greatly  reduces  the  bulk  of  the  precipitate),  and  ignite  in  the 
manner  directed  in  §  53. 

For  the  properties  of  the  precipitate  and  residue,  see  §  81.  The 
method  is  free  from  sources  of  error.  The  precipitate,  under  all 
circumstances,  even  if  there  are  no  fixed  bodies  to  be  washed  out, 
must  be  most  carefully  and  thoroughly  washed,  since,  should  it 
retain  any  traces  of  ammonium  chloride,  a  portion  of  the  iron 
would  volatilize  in  the  form  qf  ferric  chloride.  It  is  also  highly 
advisable  to  dissolve  the  weighed  residue,  or  a  portion  of  it,  in 
strong  hydrochloric  acid,  to  see  whether  it  is  quite  free  from  silicic 
acid.  The  solution  is  most  readily  effected  in  hydrochloric  acid 
if  the  oxide  is  previously  -reduced  to  metallic  iron  by  ignition  in 
hydrogen. 

1).  By  Precipitatioii  as  Ferrous  Sulphide. 

The  solution,  in  a  not  too  large  flask,  is  mixed  with  ammonia, 
till  all  the  free  acid  is  neutralized.  (In  the  absence  of  organic, 
non- volatile  substances,  this  leads  to  the  precipitation  of  a  little 
ferric  hydroxide,  which,  however,  is  of  no  consequence.)  Add 
ammonium  chloride,  if  not  already  present  in  sufficient  quantity, 
then  colorless  or  yellowish  ammonium  sulphide  in  moderate  excess, 


§  113.]  FERRIC    IRON.  277 

lastly  water,  till  the  fluid  reaches  to  the  neck  of  the  flask.  Cork 
it  up  and  stand  in  a  warm  place  till  the  precipitate  has  subsided, 
and  the  supernatant  fluid  has  a  clear  yellowish  appearance  (without 
a  tinge  of  green).  Wash  as  directed  in  the  case  of  manganese 
sulphide  (§  109,  1,  <?).  Xeglect  of  any  of  these  precautions  will 
occasion  some  loss  of  substance,  the  ferrous  sulphide  gradually 
combining  with  the  oxygen  of  the  air,  and  passing  thus  into  the 
filtrate  as  ferrous  sulphate.  As  this  sulphate  is  reprecipitated  by 
the  ammonium  sulphide  present,  the  filtrate  assumes,  in  such  cases, 
a  greenish  color,  and  gradually  deposits  a  black  precipitate,  the 
separation  of  which  is  highly  promoted  by  addition  of  ammonium 
chloride.  [See  remarks  in  [  ]  §  81,  5,  c.  p.  165.] 

When  the  operation  of  washing  is  completed,  the  moist  pre- 
cipitate (if  it  is  not  dried  and  determined  according  to  2)  is  put, 
together  with  the  filter,  into  a  beaker,  some  water  added,  and  then 
hydrochloric  acid,  until  the  whole  is  redissolved.  Heat  is  now 
applied,  until  the  solution  smells  no  longer  of  hydrogen  sulphide ; 
the  fluid  is  then  filtered  into  a  flask,  the  residual  paper  carefully 
washed,  incinerated,  the  ash  treated  with  warm  strong  hydrochloric 
acid.  The  solution  thus  obtained  (if  yellowish)  is  added  to  the 
main  filtrate,  which  is  next  heated  with  nitric  acid  (see  §  112,  1) ; 
the  solution  (now  ferric)  is  finally  precipitated  with  ammonia,  as 
in  a. 

If  a  solution  of  potassium  ferric,  ammonium  ferric,  or  sodium 
ferric  tartrate  contains  a  considerable  excess  of  alkali  carbonate, 
the  precipitation  of  the  iron  as  sulphide  is  prevented  to  a  greater 
or  less  extent  (BLUMENAU).  In  such  cases  the  fluid  must  therefore 
be  nearly  neutralized  with  an  acid,  before  the  precipitation  with 
the  ammonium  sulphide  can  be  effected. 

C.    By  Ljitttnnt. 

Expose  the  compound,  in  a  covered  crucible,  to  a  gentle  heat 
at  first,  and  gradually  to  the  highest  degree  of  intensity ;  continue 
the  operation  until  the  weight  of  the  residuary  ferric  oxide  remains 
constant. 

2.  Determination  as  Anhydrous  Ferrous  Sulphide. 
The  hydrated  ferrous  sulphide  obtained,  as  in  1,  J,  may  be  very 
conveniently  determined   by  conversion  into  the  anhydrous  sul- 
phide.    The  process  is  the  same  as  for  zinc  (§  108,  2).     The  heat  • 
to  which  it  is  finally  exposed  in  the  current  of  hydrogen  must  be 


278  DETERMINATION.  [§  113. 

strong,  as  an  excess  of  sulphur  is  retained  with  some  obstinacy.  In 
fact,  it  is  advisable  after  weighing  to  re-ignite  in  hydrogen  and 
weigh  a  second  time.  It  is  of  no  importance  if  the  hydrated  sul- 
phide has  oxidized  on  drying. 

Ferrous  sulphate  and  ferric, hydroxide  can  be  transformed  into 
sulphide  in  the  same  manner,  after  having  been  dehydrated  by 
ignition  in  a  porcelain  crucible  (H.  ROSE*). 

The  results  obtained  by  OESTEN,  and  adduced  by  ROSE,  as  well 
as  those  obtained  in  my  own  laboratory,  are  exceedingly  satisfac- 
tory. (Expt.  No.  75.) 

3.  Volumetric  Determination. 

a.  Preceded  by  deduction  of  Ferric  to  Ferrous  Iron. 

"We  have  to  occupy  ourselves  simply  with  the  reduction  of  fer- 
ric to  ferrous  solutions,  the  other  part  of  the  process  having  been 
fully  discussed  in  §  112  (Ferrous  Iron).  This  reduction  can  be 
effected  by  many  substances  (zinc,  stannous  chloride,  hydrogen 
sulphide,  sulphurous  acid,  &c.),  but  only  those  can  be  used  with 
advantage,  an  excess  of  which  may  be  added  with  impunity.  If 
an  excess  must  be  very  carefully  avoided,  or,  being  added,  must  be 
carefully  removed,  the  method  becomes  troublesome,  and  a  ready 
source  of  inaccuracy  is  introduced. 

Reduction  by  Zinc. — Heat  the  hydrochloric  or  sulphuric  acid 
solution,  which  must  contain  a  moderate  excess  of  acid,  but  be  free 
from  nitric  acid,  in  a  small  long-necked  flask,  placed  in  a  slanting 
position ;  drop  in  small  pieces  of  iron-free  zinc  (§  60),  and  conduct 
a  slow  current  of  carbon  dioxide  through  the  flask  (fig.  52,  p.  272). 
Evolution  of  hydrogen  gas  begins  at  once,  and  the  color  of  the 
solution  becomes  paler  in  proportion  as  the  ferric  sulphate  (or 
chloride)  changes  to  ferrous  sulphate  (or  chloride).  Apply  a  mode- 
rate heat,  to  promote  the  action ;  and  add  also,  if  necessary,  a  little 
more  zinc.  As  soon  as  the  hot  solution  is  completely  decolorized 
(one  cannot  judge  of  the  perfect  reduction  of  a  cold  solution  so 
well,  as  the  color  of  a  ferric  salt  is  deeper  when  hot),  allow  to  cool 
completely  in  the  stream  of  carbon  dioxiode ;  to  hasten  the  cooling 
the  flask  may  be  immersed  in  cold  water ;  then  dilute  the  contents 
with  water,  pour  off  and  wash  carefully  into  a  beaker,  leaving 
behind  any  undissolved  zinc,  and  also  (as  far  as  possible)  any  flocks 
of  lead  that  may  have  separated  from  the  zinc,  and  proceed  as 

*Pogg.  Annal.  110,  1?6. 


§113.]  FERRIC    IKON.  279 

directed  in  §  112,  2.  If  the  solution  contain  metals  precipitable 
by  zinc,  these  will  separate,  and  may  render  filtration '  necessary. 
In  this  case  the  filtrate  must  be  again  heated  with  zinc  before  using 
the  standard  solution.  If  iron-free  zinc  cannot  be  procured,  the 
percentage  of  iron  in  the  metal  used  must  be  determined,  and 
weighed  portions  of  it  employed  in  the  process  of  reduction ;  the 
known  amount  of  iron  contained  in  the  zinc  consumed  is  then  sul>- 
tracted  from  the  total  amount  of  iron  found. 

{Reduction  by  Hydrogen  Sulphide. — Pass  hydrogen  sulphide 
through  the  cold  ferric  solution  in  a  flask.  The  solution  should 
occupy  about  two-thirds  of  the  capacity  of  the  flask,  and  should 
not  contain  much  more  than  *2  gr.  iron  per  100  c.c.,  but  may 
be  more  dilute  when  but  little  iron  is  present.  Continue 
the  treatment  with  hydrogen  sulphide  at  least  10  minutes 
after  the  color  due  to  the  ferric  salt  has  disappeared,  or  until  the 
solution  appears  to  be  well  saturated  with  that  gas.  Heat,  at  first 
cautiously,  to  boiling.  Escape  of  hydrogen  sulphide  at  this  period 
indicates  that  enough  of  that  reagent  has  been  applied.  Continue 
boiling  so  rapidly  that  air  cannot  enter  the  flask,  the  mouth  of 
which  may  be  partially  closed  by  a  loose  roll  of  filter  paper,  or  other 
means,  until  the  solution  is  reduced  to  one  half  its  first  volume. 
This  will  insure  the  removal  of  excess  of  hydrogen  sulphide.  (The 
escaping  vapor  will  cease  to  blacken  paper  dipped  in  an  alkaline 
lead  solution  somewhat  before  this  point  is  reached.)  During  the 
boiling,  let  the  flask  be  inclined  so  as  to  prevent  mechanical  loss. 
When  the  boiling  is  discontinued  fill  the  flask  immediately  with 
€old  water  to  within  an  inch  of  the  mouth,  close  with  a  stopper, 
and  cool  in  a  stream  of  water. 

Before  reducing  the  ferric  solution  by  either  of  the  above  pro- 
cesses, it  is  desirable  to  remove  hydrochloric  acid,  if  it  is  present, 
so  that  the  iron  after  reduction  can  be  satisfactorily  determined  by 
means  of  potassium  permanganate. 

Chlorides  can  be  decomposed  and  hydrochloric  acid  removed 
by  evaporating  the  solution  with  excess  of  sulphuric  acid  so  long 
as  hydrochloric  acid  vapors  are  given  off  at  a  temperature  slightly 
exceeding  100°  C.  A  liberal  excess  of  sulphuric  acid  is  advan;iv- 
geous.  After  cooling  add  water  and  digest  till  the  ferric  sulphate 
is  dissolved.  This  treatment  is  simple  and  safe  when  nothing  is 
present  which  is  thereby  converted  into  a  compound  insoluble  in 
dilute  sulphuric  acid  (silicic  acid,  barium,  strontium,  much  cal- 


280  DETERMINATION.  [§  llo. 

cium,  <fec.).  Such  insoluble  compounds  may  persistently  retain 
iron. 

When,  therefore,  by  evaporation  with  sulphuric  acid  and  sub- 
sequent treatment  with  water  an  insoluble  residue  remains,  it 
should  not  be  thrown  away  before  testing  it  to  ascertain  whether 
it  retains  iron.] 

b.  Without  previous  Reduction  to  Ferrous  Iron,  after  OUDE- 
MANS.'* 

If  an  acid  solution  of  ferric  chloride  is  mixed  with  a  little  cupric 
sulphate  and  some  potassium  sulphocyanate  and  then  sodium  thio- 
sulphate  is  added,  the  red  color  of  the  ferric  sulphocyanate  gets 
paler  and  paler,  and  finally  when  the  ferric  salts  are  reduced  to  fer- 
rous, disappears  altogether.  Warming  is  unnecessary.  To  hit  the 
point  is  not  easy,  so  we  add  a  slight  excess  of  sodium  thiosulphate, 
and  then  titrate  back  with  standard  iodine.  The  reaction  is  as  fol- 
lows :  Fe2Cl6  +  2Na2S2O3  =  2FeCl2  +  2NaCl  +  Na^S4Oa ;  it  is  pro- 
moted by  the  addition  of  a  small  quantity  of  cupric  sulphate,  which 
is  alternately  reduced  by  the  thiosulphate  and  oxidized  by  the  fer- 
ric chloride.  If  a  small  quantity  of  cuprous  salt  is  produced  by 
the  excess  of  thiosulphate  this  does  not  matter,  as  its  action  on  the 
iodine  solution  is  the  same  in  extent  as  the  action  of  the  thiosul- 
phate which  produced  it.  The  method  is  not  accurate  unless  the 
fluid  remains  clear ;  neither  cuprous  sulphocyanate  nor  cuprous 
iodide  nor  sulphur  must  be  thrown  down.  Hence  care  must  be 
taken  to  maintain  the  proper  amounts  of  the  reagents  and  to  dilute 
the  fluid  sufficiently. 

We  require — 1.  A  solution  of  sodium  thiosulphate  containing 
about  24  gr.  (of  the  crystallized  salt)  per  litre.  2.  A  solution  of 
ferric  chloride  of  known  strength,  prepared  by  dissolving  10*04: 
grm.  of  clean,  fine,  and  soft  iron  wire  (=10  grm.  pure  iron),  in 
hydrochloric  acid  in  a  slanting  long-necked  flask,  oxidizing  the  solu- 
tion with  potassium  chlorate,  completely  removing  the  excess  of 
chlorine  by  protracted  gentle  boiling,  and  finally  diluting  the  solu- 


*  Sodium  thiosulphate  wa's  first  employed  by  SCHERER  (Gel.  Anz.  der  K. 
Bayerischen  Akademie,  vom  31  Aug.  1859),  afterwards  by  KREMER  and  LAN- 
DOLT  (Zeitschr.  f.  anal.  Chem.  1,  214).  The  method  of  OUDEMANS  is  to  be  found 
in  Zeitschr.  f.  anal.  Chem.  6, 129;  it  was  criticised  and  rejected  in  MoHRlsLehrb. 
d.  Titrirmethode,  3  Anfl.  291.  OUDEMANS  replied  to  MoHRin  Zeitschr.  f.  anal. 
Chem.  9,  342,  and  an  examination  of  the  method  by  C.  BALLING,  appeared  in 
the  same  journal,  9,  99. 


jj  114.]  URAMl.M    A.ND    UKAXYL.  281 

tion  to  1  litre.  3.  A  solution  of  cupric  sulphate,  1  in  100.  4.  A 
solution  of  potassium  sulphocyanate,  1  in  100.  5.  A  solution  of 
iodine  in  potassium  iodide,  containing  5  or  6  grm.  iodine  in  the 
litre  (compare  §  146,  a).  6.  Thin  starch  paste. 

Measure  off  some  of  the  sodium  thiosulphate,  add  starch  paste 
(§  146,  #),  and  then  titrate  with  iodine  solution,  in  order  to  deter- 
mine the  relation  between  the  two  solutions.  Now  transfer  10  or 
20  c.c.  of  the  ferric  chloride  to  a  beaker,  add  2  c.c.  concentrated 
hydrochloric  acid,  100  or  150  c.c.  water,  3  c.c.  copper  solution,  and 
1  c.c.  potassium  sulphocyanate,  titrate  with  sodium  thiosulphate 
till  the  fluid  just  loses  its  color,  add  at  once  some  starch  paste,  and 
titrate  back  with  iodine  solution  till  the  blue  color  appears.  Deduct 
the  thiosulphate  equivalent  to  the  iodine  solution  from  the  total 
quantity  of  thiosulphate  used,  and  the  remainder  will  represent  the 
amount  required  to  reduce  the  iron  present.  In  the  analysis  the 
conditions  should  be  similar  to  those  in  the  standardizing  of  the 
thiosulphate. 

This  method  is  very  rapid,  and  the  results,  though  not  so  accu- 
rate as  those  by  method  «,  are  quite  good  enough  for  many  tech- 
nical purposes. 

Supplement  to  the  Fourth  Group. 

§114. 
7.  URANIUM  AND  URANYL. 

If  the  compound  in  which  the  uranium  is  to  be  determined 
contains  no  other  fixed  substances,  it  may  often  be  converted  into 
uranous  uranate  U(UO4)2 — (called  also  uranoso-uranic  oxide  UO,- 
2UO3) — by  simple  ignition.  If  sulphuric  acid  is  present,  small  por- 
tions of  ammonium  carbonate  must  be  thrown  into  the  crucible 
towards  the  end  of  the  operation. 

In  cases  where  the  application  of  this  method  is  inadmissible, 
the  solution  of  uranium  (which,  if  it  contains  uranous  salts,  must 
first  be  wanned  with  nitric  acid,  until  they  are  converted  into  uranyl 
salts)  is  nearly  boiled  in  a  platinum  or  porcelain  dish,  and  pre- 
cipitated with  ammonia  in  slight  excess.  The  yellow  precipitate 
formed,  which  consists  of  hydrated  a/m/rrioni/wm  tt/><ti,<if<-.  is  filtered 
off  hot  and  washed  with  a  dilute  solution  of  ammonium  chloride,  to 
prevent  the  fluid  passing  milky  through  the  filter.  The  precipitate 
is  dried  and  ignited  (§  53).  To  make  quite  sure  of  obtaining  the 


282  DETERMINATION.  [§  114. 

uranous  uranate  in  tlie  pure  state,  the  crucible  is  ignited  for  some 
time  in  a  slanting  position  and  uncovered ;  the  lid  is  then  put  on, 
while  the  ignition  is  still  continuing ;  the  crucible  is  allowed  to 
cool  under  the  desiccator,  and  weighed  (HAMMELSBEKG). 

If  the  solution  from  which  the  uranyl  is  to  be  precipitated  con- 
tains other  basic  radicals  (alkali-earth  metals,  or  even  alkali  metals), 
portions  of  these  will  precipitate  along  with  the  ammonium  uranate. 
For  the  measures  to  be  resorted  to  in  such  cases,  I  refer  to  Sec- 
tion Y. 

The  reduction  of  the  uranous  uranate  to  the  state  of  uranous 
oxide  (UOa)  is  an  excellent  means  of  ascertaining  its  purity  for  the 
pin-pose  of  control.  This  reduction  should  never  be  omitted,  since 
PELIGOT  has  found  the  uranous  uranate  to  be  variable  in  composi- 
tion. It  is  effected  by  ignition  in  a  current  of  hydrogen  gas,  in  the 
way  described  §  111,  1  (Cobalt).  In  the  case  of  large  quantities 
the  ignition  must  be  several  times  repeated,  and  the  residue  must 
be  occasionally  stirred  with  a  platinum  wire.  While  cooling 
increase  the  current  of  gas  to  prevent  reabsorption  of  oxygen.  By 
intense  heating  the  property  of  spontaneous  ignition  in  the  air  is 
destroyed.  If  after  evaporating  a  solution  of  uranyl  chloride,  the 
residue  is  to  be  ignited  in  hydrogen,  heat  gently  at  first  in  the  gas 
to  avoid  loss  by  volatilization.  The  separation  of  uranyl  from 
phosphoric  acid  is  effected  by  fusing  the  compound  with  potassium 
cyanide  and  sodium  carbonate.  Upon  extracting  the  fused  mass 
with  water,  the  phosphoric  acid  is  obtained  in  solution,  whilst  ura- 
nium is  left  as  uranous  oxide.  KNOP  and  AKENDT*  have  employed 
this  method. 

Taking  237*6  as  the  atomic  weight  of  uranium,  U(UO4)2  ura- 
nous uranate  contains  84*77  per  cent,  of  uranium  and.  15*23  per 
cent,  of  oxygen.  UO2  uranous  oxide  contains  88*13  per  cent,  ura- 
nium and  11*87  per  cent,  of  oxygen. 

According  to  BELOHOUBECK,  f  uranium  may  be  also  determined 
volumetrically  by  reducing  the  solution  of  uranyl  acetate  or  sul- 
phate to  uranous  salts  with  zinc,  as  in  the  case  of  iron  (§  113,  3,  a). 
As  the  color  of  the  solution  is  no  safe  criterion  of  the  end  of  the 
reduction,  you  must  allow  the  action  of  the  zinc  to  continue  for  a 
considerable  time.  BELOHOUBECK  says,  a  quarter  of  an  hour  is 
sufficient  for  small  quantities,  half  an  hour  for  large  quantities. 


*  Chem.  Centralblatt,  1856,  773.  f  Zeitschr.  f.  anal.  Chem.  6,  120. 


§  11,").]  SILVER.  283 

The  solution  of  the  uranous  salt  is  diluted,  mixed  with  dilute  sul- 
phuric acid,  and  then  titrated  with  permanganate  to  incipient  red- 
dening. The  permanganate  is  standardized  by  §  112,  2,  1  at. 
uranium  =  2  at.  iron. 

BELOHOUBECK  obtained  good  results  also  in  hydrochloric  solu- 
tions, but  experiments  made  in  this  laboratory  have  shown  that 
these  are  liable  to  the  error  pointed  out  in  the  case  of  iron  (Comp. 
p.  273,  y),  at  least  in  the  presence  of  considerable  quantities  of 
hydrochloric  acid. 

Fifth  Group. 

SILVER LEAD MERCURY    IN    MERCUROUS    COMPOUNDS MERCURY    IN 

MERCURIC     COMPOUNDS COPPER BISMUTH CADMIUM (PALLA- 
DIUM). 

§115. 

1.  SILVER. 

a.  Solution. 

Metallic  silver,  and  those  of  its  compounds  which  are  insoluble 
in  water,  are  best  dissolved  in  nitric  acid  (if  soluble  in  that  acid). 
Dilute  nitric  acid  suffices  for  most  compounds ;  silver  sulphide, 
however,  requires  concentrated  acid.  The  solution  is  effected  best 
in  a  flask,  which  should  be  heated  if  necessary,  and  placed  in  a 
slanting  position  if  gas  is  evolved.  In  the  case  of  metallic  silver, 
or  silver  sulphide,  the  solution  is  heated  finally  to  gentle  boiling 
to  drive  off  nitrous  acid.  Silver  chloride,  bromide,  and  iodide  are 
insoluble  in  water  and  in  nitric  acid.  To  get  the  silver  contained 
in  chloride  and  bromide  in  solution,  proceed  as  follows : — Fuse  the 
salt  in  a  porcelain  crucible  (this  operation,  though  not  absolutely 
indispensable,  had  better  not  be  omitted),  pour  water  over  it,  put 
a  piece  of  clean  cadmium,  zinc,  or  iron  upon  it,  and  add  some 
dilute  sulphuric  acid.  Wash  the  reduced  spongy  silver,  first  with 
dilute  sulphuric  acid,  then  with  water,  and  finally  dissolve  it  in 
nitric  acid.  However,  as  we  shall  see  below,  the  quantitative 
analysis  of  these  salts  does  not  necessarily  involve  their  solution. 

b.  Determination. 

Silver  may  be  weighed  as  chloride,  sulphide,  or  cyanide,  or  in 
the  metallic  state  (§  82).  It  is  also  frequently  determined  by  volu- 
metric analysis. 


284  DETERMINATION.  [§  115. 

We  may  convert  into 

1.  SILVER  CHLORIDE  :  All  compounds  of  silver  without  excep- 
tion. 

2.  SILVER  SULPHIDE  :  3.  SILVER  CYANIDE  :  All  coin  pounds  solu- 
ble in  water  or  nitric  acid. 

4.  METALLIC  SILVER  :  Silver  oxide  and  some  silver  salts  of  readily 
volatile  acids;  silver  salts  of  organic  acids;  silver  chloride,  bro- 
mide, iodide,  sulphide,  and  sulphate. 

The  method  4  is  the  most  convenient,  especially  when  con- 
ducted in  the  dry  way,  and  is  preferred  to  the  others  in  all  cases 
where  its  application  is  admissible.  The  method  1  is  that  most 
generally  resorted  to.  2  and  3  serve  mostly  only  to  effect  the 
separation  of  silver  from  other  metals. 

In  assays  for  the  Mint,  silver  is  usually  determined  volumetric- 
ally  by  GAY-LUSSAC'S  method.  PISANI'S  volumetric  method  is 
especially  suited  to  the  determination  of  very  small  quantities  of 
silver.  H.  VOGEL'S  method  is  specially  useful  to  photographers.. 

1.  Determination  of  Silver  as  Chloride. 

a.  In  the  Wet  Way. 

Mix  the  moderately  dilute  solution  in  a  beaker  with  nitric  acid,, 
heat  to  about  70°,  and  add  hydrochloric  acid  with  constant  stirring 
till  it  ceases  to  produce  a  precipitate.  A  large  excess  of  hydro- 
chloric acid  must  be  avoided,  as  the  precipitate  is  not  absolutely 
insoluble  therein.  While  protecting  the  contents  of  the  beaker 
from  the  action  of  direct  sunlight  continue  the  heat  till  the  precipi- 
tate has  fully  settled,  pour  off  the  clear  fluid  through  a  small  filter^ 
rinse  the  precipitate  on  to  the  latter  by  means  of  hot  water  mixed 
with  some  nitric  acid,  wash  with  hot  water  containing  nitric  acidr 
then  with  pure  hot  water,  dry  thoroughly,  transfer  the  precipitate 
to  a  watch-glass  as  nearly  as  possible,  incinerate  the  filter  in  a 
weighed  porcelain  crucible,  treat  the  ash  (which  always  contains 
some  metallic  silver)  with  a  few  drops  of  nitric  acid  in  the  heat ; 
add  two  or  three  drops  of  hydrochloric  acid,  evaporate  cautiously 
to  dryness,  add  the  main  bulk  of  the  precipitate,  using  a  camel's- 
hair  brush  to  transfer  the  last  portions,  heat  cautiously  till  it  begins 
to  fuse  at  the  edge,  allow  to  cool,  and  weigh. 

To  remove  the  fused  mass  without  breaking  the  crucible,  lay 
a  small  piece  of  iron  or  zinc  upon  it,  and  then  add  very  dilute 
hydrochloric  or  sulphuric  acid.  The  chloride  will  be  reduced,  and 


§  115.]  SILVER.  285 

the  silver  may  now  be  detached  from  the  crucible  with  the  greatest 


For  the  properties  of  the  precipitate  see  §  82.  The  method 
gives  very  exact  results,  at  all  events  in  the  absence  of  any  con- 
siderable quantities  of  those  salts  in  which  silver  chloride  is  some- 
what soluble ;  compare  §  82.  To  avoid  error  in  this  respect,  it  is 
well  to  test  the  clear  filtrate  with  hydrogen  sulphide. 

1>.   In  the  Dry  Way. 

This  method  serves  more  exclusively  for  the  analysis  of  silver 
bromide  and  iodide,  although  it  can  be  applied  in  the  case  of  other 
compounds. 


Fig.  53. 

The  process  is  conducted  in  the  apparatus  illustrated  by  fig. 
53,  leaving  off  the  U  tube  e,  and  employing  a  straight  bulb- 
tube  or  a  plain  tube  with  porcelain  tray  instead  of  the  bent  tube  d. 

a  is  a  flask  for  disengaging  chlorine,  it  is  completely  filled  with 
pieces  of  pvrolusite  (native  manganese  dioxide)  of  the  size  of  hazel- 
nuts,  and  half  filled  with  strong  hydrochloric  acid.  The  chlorine 
is  conducted  to  the  bottom  of  c,  which  contains  a  layer  of  sulphuric 
acid  and  is  filled  above  with  pumice-stone  moistened  with  strong 
sulphuric  acid.  The  flow  of  chlorine  may  be  regulated  by  the 
stop-cock,  while  any  excess  accidentally  produced  is  conducted  by  a 
second  tube  to  the  bottom  of  the  cylinder  5,  in  which  it  is  absorbed 
by  a  soda  solution  ;  d  is  a  bulb-tube  intended  for  the  reception 


286  DETERMINATION.  [§  1L"). 

of  the  silver  iodide  or  bromide.  The  operation  is  commenced 
by  introducing  the  compound  to  be  analyzed  into  the  bulb,  and 
applying  heat  to  the  latter  until  its  contents  are  fused  ;  when  cold, 
the  tube  is  weighed  and  connected  with  the  apparatus.  Chlorine 
gas  is  then  evolved  from  a ;  when  the  evolution  of  the  gas  has 
proceeded  for  some  time,  the  contents  of  the  bulb  are  heated  to 
fusion,  and  kept  in  this  state  for  about  fifteen  minutes,  agitating 
now  and  then  the  fused  mass.  The  bulb-tube  is  then  removed 
from  the  apparatus,  allowed  to  cool,  and  held  in  a  slanting  position 
to  replace  the  chlorine  by  atmospheric  air;  it  is  subsequently 
weighed,  then  again  connected  with  the  apparatus,  and  the  former 
process  repeated,  keeping  the  contents  of  d  in  a  state  of  fusion  for 
a  few  minutes.  By  means  of  a  light  glass  tube  attached  by  a  piece 
of  rubber  tube  to  the  end  of  d  the  chlorine  escaping  during  the 
operation  may  be  conducted  into  the  open  air  or  into  a  flue.  The 
operation  may,  in  ordinary  cases,  be  considered  concluded  if  the 
weight  of  the  tube  suffers  no  variation  by  the  repetition  of  the 
process.  If  the  highest  degree  of  accuracy  is  to  be  attained,  heat 
the  silver  chloride  again  to  fusion,  passing  at  the  same  time  a  slow 
stream  of  pure,  dry  carbon  dioxide  through  the  tube,  in  order  to 
drive  out  the  traces  of  chlorine  absorbed  by  the  fused  chloride. 
Allow  to  cool,  hold  obliquely  for  a  short  time,  so  as  to  replace  the 
carbon  dioxide  by  air,  and  finally  weigh.  See  §  82. 

2.  Determination  as  Silver  Sulphide. 

Hydrogen  sulphide  precipitates  silver  completely  from  acid, 
neutral,  and  alkaline  solutions ;  ammonium  sulphide  precipitates  it 
from  neutral  and  alkaline  solutions.  The  precipitate  does  not 
settle  clearly  and  rapidly  except  a  free  acid  or  salt  be  present  (such 
as  nitric  acid  or  ah  alkali  nitrate).  Eecently  prepared  perfectly 
clear  solution  of  hydrogen  sulphide  may  be  employed  to  precipitate 
small  quantities  of  silver ;  to  precipitate  larger  quantities,  the  solu- 
tion of  the  salt  of  silver  (which  must  not  be  too  acid)  is  moderately 
diluted,  and  washed  hydrogen  sulphide  gas  conducted  into  it. 
After  complete  precipitation  has  been  effected,  and  the  silver  sul- 
phide has  perfectly  subsided  (with  exclusion  of  air),  it  is  collected 
on  a  weighed  filter,  washed,  dried  at  100°,  and  weighed.  For  the 
properties  of  the  precipitate,  see  §  82.  This  method,  if  properly 
executed,  gives  accurate  results.  The  operator  must  take  care  to 
filter  quickly,  and  to  prevent  the  access  of  air  as  much  as  possible 


§  115.]  SILVER.  287 

during  the  filtration,  since,  if  this  precaution  be  neglected,  sulphur 
is  likely  to  separate  from  the  hydrogen  sulphide  water,  which,  of 
course,  would  add  falsely  to  the  weight  of  the  silver  sulphide.  If 
the  presence  of  a  minute  quantity  of  sulphur  in  the  precipitate  is 
suspected,  treat  it  after  drying  with  pure  carbon  disulphide  on  the 
filter  repeatedly,  till  the  fluid  running  through  gives  no  residue  on 
evaporation  in  a  watch-glass ;  dry  and  weigh. 

The  sulphide  must,  however,  never  be  weighed  as  just  described, 
unless  the  analyst  is  satisfied  that  no  considerable  amount  of  sul- 
phur has  fallen  down  with  it,  as  would  occur  if  the  fluid  contained 
hyponitiic  acid,  a  ferric  salt,  or  any  other  substance  which  decom- 
poses hydrogen  sulphide.  In  case  the  precipitate  does  contain 
much  admixed  sulphur,  the  simplest  process  is  to  convert  it  into 
metallic  silver  (H.  HOSE*).  For  this  purpose  it  is  transferred  to  a 
weighed  porcelain  crucible,  the  filter  ash  is  added,  and  the  whole 
is  heated  to  redness  in  a  stream  of  hydrogen,  the  apparatus- 
described  in  §  108  being  employed.  Results  accurate. 

Should  the  apparatus  in  question  not  be  at  the  operators  dis- 
posal, he  may,  after  complete  washing  of  the  precipitate,  carefully 
rinse  it  into  a  porcelain  dish  (without  injuring  the  weighed  filter), 
heat  it  once  or  twice  with  a  moderately  strong  solution  of  pure 
sodium  sulphite,  retransfer  the  precipitate  (now  freed  from  admixed 
sulphur)  to  the  old  filter,  wash  well,  dry  and  weigh  (J.  LOWE+  >  ; 
or  lie  may  treat  the  dried  precipitate,  together  with  the  filter-ash, 
with  moderately  dilute  chlorine-free  nitric  acid  at  a  gentle  heat, 
till  complete  decomposition  has  been  effected  (till  the  undissolved 
sulphur  has  a  clean  yellow  appearance),  filter,  wash  well,  and  pro- 
ceed according  to  1.  a. 

3.  Determination  as  Silver  Cyanide. 

Mix  the  neutral  solution  of  silver  with  potassium  cyanide,  until 
the  precipitate  of  silver  cyanide  which  forms  at  first  is  redissolved  ; 
add  nitric  acid  in  slight  excess,  and  apply  a  gentle  heat.  If  the 
solution  contains  free  acid,  this  must  be  first  neutralized  with  pot- 
ash or  sodium  carbonate.  After  some  time,  collect  the  precipitated 
silver  cyanide  on  a  weighed  filter,  wash,  dry  at  100°,  and  weigh. 
For  the  properties  of  the  precipitate,  see  §  82.  The  results  are 
accurate. 


*  Pogg.  Annal.  110,  139.  f  Journ.  f.  prakt.  Chem.  77,  73. 


288  DETERMINATION.  [§  115. 

4.  Determination  as  Metallic  Silver. 

Silver  oxide,  silver  carbonate,  &c.,  are  easily  reduced  by  simple 
ignition  in  a  porcelain  crucible.  In  the  reduction  of  salts  of 
organic  acids,  the  crucible  is  kept  covered  at  first,  and  a  moder- 
ate heat  applied ;  after  a  time  the  lid  is  removed,  and  the  heat 
increased,  until  the  whole  of  the  carbon  is  consumed.  For  the 
properties  of  the  residue,  see  §  82.  The  results  are  absolutely 
accurate,  except  as  regards  silver  salts  of  organic  acids;  in  the 
analysis  of  the  latter,  it  not  unfrequently  happens  that  the  reduced 
silver  contains  a  minute  portion  of  carbon,  which  increases  the 
weight  of  the  residue  to  a  trifling  extent. 

If  it  is  desired  to  transform  silver  chloride,  bromide,  or  sulphide 
into  metallic  silver,  for  the  purpose  of  analysis,  they  are  heated  in 
a  current  of  pure  hydrogen  to  redness,  till  the  weight  remains 
constant.  The  process  may  be  conducted  in  a  porcelain  crucible 
or  a  bulb-tube.  In  the  former  case,  the  apparatus  described  p.  251, 
§  108,  is  used;  in  the  latter  the  apparatus  represented  p.  285,  with  the 
substitution,  of  course,  of  hydrogen  for  chlorine.  If  the  bulb-tube 
is  used,  it  must,  after  cooling  and  before  being  weighed,  be  held  in 
an  inclined  position,  so  that  the  hydrogen  may  be  replaced  by  air. 
The  results  are  perfectly  accurate.  Silver  iodide  cannot  be  reduced 
in  this  way. 

5.  Volumetric  Methods. 
I.  GAY-LUSSAC'S. 

This,  the  most  exact  of  all  known  volumetric  processes,  was 
introduced  by  GAY-LUSSAC  as  a  substitute  for  the  assay  of  silver  by 
cupellation,  was  thoroughly  investigated  by  him,  and  will  be  found 
fully  described  in  his  work  on  the  subject.  This  method  has  been 
rendered  still  more  precise  by  the  researches  of  G.  J.  MULDER,  to 
whose  exhaustive  monograph*  I  refer  the  special  student  of  this 
branch.  I  shall  here  confine  myself  to  giving  the  process  so  far 
as  to  suit  the  requirements  of  the  chemical  laboratory,  taking  only 
for  granted  that  the  analyst  has  the  ordinary  measuring  apparatus, 
&c.,  at  his  disposal.  MULDER'S  results  will  be  made  use  of  to  the 
full  extent  possible  under  these  circumstances. 

a.  EEQUISTTES. 

a.  SOLUTION    OF    SODIUM    CHLORIDE.        Take    chemically   pure 

*  Die  Silberprobirmethode  (see  note  p.  167). 


§  115.]  SILVER.  289 

sodium  chloride — either  artificially  prepared  or  pure  rock-salt — 
powder  it  roughly  and  ignite  moderately  (not  to  fusion*).  Now 
dissolve  5*4202  grm.  in  distilled  water  to  1  litre,  measured  at  16°. 
100  c.c.  of  this  solution  contains  a  quantity  of  sodium  chloride 
equivalent  to  1  grm.  of  silver.  The  solution  is  kept  in  a  stoppered 
bottle  and  shaken  before  use. 

ft.  DECIMAL  SOLUTION  OF  SODIUM  CHLORIDE.  Transfer  50  c.c. 
of  the  solution  described  in  a  to  a  500  c.c.  measuring  flask, 
fill  up  to  the  mark  with  distilled  water  and  shake.  Each  c.c. 
of  this  decimal  solution  corresponds  to  '001  grm.  silver.  The 
measuring  must  be  performed  at  16°.  The  solution  is  kept  as  the 
other. 

y.  DECIMAL  SILVER  SOLUTION.  Dissolve  '5  grm.  chemically 
pure  silver  f  in  2  to  3  c.c.  pure  nitric  acid  of  1*2  sp.  gr.,  and  dilute 
the  solution  with  water  exactly  to  500  c.c.  measured  at  16°.  Each 
c.c.  contains  '001  grm.  silver.  The  solution  is  kept  in  a  stoppered 
bottle  and  protected  against  the  influence  of  light. 

d.  TEST-BOTTLES.  These  should  be  of  colorless  glass,  holding 
easily  200  c.c.,  closed  with  well-ground  glass-stoppers,  running  to 
a  point  below.  The  bottles  fit  into  cases  blackened  on  the  inside, 
and  reaching  up  to  their  necks.  In  order  to  protect  the  latter  also 
from  the  action  of  light,  a  black-cloth  cover  is  employed. 

b.  PRINCIPLE. 

Suppose  we  knowT  the  value  of  a  solution  of  sodium  chloride, 
i.e.,  the  quantity  that  is  necessary  to  precipitate  a  given  amount  of 
silver,  say  1  grm.,  we  are  in  the  position,  with  the  aid  of  this  solu- 


*  On  fusion,  if  the  flame  can  in  the  least  way  act  upon  it,  it  takes  an  alkaline 
reaction,  since  under  the  influence  of  vapor  of  water  and  carbon  dioxide,  a  little 
hydrochloric  acid  is  formed  and  escapes,  while  a  corresponding  quantity  of 
sodium  carbonate  remains. 

f  For  the  preparation  of  pure  silver  STAS  recommends  the  following  method: 
Take  crude  silver  nitrate  containing  copper,  fuse  in  order  to  decompose  any 
platinum  nitrate  which  may  be  present,  dissolve  in  dilute  ammonia,  allow  to 
stand  48  hours,  filter  and  dilute  till  the  fluid  does  not  contain  more  than  2  per 
cent,  silver.  Add  ammonium  sulphite  in  excess.  To  ascertain  how  much  sul- 
phite will  be  required  make  a  small  preliminary  test;  as  soon  as  after  heating  the 
blue  solution  loses  all  color,  you  may  be  sure  that  enough  of  the  sulphide  has 
been  added.  Warm  on  a  water-bath  to  60°  or  70°,  when  all  the  silver  will  be 
thrown  down  as  a  metallic  powder,  allow  to  cool  and  wash  by  decantation  with 
diluted  ammonia  till  the  washings  are  free  from  copper  and  sulphuric  acid.  Now 
digest  the  metal  for  several  days  with  strong  ammonia,  wash,  dry,  and  fuse  with 
a  flux  of  borax  and  sodium  nitrate. 


290  DETERMINATION.  [§  115. 

tion,  to  determine  an  unknown  amount  of  silver,  for  if  we  put  x 
for  the  unknown  amount  of  silver,  then 

c.c.  of  solution  used  for  1  grm.  :  c.c.  used  for  x : :  1  grm.  :  x. 

But  if  we  examine  whether  1  mol.  sodium  chloride  dissolved  in 
water  actually  precipitates  1  at.  of  silver  dissolved  in  nitric  acid 
exactly,  we  find  that  this  is  not  the  case.*  On  the  contrary,  the 
clear  supernatant  fluid  gives  a  small  precipitate  both  on  the  addition 
of  a  little  solution  of  sodium  chloride,  and  on  the  addition  of  a 
little  silver  solution,  as  MULDER  has  most  accurately  determined. 
The  value  of  a  solution  of  sodium  chloride  in  the  sense  explained 
above  cannot,  therefore,  be  reckoned  from  the  amount  of  salt  it 
contains,  b^  calculating  1  at.  silver  for  1  mol.  sodium  chloride,  but 
it  can  only  be  obtained  by  experiment.  MULDEK  has  shown  that 
the  temperature  and  the  degree  of  dilution  have  some  influence, 
and  also  that  this  fact  is  to  be  explained  on  the  ground  of  the  sol- 
vent power  of  the  sodium  nitrate  produced  on  the  silver  chloride. 
In  the  solution  thus  formed  we  have  to  imagine  NaNO3  and  NaCl 
with  AgXO3  in  a  certain  state  of  equilibrium,  which  on  the  addition 
of  either  Nad  or  AgNO3  is  destroyed,  silver  chloride  being  pre- 
cipitated. 

From  this  interesting  observation  it  follows,  that  if  to  a  silver- 
solution  we  add  at  first  concentrated  solution  of  sodium  chloride, 
then  decimal  solution  drop  by  drop,  till  the  exact  point  is  reached 
when  no  more  precipitate  appears,  now,  on  addition  of  decimal 
silver-solution,  a  small  precipitate  will  be  again  produced  ;  and  if 
we  add  the  latter  drop  by  drop,  till  the  last  drop  occasions  no  tur- 
bidity, then  again  decimal  solution  of  sodium  chloride  will  give  a 
small  precipitate.  On  noticing  the  number  of  drops  of  both  deci- 
mal solutions  which  are  required  to  pass  from  one  limit  to  the 
other,  we  find  that  the  same  number  of  each  are  used.  Let  us 
suppose  that  we  had  added  decimal  solution  of  sodium  chloride  till 
it  ceased  to  react,  and  had  then  used  20  dropsf  of  decimal  silver- 
solution,  till  this  ceased  to  produce  a  further  turbidity,  we  must 
now  again  add  20  drops  of  decimal  solution  of  sodium  chloride,  in 


*  If  sodium  bromide  or  potassium  bromide  is  used,  complete  precipitation 
would  ensue  on  addition  of  an  equivalent  quantity  of  silver  solution,  since  bro- 
mide of  silver  is  not  at  all  soluble  in  the  supernatant  fluid  (STAS  Compt  rend 
67,  1107). 

f  Twenty  drops  from  MULDER'S  dropping  apparatus  are  equal  to  1  c.c. 


§  115.]  SILVER.  291 

order  to  reach  the  point  at  which  this  ceases  to  react.  Were  we  to 
add  only  10  instead  of  these  20  drops,  we  have  the  neutral  point, 
as  MULDER  calls  it,  i.e.,  the  point  at  which  both  silver  and  sodium 
chloride  produce  equal  precipitates. 

We  have,  therefore,  3  different  points  to  choose  from  for  our 
final  reaction :  a,  the  point  at  which  sodium  chloride  has  just 
ceased  to  precipitate  the  silver ;  5,  the  neutral  point ;  c,  the  point 
at  which  silver-solution  has  just  ceased  to  precipitate  sodium 
chloride.  Whichever  we  may  choose,  we  must  keep  to  it,  l.e.,  we 
must  not  use  a  different  point  in  standardizing  the  sodium  chloride 
solution  and  in  performing  an  analysis.  The  difference  obtained, 
by  using  first  a  and  then  b  is,  according  to  MULDER,  for  1  grin, 
silver,  at  16°,  about '5  mgrm.  silver;  by  employing  first  a  and 
then  c,  as  was  permitted  in  the  original  process  of  GAY-LUSSAC,  the 
difference  is  increased  to  1  mgrm. 

For  our  object,  it  appears  most  convenient  to  consider,  once  for 
all,  the  point  a  as  the  end,  and  never  to  finish  with  the  silver- 
solution.  If  the  point  has  been  overstepped  by  the  addition  of  too 
large  an  amount  of  decimal  solution  of  sodium  chloride,  2  or  3 
c.c.  of  decimal  silver-solution  should  be  added  all  at  once.  The 
end-point  is  then  found  by  carefully  adding  decimal  solution  of 
sodium  chloride  again,  and  the  quantity  of  silver  in  the  silver-solu- 
tion added  is  added  to  the  original  amount  of  silver  weighed  off. 

c.  PERFORMANCE  OF  THE  PROCESS. 

This  is  divided  into  two  operations — a,  the  tit-ration  of  the 
sodium  chloride  solution;  /?,  the  assay  of  the  silver  alloy  to  be 
examined. 

(Y.    TlTRATION    OF    THE    SODIUM    C'lILORIDE    SOLUTION. 

Weigh  off  exactly  from  Tool  to  1*003  grm.  chemically  pure 
silver,*  put  it  into  a  test-bottle,  add  5  c.c.  perfectly  pure  nitric 
acid,  of  1/2  sp.  gr.,  and  heat  the  bottle  in  an  inclined  position  in  a 
water-  or  sand-bath  till  complete  solution  is  effected.  Xow  blow 
out  the  nitrons  f nines  from  the  upper  part  of  the  bottle,  and  after 
it  has  cooled  a  little,  place  it  in  a  stream  of  water,  the  temperature 
of  which  is  about  16°,  and  let  it  remain  there  till  its  contents  are 
cooled  to  this  degree,  wipe  it  dry,  and  place  it  in  its  case. 

Now  fill  the  100  c.c.  pipette  with  the  concentrated  solution  of 
sodium  chloride,  which  is  then  allowed  to  flow  into  the  test-bottle 


*  See  note,  p.  289. 


292  DETERMINATION.  [§  115. 

containing  the  silver-solution*.  Insert  the  glass-stopper  firmly 
(after  moistening  it  with  water),  cover  the  neck  of  the  bottle  with 
the  cap  of  black  stuff  belonging  to  it,  and  shake  violently  without 
delay,  till  the  silver  chloride  settles,  leaving  the  fluid  perfectly 
clear.  Then  take  the  stopper  out,  rub  it  on  the  neck,  so  as  to 
remove  all  silver  chloride,  replace  it  firmly,  and  by  giving  the 
bottle  a  few  dexterous  turns,  rinse  the  chloride  down  from  the 
upper  part.  After  allowing  to  rest  a  little,  again  remove  the 
stopper,  and  add,  from  a  burette  divided  into  TJ¥  c.c.,  decimal 
sodium  chloride  solution,  allowing  the  drops  to  fall  against  the 
lower  part  of  the  neck,  the  bottle  being  held  in  an  inclined 
position.  If,  as  above  directed,  1*001  to  1*008  grm.  silver  have 
been  employed,  the  portions  of  sodium  chloride  solution  at  first 
added  may  be  £  c.c.  After  each  addition,  raise  the  bottle  a  little 
out  of  its  case,  observe  the  amount  of  precipitate  produced,  shake 
till  the  fluid  has  become  clear  again,  and  proceed  as  above,  before 
adding  each  fresh  quantity  of  sodium  chloride  solution.  The 
smaller  the  precipitate  produced,  the  smaller  should  be  the  quan- 
tity of  sodium  chloride  next  added ;  towards  the  end  only  two 
drops  should  be  added  each  time ;  and  quite  at  the  end  read  off 
the  height  of  the  fluid  in  the  burette  before  each  further  addition. 
When  the  last  two  drops  give  no  more  precipitate,  the  previous 
reading  is  the  correct  one. 

If  by  chance  the  point  has  been  overstepped,  and  the  time  has 
been  missed  for  the  proper  reading  off  of  the  burette,  add  2  to  3 
c.c.  of  the  decimal  silver  solution  (the  silver  in  which  is  to  be 
added  to  the  quantity  first  weighed),  and  try  again  to  hit  the  point 
exactly  by  careful  addition  of  decimal  sodium  chloride  solution. 

The  value  of  the  sodium  chloride  solution  is  now  known. 
Reckon  it  to  1  grm.  silver. 

Suppose  we  had  used  for  1*002  grm.  silver,  100  c.c.  of  concen- 
trated and  3  c.c.  of  decimal  sodium  chloride  solution ;  this  makes 
altogether  100*3  of  concentrated  ;  then 

1*002  :  1*000  ::  100*3  :  a? 

v.  =  100*0998 

We  may  without  scruple  put  100*1  for  this  number.     We  now 

*  The  pipette,  having  been  filled  above  the  mark,  should  be  fixed  in  a  support, 
before  the  excess  is  allowed  to  run  out,  otherwise  the  measurings  will  not  be  suffi- 
ciently accurate. 


§  115.]  SILVER.  293 

know  that  100*1  c.c.  of  the  concentrated  solution  of  sodium 
chloride,  measured  at  16°.  exactly  precipitates  1  grin,  of  silver. 
This  relationship  serves  as  the  foundation  of  the  calculation  in 
actual  assaying,  and  must  be  re-examined  whenever  there  is  reason 
to  imagine  that  the  strength  of  the  sodium  chloride  solution  may 
have  altered. 

ft.    THE    ACTUAL    ASSAY    OF    THE    SlLVEK-ALLOY. 

Weigh  oif  so  much  as  contains  about  1  grm.  of  silver,  or  better, 
a  few  mgrm.  more  ;*  dissolve  in  a  test-bottle  in  5  to  7  c.c.  nitric 
acid,  and  proceed  in  all  respects  exactly  as  in  a. 

Suppose  we  had  taken  1-116  grm.  of  the  alloy,  and  in  addition 
to  the  100  c.c.  of  concentrated  sodium  chloride  solution,  had  used 
5  c.c.  of  the  dilute  (=  *5  concentrated),  how  much  silver  would 
the  alloy  contain  ? 

Presuming  that  we  use  the  same  sodium  chloride  solution 
which  served  as  our  example  in  a,  100*1  c.c.  of  which  =  1  grm. 
silver,  then 

100-1  :  100-5  : :  1-000  :  x 

x  =  1-003996  (say  (1-004). 

We  may  also  arrive  at  the  same  result  in  the  following  manner : — 

Nad  Solution. 
For  the  precipitation  of  the  silver  in  the  alloy 

were  used 100*5  c.c. 

For  1  grm.  silver  are  necessary 100*1  c.c. 

Difference -4  c.c. 

There  are,  therefore,  4  mgrm.  of  silrer  present  more  than  a  grm., 
on  the  presumption  that  -1  of  the  concentrated  sodium  chloride 
solution  (—  1  c.c.  of  the  decimal  solution)  corresponds  to  1  mgrm. 


*  In  coins  containing  9  parts  of  silver  and  1  part  of  copper,  therefore  take 
about  1*115  or  1*120.  In  weighing  off  alloys  of  silver  and  copper,  which  do  not 
correspond  to  the  formula  Ag3Cu2  (standard  VoW »)  =  we  must  remember  that 
they  are  never  homogeneous  in  the  mass  ;  thus,  for  instance,  the  pieces  of  metal, 
from  which  coins  are  stamped,  often  show  1-5  to  17  in  a  thousand  more  silver  in 
the  middle  than  at  the  edges.  In  assaying  alloys,  then,  portions  from  various 
parts  of  the  mass  must  be  taken,  in  order  to  get  a  correct  result.  The  inaccuracy, 
however,  proceeding  trom  the  cause  above-mentioned,  can  only  be  completely 
overcome  by  fusing  the  alloy  and  taking  out  a  portion  from  the  well-stirred  mass 
for  the  assay. 


294  DETERMINATION.  [§  115. 

silver.  This  supposition,  although  not  absolutely  correct,  may  he 
safely  made,  for  the  inexactness  it  involves  is  too  minute,  as  is 
evident  from  the  previous  calculation. 

Before  we  can  execute  this  process  exactly,  we  must  know  the 
quantity  of  silver  the  alloy  contains  very  approximately.  In 
assaying  coins  of  known  value  this  is  the  case,  bnt  with  other  silver 
alloys  it  is  usually  not  so.  Under  the  latter  circumstances  an 
approximate  estimation  must  precede  the  regular  assay.  This  is 
performed  by  weighing  off  \  grin,  (or  in  the  case  of  alloys  that  are 
poor  in  silver,  1  grm.),  dissolving  in  3  to  6  c.c.  nitric  acid,  and 
adding  from  the  burette  sodium  chloride  solution, — first  in  larger, 
then  in  smaller  quantities — till  the  last  drops  produce  no  further 
turbidity.  The  last  drops  are  not  reckoned  with  the  rest.  The 
operation  is  conducted,  as  regards  shaking/  &c.,  as  previously 
given.  Suppose  we  had  weighed  off  *5  grm.  of  the  alloy,  and 
employed  25  c.c.  of  the  sodium  chloride  solution — taking  the 
above  supposed  value  of  the  latter- — 

We  have  100-1  :  25  : :  1-000  :  x 

x  =  -249T 

that  is,  the  silver  in  '5  grm.  of  the  alloy ;  and  as  to  the  quantity  of 
alloy  we  have  to  wreigh  off  for  the  assay  proper, 

We  have  '2497  :  1-003  : :  -5  :  x 

x  =±  2-008. 

This  quantity  will,  of  course,  require  more  nitric  acid  for  solution 
than  was  previously  used  (use  10  c.c.).  In  cases  where  the  highest 
degree  of  accuracy  is  not  required,  the  results  afforded  by  this 
rough  preliminary  estimation  will  be  accurate  enough,  if  the 
experiment  is  carefully  conducted,  since  they  give  the  quantity  of 
silver  present  to  within  ^^  or  ^F. 

With  alloys  which  contain  sulphur,  and  with  such  as  consist  of 
gold  and  silver,  and  contain  a  little  tin,  LEVOL*  employs  concen- 
trated sulphuric  acid  (about  25  grm.)  as  solvent.  The  portion  of 
the  alloy  is  boiled  with  it  till  dissolved ;  after  cooling,  the  fluid  is 
treated  in  the  usual  manner.  As,  however,  concentrated  sulphuric, 
acid  fails  to  dissolve  all  the  silver  when  there  is  much  copper 
present,  MAscAzziNif  digests  the  weighed  portion  of  alloy  (which 

*  Annal.  de  Chim.  et  de  Phys.  (3)  44,  347.       \  Chem.  Centralbl.  1857,  300. 


§115.j  SILVKK.  295 

may  contain  small  quantities  of  lead,  tin,  and  antimony,  besides 
gold)  first  with  the  least  possible  amount  of  nitric  acid,  as  long  as 
red  vapors  are  formed;  he  then  adds  concentrated  sulphuric  acid, 
hoils  till  the  gold  has  settled  well  together,  adds  water  after 
<-ooling,  and  then  titrates.  In  the  presence  of  mercury,  tli  • 
chloride  of  that  metal  is  carried  down  with  the  silver,  render  hi"- 

n 

the  method  inaccurate.  If  the  quantity  of  mercury  is  but  small, 
yon  may  get  over  the  difficulty  by  adding  25  c.c.  ammonia  and 
20  c.c.  acetic  acid  (LEVOL).  The  ammonium  acetate  acts  by 
decomposing  the  mercuric  chloride,  and  thus  preventing  its 
precipitation  (DEBRAY*).  If  the  quantity  of  mercury  is  large  the 
addition  of  an  alkali  acetate  is  not  effective,  and  DEBRAY  recom- 
mends to  drive  off  the  mercury  by  igniting  for  four  hours  in  a 
small  crucible  of  gas  carbon  in  a  muffle.  The  presence  of  other 
volatile  metals,  such  as  zinc,  does  not  interfere  with  this  oper- 
ation. 

II.  PISANI'S  METHOD.! 

This  process  depends  on  the  following  reaction  :  a  solution  of 
iodide  of  starch  added  to  a  very  dilute  neutral  solution  of  silver 
nitrate,  forms  silver  iodide  and  silver  hypoiodite.  The  blue  color 
consequently  vanishes,  and  on  continued  addition  of  the  iodide  of 
starch,  the  fluid  does  not  become  permanently  blue  till  all  the  sil- 
ver nitrate  present  is  decomposed  in  the  above  manner.  The 
iodide  of  starch  solution  used  is  therefore  proportional  to  the  quan- 
tity of  silver  nitrate.  Hence,  if  the  value  of  the  iodide  of  starch 
solution  be  determined,  by  allowing  it  to  act  on  a  certain  amount 
of  silver  solution  of  known  strength,  we  shall  be  able  to  estimate 
unknown  quantities  of  silver  with  the  greatest  ease,  provided  that 
the  silver  solution  is  free  from  all  other  substances  which  exert  a 
decomposing  action  on  the  iodide  of  starch.  Besides  the  ordinary 
reducing  agents,  the  following  salts  must  be  especially  mentioned 
as  possessing  this  power :  mercurous  and  mercuric  salts,  stannous 
salts,  manganous,  ferrous,  and  antimonious  salts,  also  auric  chloride 
and  arsenites ;  lead  and  copper  salts,  on  the  other  hand,  do  not 
affect  iodide  of  starch. 

The  iodide  of  starch  is  prepared  as  follows :  make  an  intimate 


*  Compt.  rend.  70,  849.  f  Annal.  d.  Min.  10,  83. 


296  DETEKMI-NATION.  [ 

mixture  in  a  mortar  of  2  grm.  iodine  and  15  grm.  .starch  with  the 
addition  of  6  to  8  drops  of  water,  and  heat  the  slightly-moist  mix- 
ture in  a  closed  flask  in  a  water-bath,  till  the  original  violet-blue 
color  has  passed  into  dark  grayish-blue — it  takes  about  an  hour. 
The  iodide  of  starch  thus  prepared  is  then  digested  with  water ;  it 
dissolves  completely  to  a  deep  bluish-black  fluid. 

The  value  of  this  fluid  is  determined  'by  allowing  it  to  act  on 
10  c.c.  of  a  neutral  solution  of  silver  nitrate,  containing  1  grm.  of 
pure  silver  in  1  litre — the  silver  solution  is  mixed  with  a  little 
pure  precipitated  calcium  carbonate  before  adding  the  iodide  of 
starch.  The  strength  of  this  latter  is  right,  if  50  to  60  c.c.  are 
used  in  this  experiment.  On  adding  it,  at  lirst  the  blue  color  dis- 
appears rapidly,  and  the  fluid  becomes  yellowish  from  the  silver 
iodide.  The  end  of  the  operation  is  attained  as  soon  as  the  fluid  is 
bluish-green.  The  point  is  pretty  easy  to  hit,  and  an  error  of  '5 
c.c.  is  of  no  importance,  as  it  only  corresponds  to  about  '0001  grm. 
silver.  The  calcium  carbonate,  besides  neutralizing  the  free  acid, 
has  the  effect  of  rendering  the  final  change  of  the  color  more  dis- 
tinctly observable.  To  analyze  an  alloy  of  silver  and  copper,  dis- 
solve about  '5  grm.  in  nitric  acid,  dilute  to  100  c.c.  to  lower  the 
color  of  the  copper,  saturate  5  c.c.  with  calcium  carbonate,  and  add 
iodide  of  starch  till  the  coloration  appears.  Or  you  may  deter- 
mine very  approximately  the  amount  of  silver  in  2  c.c.  of  the  solu-~ 
tion,  then  precipitate  the  greater  part  (about  9 9f)  of  the  silver 
from  50  c.c.  of  the  solution  with  standard  solution  of  potassium 
iodide,  and  without  filtering  estimate  the  remainder  of  the  silver 
by  means  of  iodide  of  starch.  If  the  amount  of  silver  to  be  deter- 
mined is  more  than  '020  grm.,  it  is  always  better  to  employ  the 
latter  method.  In  the  case  of  a  nitric  acid  solution  containing  sil- 
ver with  lead,  the  latter  metal  is  first  precipitated  with  sulphuric 
acid  and  filtered  off,  calcium  carbonate  is  added  to  the  filtrate  till 
all  free  acid  is  neutralized,  the  fluid  is  filtered  again  (if  necessary), 
and  lastly,  more  calcium  carbonate  is  added,  and  then  the  iodide  of 
starch.  Very  dilute  solutions  must  be  concentrated,  so  that  one  may 
have  no  more  than  from  50  to  100  c.c.  to  deal  with.  The  method  is 
worthy  of  notice  and  specially  suited  for  the  estimation  of  small 
quantities  of  silver.  "With  such  it  has  afforded  me  perfectly  satis- 
factory results.  Instead  of  the  standard  iodide  of  starch,  a  dilute 
standard  solution  of  iodine  in  potassium  iodide  may  be  equally  well 


§  116.]  LEAD.  .   297 

employed — with  addition  of  starch  solution  (FIELD*).  If  this  is 
used  you  must  bear  in  mind  that  any  substance  which  decomposes 
potassium  iodide  with  separation  of  iodine  will  interfere. 

III.  METHOD  DEPENDING  ON  THE  ACTION  OF  SILVER  NITRATE  ON 

SODIUM    CHLORIDE  IN  THE  PRESENCE  OF  POTASSIUM    CHROMATE. 

This  is  the  reverse  of  the  method  for  the  estimation  of  -chlorine 
§  141  I,  a,  and  will  be  described  in  that  place. 

§116. 

2.  LEAD. 

a.  Solution. 

Few  of  the  lead  salts  are  soluble  in  water.  Metallic  lead,  lead 
oxide,  and  most  of  the  lead  salts  that  are  insoluble  in  water  dissolve 
in  dilute  nitric  acid.  Concentrated  nitric  acid  effects  neither  com- 
plete decomposition  nor  complete  solution,  since,  owing  to  the 
insolubility  of  lead  nitrate  in  concentrated  nitric  acid,  the  first  por- 
tions of  nitrate  formed  protect  the  yet  undecomposed  parts  of  the 
salt  from  the  action  of  the  acid.  For  the  solubility  of  lead  chloride 
and  sulphate,  see  §  83.  As  we  shall  see  below,  the  analysis  of 
these  compounds  may  be  effected  without  dissolving  them,  lead 
iodide  dissolves  readily  in  moderately  dilute  nitric  acid  upon  appli- 
cation of  heat,  with  separation  of  iodine.  Solution  of  potassa  is 
the  only  menstruum  in  which  lead  chromate  dissolves  without 
decomposition. 

b.  Determination. 

Lead  may  be  determined  as  oxide,  sulphate,  chromate,  or  sul- 
phide •  also  by  volumetric  analysis. 
We  may  convert  into 

1.  LEAD  OXIDE  : 

a.  By  Precipitation. 

All  lead  salts  soluble  in  water,  and  those  of  its  salts  which, 
insoluble  in  that  menstruum,  dissolve  in  nitric  acid,  wiih  separa- 
tion of  their  acid. 

b.  By  Ignition. 

a.  Lead  salts  of  readily  volatile  or  decomposable  inorganic  acids. 
/?.  Lead  salts  of  organic  acids. 

*  Chem.  News,  2,  17. 


298  DETERMINATION.  [§  116. 

2.  LEAD  SULPHIDE  : 

All  lead  salts  in  solution. 

3.  LEAD  SULPHATE: 

a.  By  Precipitation. 

The  salts  that  are  insoluble  in  water,  but  soluble  in  nitric  acid, 
whose  acid  cannot  be  separated  from  the  solution. 

b.  By  Evaporation. 

a.  All  the  oxides  of  lead,  and  also  the  lead  salts  of  volatile  acids. 
ft.  Many  of  the  organic  compounds  of  lead. 

4.  LEAD  CHROMATE: 

The  compounds  of  lead  soluble  in  water  or  nitric  acid. 

The  application  of  these  several  methods  must  not  be  under- 
stood to  be  rigorously  confined  to  the  compounds  specially  enu- 
merated under  their  respective  heads ;  thus,  for  instance,  all  the 
compounds  enumerated  sub  1,  may  likewise  be  determined  as  lead 
sulphate ;  and,  as  above  mentioned,  all  soluble  compounds  of  lead 
may  be  converted  into  lead  sulphide  ;  also,  in  lead  sulphate  the  lead 
may  be  without  difficulty  determined  as  sulphide,  Lead  chloride, 
bromide,  and  iodide  are  most  conveniently  reduced  to  the  metallic 
state  in  a  current  of  hydrogen  gas,  in  the  manner  described  §  115 
(Reduction  of  silver  chloride),  if  it  is  not  deemed  preferable  to  dis- 
solve them  in  water,  or  to  decompose  them  by  a  boiling  solution  of 
sodium  carbonate.  If  the  reduction  method  is  resorted  to,  the 
heat  applied  should  not  be  too  intense,  since  this  might  cause  some 
lead  chloride  to  volatilize. 

The  higher  oxides  of  lead  are  reduced  by  ignition  to  the  state 
of  lead  monoxide,  and  may  thus  be  readily  analyzed  and  dissolved. 
Should  the  operator  wish  to  avoid  having  recourse  to  ignition,  the 
most  simple  mode  of  dissolving  the  higher  oxides  of  lead  is  to  act 
upon  them  with  dilute  nitric  acid,  with  the  addition  of  alcohol. 
For  the  methods  of  analyzing  lead  sulphate,  chromate,  iodide,  and 
bromide,  I  refer  to  the  paragraphs  treating  of  the  corresponding 
acids,  in  the  second  part  of  this  section.  To  effect  the  estimation 
of  lead  in  the  oxide  and  in  many  lead  salts,  especially  also  in  the 
sulphate,  the  compound  under  examination  may  be  fused  with 
potassium  cyanide,  and  the  metallic  lead  obtained  well  washed,  and 
weighed.  From  the  sulphide  also  the  greater  portion  of  the  lead 


§  116.]  LEAD.  299 

may   be    separated   by   this   method,    but   never  the   whole   (II. 

ROSE*). 

1.  Determination  as  Oxide. 

a.  By  Precipitation. 

Mix  the  moderately  dilute  solution  with  ammonium  carbonated 
slightly  in  excess,  add  some  caustic  ammonia,  apply  a  gentle  heat, 
allow  to  cool  and  filter  through  a  small  thin  filter.  Wash  with 
pure  water,  dry,  and  transfer  the  precipitate  to  a  watch-glass, 
removing  it  as  completely  as  possible  from  the  filter ;  burn  the 
latter  in  a  weighed  porcelain  crucible.  After  the  crucible  is  cold, 
moisten  the  ash  with  nitric  acid,  allow  it  to  evaporate,  ignite  gently, 
allow  to  cool,  add  the  precipitate  and  ignite  gently  till  all  the  car- 
bonic acid  is  driven  off.  For  the  properties  of  the  precipitate  and 
residue,  see  §  83.  The  results  are  very  satisfactory,  although  gen- 
erally a  trifle  too  low,  owing  to  lead  carbonate  not  being  absolutely 
insoluble,  particularly  in  fluids  rich  in  ammonium  salts  (Expt.  No. 
47,  b). 

b.  By  Ignition. 

Compounds  like  lead  carbonate  or  nitrate  are  cautiously  ignited 
in  a  porcelain  crucible,  until  the  weight  remains  constant.  In  case 
of  lead  salts  of  organic  acids,  the  substance  is  very  gently  heated 
in  a  small  covered  porcelain  crucible,  which  is  included  within  a 
large  one,  also  covered,  until  the  organic  matter  is  completely 
carbonized ;  the  lids  are  then  removed,  when  the  mass  begins  to 
ignite,  and  a  mixture  of  lead  oxide  with  metallic  lead  results, 
which  may  still  contain  unconsumed  carbon.  A  few  pieces  of 
recently  fused  ammonium  nitrate  are  now  thrown  into  the  inner 
crucible,  which  has  previously  been  removed  from  the  flame,  and 
both  are  again  covered.  The  salt  fuses,  oxidizes  the  lead,  and 
converts  it  partly  into  nitrate.  The  whole  is  now  very  gradually 
raised  to  a  red  heat,  until  no  more  fumes  of  hyponitric  acid  escape. 
The  residuary  oxide  is  then  weighed. 

The  results  are  satisfactory. 

2.  Determination  as  Sulphide. 

Lead  may  be  completely  precipitated  from  acid,  neutral  and 


*  Pogg.  Annal.  91,  144. 

f  Ammonium  oxalate,  which  has  been  so  highly  recommended  as  a  precipi- 
tant for  lead,  is  not  so  delicate  as  the  carbonate.  My  experience  in  this  respect 
coincides  with  F.  Mohr's  (Expt.  No.  48). 


300  DETERMINATION.  [§  116. 

alkaline  solutions  by  hydrogen  sulphide,  and  also  from  neutral  and 
alkaline  solutions  by  ammonium  sulphide.  Precipitation  from 
acid  solution  is  usually  employed,  especially  in  separations.  A 
large  excess  of  acid  and  also  warming  should  both  be  avoided. 
The  former  is  prejudicial  to  complete  precipitation  (§  83,  y),  the 
latter  may  readily  occasion  the  re-solution  of  the  sulphide  that  has 
already  been  precipitated.  In  order  to  guard  against  incomplete 
precipitation,  before  filtering,  test  a  portion  of  the  supernatant 
fluid  by  mixing  with  a  relatively  large  quantity  of  strong  hydrogen 
sulphide  water. 

If  the  fluid  contained  no  hydrochloric  acid  or  metallic  chloride, 
the  lead  sulphide  is  pure.  After  it  has  been  filtered  off,  washed 
with  cold  water  and  dried,  it  is  transferred,  together  with  the 
filter-ash,  to  a  porcelain  crucible,  a  little  sulphur  added,  and  ignited 
in  hydrogen  at  gentle  redness  till  its  weight  is  constant.  It  should 
always  be  allowed  to  cool  in  a  current  of  the  gas,  before  being 
weighed.  As  regards  the  apparatus,  see  §  108,  2,  fig.  50.  For  the 
properties  of  the  residue,  see  §  83,  y.  The  results  are  satisfactory 
(II.  ROSE).  The  heat  of  the  ignition  must  not  be  too  low,  or  the 
residue  will  contain  too  much  sulphur,  nor  too  high,  or  the  lead 
sulphide  will  begin  to  volatilize,  and  lead  disulphide  will  also  be 
formed  with  loss  of  hydrogen  sulphide.  Drying  the  precipitate 
at  100°  cannot  be  recommended  (§  83,  y).  If  the  fluid,  on  the 
contrary,  contained  hydrochloric  acid  or  a  metallic  chloride,  the 
lead  sulphide  contains  chloride  which  cannot  be  removed  even  by 
boiling  the  precipitate  with  ammonium  sulphide.  If  the  precipi- 
tate were  treated  as  above,  we  should  obtain  a  tolerably  pure 
sulphide,  but  not  without  loss  from  volatilization  of  chloride.  A 
precipitate  of  this  kind  must  therefore  be  decomposed  with  strong 
hydrochloric  acid,  the  solution  evaporated  to  dryness,  the  residue 
dissolved  by  heating  with  a  concentrated  solution  of  sodium 
acetate,  and  this  solution  diluted  and  poured  with  stirring  into 
excess  of  strong  hydrogen  sulphide  water.  Or  the  lead  chloride 
obtained  may  be  evaporated,  heated  to  200°,  and  weighed  as  such 

(FlNKENER*). 

3.   Determination  as  Sulphate, 
a.   By  Precipitation. 
<x.  Mix  the  solution  (which  should  not  be  over  dilute)  with 

*  Handb.  der  anal.  Chem.  von  H.  ROSE,  6  Aufl.  von  FINKENER,  932. 


3  116.]  LEAD.  301 

moderately  dilute  pure  sulphuric  acid  slightly  in  excess,  and  add 
to  the  mixture  double  its  volume  of  common  alcohol ;  wait  a  few 
hours,  to  allow  the  precipitate  to  subside ;  filter,  wash  the  precipi- 
tate with  common  alcohol,  dry,  and  ignite  after  the  method 
described  in  §  53.  Though  a  careful  operator  may  use  a  platinum 
crucible,  still  a  thin  porcelain  crucible  is  preferable.  See  also  the 
remarks,  1,  a. 

/3.  In  cases  where  the  addition  of  alcohol  is  inadmissible,  a 
greater  excess  of  sulphuric  acid  must  be  used,  and  the  precipitate, 
which  is  allowed  some  time  to  subside,  filtered,  and  washed  first 
with  water  acidulated  with  a  few  drops  of  sulphuric  acid,  then 
repeatedly  with  alcohol.  The  remainder  of  the  process  is  con- 
ducted as  in  a. 

If  the  fluid  contained  nitric  acid,  whether  alcohol  is  used  or 
not,  it  is  advisable  to  evaporate  on  the  water-bath  after  the 
addition  of  the  sulphuric  acid,  till  the  nitric  acid  has  escaped, 
otherwise  the  precipitation  will  not  be  complete.  If  the  fluid 
contained  hydrochloric  acid  or  a  metallic  chloride,  lead  chloride  is 
thrown  down  with  the  sulphate.  In  this  case  you  must  either 
•evaporate  the  fluid  with  excess  of  sulphuric  acid  and  heat  the 
residue  till  sulphuric  acid  fumes  escape  to  drive  off  the  hydro- 
chloric acid,  or  you  must  treat  the  precipitate  and  filter-ash  in  the 
'Crucible  with  concentrated  sulphuric  acid,  evaporate  and  ignite  to 
.convert  it  into  pure  lead  sulphate  (FINKENER*). 

For  the  properties  of  the  precipitate,  see  §  83.  The  method  a 
gives  accurate  results ;  those  obtained  by  ft  are  less  exact  (a  little 
too  low),  but  still  however  satisfactory,  if  the  directions  given  are 
adhered  to.  If,  on  the  contrary,  a  proper  excess  of  sulphuric  acid 
is  not  added,  in  the  presence,  for  instance,  of  ammonium  salts,  the 
lead  is  not  completely  precipitated,  and  if  pure  water  is  used  for 
washing,  decided  traces  of  the  precipitate  are  dissolved. 

b.  By  Evaporation. 

a.  Put  the  substance  into  a  weighed  dish,  dissolve  in  dilute 
nitric  acid,  add  moderately  dilute  pure  sulphuric  acid  slightly  in 
excess,  and  evaporate  at  a  gentle  heat ;  at  last  high  over  the  lamp, 
until  the  excess  of  sulphuric  acid  is  completely  expelled.  In  the 
absence  of  organic  substances,  the  evaporation  may  be  effected 


*  Handb.  der  anal.  Chem.  von  H.  ROSE,  6  Aufl.  von  FESKENER,  932. 


302  DETERMINATION.  [§  116. 

without  fear  in  a  platinum  dish ;  but  if  organic  substances  are 
present,  a  light  porcelain  dish  is  preferable.  "With  due  care  in  the 
process  of  evaporation,  the  results  are  perfectly  accurate. 

/?.  Organic  compounds  of  lead  are  converted  into  the  sulphate 
by  treating  them  in  a  porcelain  crucible,  with  pure  concentrated 
sulphuric  acid  in  excess,  evaporating  cautiously  in  the  well-covered 
crucible,  until  the  excess  of  sulphuric  acid  is  completely  expelled, 
and  igniting  the  residue.  Should  the  latter  not  look  perfectly 
white,  it  must  be  moistened  once  more  with  sulphuric  acid,  and 
the  operation  repeated.  The  method  gives,  when  conducted  with 
great  care,  accurate  results  ;  a  trifling  loss  is,  however,  usually  in- 
curred, the  escaping  sulphur  dioxide  and  carbon  dioxide  gases 
being  liable  to  carry  away  traces  of  the  salt. 

4.  Determination  as  Lead  Chromate. 

If  the  solution  is  not  already  distinctly  acid  render  it  so  with 
acetic  acid,  then  add  potassium  dichromate  in  excess,  and,  if  free 
nitric  acid  is  present,  add  sodium  acetate  in  sufficient  quantity  to 
replace  the  free  nitric  acid  by  free  acetic  acid ;  let  the  precipitate 
subside  at  a  gentle  heat,  and  collect  on  a  weighed  iilter  dried  at 
100°,  wash  with  water,  dry  at  100°,  and  weigh.  The  precipitate 
may  also  be  ignited  according  to  §  53,  but  in  this  case  care  must  be 
taken  that  hardly  any  of  the  salt  remains  adhering  to  the  paper, 
and  that  the  heat  is  not  too  high.  For  the  properties  of  the 
precipitate,  see  §  93,  2.  The  results  are  accurate.  (Expt.  No.  76.) 

5.  Determination  of  Lead  by  Volumetric  Analysis. 
Although  there  is  no  lack  of  proposed  methods  for  the  volu- 
metric estimation  of  lead,  we  are  still  without  a  really  good  method 
for  practical  purposes,  that  is,  a  method  which  can  be  generally 
employed,  and  which  is  at  the  same  time  simple  and  exact.     For 
the  present,  therefore,  in  almost  all  cases   the  gravimetric  deter- 
mination of  lead  is  to  be  preferred  to  the  volumetric.    On  my  own 
part,  at  least,  I  cannot  see  that  it  is  easier  or  any  better,  when  one 
has  the  precipitate  washed,  to  subject  it  to  a  volumetric  process — 
whereby  the  accuracy  is  necessarily  diminished — instead  of  igniting 
it  gently  and  weighing.     For  this  reason,  the  better  volumetric 
methods  will  be  .but  briefly  described,  the  rest  being  altogether 
omitted. 

a.  The  solution  of  the  normal  lead  salt  must  be  free  from 
alkali  salts,  more  especially  from  ammonium  salts.  It  is  precipi- 


§  116.]  LEAD.  303 

tated  with  oxalic  acid  (not  with  ammonium  oxalate),  the  well- 
washed  precipitate  is  dissolved  in  nitric  acid,  sulphuric  acid  added, 
and  the  oxalic  acid  in  the  solution  determined  by  potassium 
permanganate  (§  137)  HEMPEL. 

b.  II.  SCHWARZ'S   method.*     To  the  nitric  acid  solution  add 
ammonia  or  sodium  carbonate,  as  long  as  the  precipitate  redissolves 
on  shaking,  mix  with  sodium  acetate  in  not  too  small  quantity,  and 
then  run  in  from  a  burette  a  solution  of  potassium  dichromate 
(containing  14'761  gnu.  in  the  litre)  till  the  precipitate  begins  to 
settle  rapidly.     ]S"ow  place  on  a  porcelain  plate  a  number  of  drops 
of  a  neutral  solution  of  silver  nitrate,  and  proceed  with  the  addition 
of  the  chromate,  two  or  three  drops  at  a  time,  stirring  carefully 
after  each  addition.     When  the  precipitate  has  settled  tolerably 
clear,  which  takes  only  a  few  seconds,  remove  a  drop  of  the  super- 
natant liquid  and  mix  it  with  one  of  the  drops  of  silver  solution 
on  the  plate.     A  small  excess  of  chromate  gives  at  once  a  distinct 
red  coloration  ;  the  precipitated  lead  chromate  does  not  act  on  the 
silver  solution,  but  remains  suspended  in  the  drop.     The  number 
of  c.c.  of  solution  of  chromate  used  (minus  *1  which  SCHWARZ 
deducts  for  the  excess)  multiplied  by  '0207  =  the  quantity  of  lead. 
If  the  fluid  appear  yellow  before  the  reaction  with  the  silver  salt 
occurs,  sodium  acetate  is  wanting.     In  such  a  case  first  add  more 
sodium  acetate,  then   1  c.c.  of  a  solution  containing  '0207  lead  in 
1  c.c.,  complete  the   process  in   the  usual  way,  and  deduct  1  c.c. 
from  the  quantity  of  chromate  used  on  account  of  the  extra  lead 
added.     Any  iron  present  must  be  in  the   form  of  a  ferric  salt ; 
metals  whose  chromates  are  insoluble,  must  be  removed  before 
the  method  can  be  employed. 

c.  The  lead  is  precipitated  according  to  1,  #,  the  carbonate  (its 
composition  is  a  matter  of  indifference   in   the   present   case)   is 
washed,  dissolved  in  a  measured  quantity  of  standard  nitric  acid, 
and  a  neutral  solution  of  sodium  sulphate  added,  whereby  lead 
sulphate  is  precipitated  and   an   equivalent    quantity    of   sodium 
nitrate   formed.     If  the  nitric  acid   still  free  is  now  determined 
with  standard  alkali,  we  shall   find  the  quantity  of  acid   that  has 
been  neutralized  by  means  of  the  lead,  from  which  the  amount  of 
lead  may  be  calculated.     You  may  also  determine  the  free  nitric 
acid  by  adding  standard  sodium  carbonate  till,  the  vessel  being  on 

*  Dingl.  polyt.  Journ.  169,  284. 


304  DETERMINATION.  [§  117. 

a  black  surface,  a  permanent  turbidity  is  visible.     Results  good 
(F.  MOHR*). 

§117. 
3.  MERCURY  IN  MERCUKOUS  COMPOUNDS. 

a.  Solution. 

Mercurous  oxide  and  mercurous  salts  may  generally  be  dissolved 
by  means  of  dilute  nitric  acid,  but  without  application  of  heat  if 
conversion  into  mercuric  compounds  is  to  be  avoided.  If  all  that 
is  required  is  to  dissolve  the  mercury,  the  easiest  way  is  to  warm 
the  substance  for  some  time  with  nitric  acid,  then  add  hydrochloric 
-acid,  drop  by  drop,  and  continue  the  application  of  a  moderate  heat 
until  a  perfectly  clear  solution  is  produced,  which  now  contains  all 
the  mercury  in  form  of  mercuric  salts.  Heating  the  solution  to 
boiling,  or  evaporating,  must  be  carefully  avoided,  as  otherwise 
mercuric  chloride  may  escape  with  the  steam. 

1}.  Determination. 

If  it  is  impracticable  to  produce  a  solution  of  the  mercurous 
compound  without  formation  of  mercuric  salts,  it  becomes  neces- 
sary to  convert  the  mercury  completely  into  mercuric  salts,  when 
it  may  be  determined  as  directed  §  118.  But  if  a  solution  of  a 
mercurous  compound  has  been  obtained,  quite  free  from  mercuric 
salts,  the  determination  of  the  mercury  may  be  based  upon  the 
insolubility  of  mercurous  chloride,  and  effected  either  gravimetri- 
cally  or  volumetrically.  The  process  of  determining  mercury, 
described  §  118, 1,  #,  may,  of  course,  be  applied  equally  well  in  the 
•case  of  mercurous  compounds. 

1.  Determination  as  Mercurous  Chloride. 

Mix  the  cold  highly  dilute  solution  with  solution  of  sodium 
•chloride,  as  long  as  a  precipitate  forms  ;  let  the  precipitate  subside, 
collect  on  a  weighed  filter,  dry  at  100°,  and  weigh.  For  the 
properties  of  the  precipitate,  see  §  84.  Results  accurate.  If  the 
mercurous  solution  contains  much  free  nitric  acid,  the  greater  part 
of  this  should  be  neutralized  with  sodium  carbonate  before  adding 
the  sodium  chloride. 


*  His  Lehrbuch  der  Titrirmethode,  3  Aufl.  115. 


§  117.]  MERCURY   IN   MERCUROUS   COMPOUNDS.  305 

2.  Volumetric  Methods. 

Several  methods  have  been  proposed  under   this   head:   the 
following  are  those  which  are  most  worthy  of  recommendation : — 

a.  Mix  the  cold  solution  with  decinormal  solution  of  sodium 
chloride  (§  141,  J,  a\  until  this  no  longer  produces  a  precipitate, 
and  is  accordingly  present  in  excess ;  filter  and  wash  thoroughly, 
taking  care,  however,  to  limit  the  quantity  of  water  used ;  add  a 
few  drops  of  solution  of  potassium  chromate,  then  pure  sodium 
carbonate,  sufficient  to  impart  a  light  yellow  tint  to  the  fluid,  and 
determine  by  means  of  solution  of  silver  nitrate  (§  141,  J,  a)  the 
quantity  of  sodium  chloride  in  solution,  consequently  the  quantity 
which  has  been  added  in  excess ;  this  shows,  of  course,  also  the 
amount  of  sodium  chloride  consumed  in  effecting  the  precipitation. 
One  mol.  of  Hg,O  is  reckoned  for  2  mols.  of  NaCl,  consequently 
for  every  c.c.  of  the  decinormal  solution  of  sodium  chloride,  '0208 
grin,  of  mercurous  oxide.     As  filtering  and  washing  form  indis- 
pensable parts  of  the  process,  this  method  affords  no  great  advan- 
tage  over  the   gravimetric;    however,   the   results   are    accurate 
(FK.  MOHK*).     The  two  methods,  1  and  2,  a,  may  also  be  advan- 
tageously combined. 

b.  Precipitate  the  mercurous  solution,  f  according  to  1,  with 
sodium  chloride  in  a  stoppered  bottle,  allow  to  subside,  filter,  wash, 
push  a  hole  through  the  bottom  of  the  filter,  and  rinse  the  precipi- 
tate into  the  bottle,  which  usually  has  some  of  the  washed  mercu- 
rous chloride  adhering  to  its  inside.     Add  a  sufficient  quantity  of 
solution  of  potassium  iodide,  together  with  standard  iodine  solution 
(to  1  grm.  HgaCl.j  about  2*5  grm.  KI  and  100  c.c.  ^  normal  iodine 
solution^),  insert  the  stopper,  and  shake  till  the  precipitate  has 
entirely  dissolved  (Hg2Cl2+  6KI  +  21  =  2[HgI2(KI)2]  +  2KC1). 
As  iodine  is  in  excess,  the  solution  appears  brown.     If  any  mercu- 
ric iodide  separates,  add  potassium  iodide  to  redissolve  it.     Now 
add  from  a  burette  solution  of  sodium  thiosulphate — correspond- 
ing1 to  decinormal  iodine  solution — till  the  fluid  is  decolorized  and 

o 

appears  like  water,  transfer  to  a  measuring  flask,  rinse  and  fill  up 
to  the  mark,  shake,  take  out  an  aliquot  part,  add  starch  paste  to  it, 
and  determine  the  excess  of  sodium  thiosulphate  with  -fa  iodine 
solution.  After  multiplying  by  the  proper  number,  add  the  c.c. 
originally  employed,  subtract  the  c.c.  of  thiosulphate  used,  and 

*  Lehrbuch  der  Titrirmethode,  3  Aufl.  395. 

f  If  oxide  of  mercury  is  also  present,  see  §  118,  2.  \  See  §  146,  2. 


306  DETERMINATION.  [§  118, 

reckon  the  quantity  of  mercury  from  the  remainder.     2  at.  iodine 
—  1  mol.  Hg2Cl2.     Results  good  (HEMPEL  *). 

§118. 
4.  MEKCUKY  IN  MEKCUKIO  COMPOUNDS. 

a.  Solution. 

Mercuric  oxide,  and  those  mercuric  compounds  which  are 
insoluble  in  water,  are  dissolved,  according  to  circumstances,  in 
hydrochloric  acid  or  in  nitric  acid.  Mercuric  sulphide  is  heated 
with  hydrochloric  acid,  and  nitric  acid  or  potassium  chlorate  added 
until  complete  solution  ensues;  it  is,  however,  most  readily  dis- 
solved by  suspending  it  in  dilute  potassa  and  transmitting  chlorine, 
at  the  same  time  gently  warming  (H.  ROSE).  When  a  solution  of 
mercuric  chloride  is  evaporated  on  the  water-bath,  mercuric  chlo- 
ride escapes  with  the  aqueous  vapor. 

5.  Determination. 

Mercury  may  be  weighed  in  the  metallic  state,  or  as  mercurous 
chloride,  mercuric  sulphide,  or  mercuric  oxide  (84) ;  in  separations 
it  is  sometimes  determined  as  loss  on  ignition.  It  may  also  be 
estimated  volume trically. 

The  three  first  methods  may  be  used  in  almost  all  cases ;  the 
determination  as  mercuric  oxide,  on  the  contrary,  is  possible  only 
in  mercurous  or  mercuric  nitrates.  The  methods  by  which  the 
mercury  is  determined  as  mercurous  chloride  or  mercuric  sulphide 
are  to  be  preferred  before  those  in  which  it  is  separated  in  the 
metallic  form.  The  volumetric  method  5,  is  of  very  limited  appli- 
cation. The  mercurous  chloride  obtained  by  method  2,  instead  of 
being  weighed,  may  be  determined  volumetrically  as  in  §  117,  2, 1. 

1.  Determination  as  Metallic  Mercury* 

a.  In  the  Dry  Way. 

The  process  is  conducted  in  the  apparatus  illustrated  by  fig.  54, 

Take  a  tube  18  inches  long,  and  about  4  lines  wide,  made 
of  difficultly  fusible  glass,  and  sealed  at  one  end.  First  put  into 
the  tube  a  mixture  of  sodium  hydrogen  carbonate  and  powdered 
chalk,  then  a  layer  of  quick-lime ;  these  two  will  occupy  the  space 
from  a  to  b.  (Let  the  mixture  for  generating  carbon  dioxide  take 
up  about  two  inches.)  Then  add  the  intimate  mixture  of  the  sub- 

*Annal.  d.  Chem.  u.  Pharm.  110,  176. 


$118.  j  MKLHUKY    IN    MERCURIC    COMPOUNDS.  307 


stance  with  an  excess  of  quick-lime  (&-<?),  then  the  lime-rinsings  of 
the  mortar  (c-d),  then  a  layer  of  quick-lime  (d-e\  and  lastly,  a 
loose  stopper  of  asbestus  (e-f).  The  anterior  end  of  the  tube  is 
then  drawn  out,  and  bent  at  a  somewhat  obtuse  angle.  The 
manipulations  in  the  processes  of  mixing  and  filling  being  the 
same  as  in  organic  analysis,  they  will  be  found  in  detail  in  the 
chapter  on  that  subject. 

A  few  gentle  taps  upon  the  table  are  sufficient  to  shake  the 
contents  of  the  tube  down  so  as  to  leave  a  free  passage  through  the 
whole  length  of  the  tube.  The  tube,  so  prepared  and  arranged,  is 
now  placed  in  a  combustion  furnace,  the  point  being  inserted  into 
a  flask  containing  water,  the  surface  of  which  it  should  just  touch, 
so  that  the  opening  may  be  just  closed. 

The  tube  is  no\v  surrounded  with  red-hot  charcoal,  in  the  same 
way  as  in  organic  analysis,  proceeding  slowly  from  e  to  <z,  the  last 
traces  of  mercurial  vapor  being  expelled  by  heating  the  mixture  at 


Fig.  54. 

the  sealed  end  of  the  tube.  Whilst  the  tube  still  remains  in  a  state 
of  intense  ignition,  the  neck  is  cut  off  at/",  and  carefully  and  com- 
pletely rinsed  into  the  receiving  flask,  by  means  of  a  washing-bottle. 
The  small  globules  of  mercury  which  have  distilled  over  are  united 
into  a  large  one,  by  agitating  the  flask,  and,  after  the  lapse  of  some 
time,  the  perfectly  clear  water  is  decanted,  and  the  mercury  poured 
into  a  weighed  porcelain  crucible,  where  the  greater  portion  of  the 
water  still  adhering  to  it  is  removed  with  blotting-paper.  The 
mercury  is  then  finally  dried  under  a  bell-jar,  over  concentrated 
sulphuric  acid,  until  the  weight  remains  constant.  Heat  must  not 
be  applied.  For  the  properties  of  the  metal,  see  §  84.  In  the 
case  of  sulphides,  in  order  to  avoid  the  presence  of  vapor  of  water 
in  the  tube,  which  would  give  rise  to  the  formation  of  sulphuretted 
hydrogen,  the  mixture  of  sodium  hydrogen  carbonate  and  chalk  is 
replaced  by  magnesite.  Mercuric  iodide  cannot  be  completely 


308  DETERMINATION.  [§  118. 

decomposed  by  lime.  To  analyze  this  in  the  dry  way,  substitute 
finely  divided  metallic  copper  for  the  lime  (II.  ROSE*).  The  accu- 
racy of  the  results  is  entirely  dependent  upon  the  care  bestowed. 
The  most  highly  accurate  results  are,  however,  obtained  by  the 
application  of  the  somewhat  more  complicated  modification  adopted 
by  ERDMANN  and  MARCH  AND  for  the  determination  of  the  atomic 
weight  of  mercury  and  of  sulphur.  For  the  details  of  this  modi- 
fied process,  I  refer  to  the  original  essay,  f  simply  remarking  here, 
that  the  distillation  is  conducted,  in  a  combustion-tube,  in  a  cur- 
rent of  carbon  dioxide  gas,  and  that  the  distillate  is  received  in  a 
weighed  bulb  apparatus  with  the  outer  end  filled  with  gold-leaf,  to 
insure  the  condensation  of  every  trace  of  mercury  vapor.  This 
way  of  receiving  and  condensing  may  be  employed  also  in  the 
analysis  of  amalgams  (KoNiaJ). 

I.  In  the  Wet  Way. 

The  solution,  free  from  nitric  acid,  and  mixed  with  free  hydro- 
chloric acid,  is  precipitated,  in  a  flask,  with  an  excess  of  a  clear 
solution  of  stannous  chloride,  containing  free  hydrochloric  acid ; 
the  mixture  is  boiled  for  a  short  time,  and  then  allowed  to  cool. 
After  some  time,  the  perfectly  clear  supernatant  fluid  is  decanted 
from  the  metallic  mercury,  which,  under  favorable  circumstances, 
will  be  found  united  into  one  globule ;  if  this  is  the  case,  the 
globule  of  mercury  may  be  washed  at  once  by  decantation,  first 
with  water  acidulated  with  hydrochloric  acid,  and  finally  with  pure 
water ;  it  is  dried  as  in  a. 

If,  on  the  other  hand,  the  particles  of  the  mercury  have  not 
united,  their  union  in  one  globule  may  as  a  rule  be  readily  effected 
by  boiling  a  short  time  with  some  moderately  dilute  hydrochloric 
acid  mixed  with  a  few  drops  of  stannous  chloride  (having,  of 
course,  previously  removed  by  decantation  the  supernatant  clear 
fluid).  For  the  properties  of  metallic  mercury,  see  §  84. 

Instead  of  stannous  chloride,  other  reducing  agents  may  be 
used,  especially  phosphorous  acid  at  a  boiling  temperature.  This 
method  gives  accurate  results  only  when  conducted  with  the 
greatest  care.  In  general,  a  little  mercury  is  lost  (Comp.  Expt. 
•No.  77). 


*  Pogg.  Annal.  110,  546. 

f  Journ.  f.  prakt.  Chem.  31,  385;  also  Pharm.  Centralbl.  1844,  354. 

\  Journ.  f .  prakt.  Chem.  70,  64. 


§  118.]  MERCURY    IN    MERCURIC    COMPOUNDS.  309 

2.  Determination  as  Mercurmis  Chloride. 

a.  After  II.  HOSE.*  Mix  the  mercuric  solution  (which  may 
contain  nitric  acid)  with  hydrochloric  acid  and  excess  of  phospho- 
rous acid  (obtained  by  the  deliquescence  of  phosphorus  in  moist 
air),  allow  to  stand  for  12  hours  in  the  cold  or  at  a  very  gentle 
heat  (at  all  events  under  60°),  collect  the  mercury,  now  completely 
separated  as  mercurous  chloride,  on  a  weighed  filter,  wash  with 
hot  water,  dry  at  100°,  and  weigh.  Results  perfectly  satisfactory. 

3.  Determination  as  Mercuric  Sulphide. 

The  solution  is  sufficiently  diluted,  acidulated  with  hydrochloric 
acid,  and  precipitated  with  clear  saturated  hydrogen  sulphide  water 
(or  in  the  case  of  large  quantities,  by  passing  the  gas) ;  filter  after 
allowing  the  precipitate  a  short  time  to  deposit,  wash  quickly  with 
cold  water,  dry  at  100°,  and  weigh.  Results  very  satisfactory. 

If  from  any  cause  (e.g.  presence  of  ferric  salts,  free  chlorine,  or 
the  like)  the  precipitate  should  contain  free  sulphur,  the  filter  is 
spread  out  on  a  glass  plate,  the  precipitate  removed  to  a  porcelain 
dish  by  the  aid  of  a  jet  from  the  wash-bottle,  and  warmed  for  some 
time  with  a  moderately  strong  solution  of  sodium  sulphite.  The 
filter,  having  been  in  the  mean  while  somewhat  dried  on  the  glass 
plate,  is  replaced  in  the  funnel,  the  supernatant  fluid  is  poured  on 
to  it,  the  treatment  with  sodium  sulphite  is  repeated,  and  the  pre- 
cipitate (now  free  from  sulphur)  is  finally  collected  on  the  filter, 
washed,  dried,  and  weighed.  Results  very  good  (J.  LowEf). 

Should  the  quantity  of  sulphur  mixed  with  the  precipitate  be 
not  very  large,  it  may  be  removed  also  as  follows :  the  precipitate 
is  first  washed  with  water,  then  twice  with  strong  alcohol,  then 
repeatedly  with  carbon  disulphide,  till  a  few  drops  of  the  washings 
evaporate  on  a  watch-glass  without  leaving  a  residue.  (The  pre- 
cipitate is  retained  on  the  filter  throughout  this  operation.) 

Properties  of  mercuric  sulphide,  §  84 

4.  Determination  as  Oxi.de. 

In  the  mercurous  and  mercuric  salts  of  the  nitrogen  acids,  the 
metal  may  be  very  conveniently  determined  in  the  form  of  mer- 
curic oxide  (MARIGNAC*).  For  this  purpose,  the  salt  is  heated  in 

*  Fogg.  Annal.  110?  529. 

f  Journ.  f.  prakt.  Chem.  77,  73. 

$  Jahresber.  von  Liebig  u.  Kopp,  1849,  594. 


310  DETERMINATION.  [§  118. 

a  bulb-tube,  of  which  the  one  end,  drawn  out  to  a  point,  dips  under 
water,  the  other  end  being  connected  with  a  gasometer,  by  means 
of  which  dry  air  is  transmitted  through  the  tube,  as  long  as  the 
application  of  heat  is  continued.  In  this  way-  complete  decomposi- 
tion of  the  salt  is  readily  effected,  without  reaching  the  tempera- 
ture at  which  the  oxide  itself  would  be  decomposed. 

5.  Volumetric  Methods. 

After  J.  J.  SCHERER.*  Mercuric  nitrate  or  chloride  may  be 
directly  determined  with  sodium  thiosulphate.  The  reactions  are 
as  follows :  2H2O  +  3Hg(NO3)2  +  2Na2S2O3  =  (HgS)2  -  Hg(lTO3)2+ 
2JSTa,S04  +  4HN03;  or,  2H2O  +  3IIgCl2  +  2Na2S2O8  =  (HgS),  -  Hg 
C12  + 2Na2SO4 +  4HC1.  The  process  is  conducted  as  follows  in 
the  case  of  mercuric  nitrate :  Mix  the  highly  dilute  solution  with 
a  little  free  nitric  acid  in  a  tall  glass,  and  add  drop  by  drop  solution 
of  sodium  thiosulphate — 12*4  grm.  in  a  litre.  Each  drop  produces 
an  intense  yellow  cloud,  which  on  shaking  quickly  subsides  in  the 
form  of  a  heavy  flocculent  precipitate  (HgS)2  •  Hg(NOs)s.  In  order 
to  distinguish  clearly  the  exact  end  of  the  reaction,  SCHERER 
recommends  to  transfer  the  fluid  towards  the  end  to  a  measuring 
flask,  to  take  out  -J  or  -J  of  the  clear  fluid  and  to  finish  with  this. 
The  portion  of  thiosulphate  last  used  is  multiplied  by  3  or  2,  as 
the  case  may  be,  and  added  to  the  quantity  first  used.  1  c.c.  of 
the  solution  corresponds  to  *015  mercury,  or  -0162  mercuric  oxide. 
The  relation  is  not  changed  even  when  the  fluid  contains  another 
acid  (sulphuric,  phosphoric). 

In  the  case  of  mercuric  chloride,  the  highly  dilute  solution  is 
mixed  with  a  little  hydrochloric  acid  and  warmed,  nearly  to  boil- 
ing, before  beginning  to  add  the  sodium  thiosulphate.  At  first  a 
white  turbidity  is  formed,  then  the  precipitate  separates  in  thick 
flocks.  When  the  solution  begins  to  appear  transparent,  the  pre- 
cipitant is  added  more  slowly.  In  order  to  hit  the  end  of  the 
reaction  exactly,  small  portions  must  be  filtered  off  towards  the 
close.  The  precipitate  must  be  completely  white ;  if  too  much 
thiosulphate  has  been  added,  it  is  gray  or  blackish,  and  the  experi- 
ment must  be  repeated.  SCHERER  obtained  very  accurate  results. 
Of  course  no  other  metals  must  be  present  that  exert  a  decompos- 
ing action  on  sodium  thiosulphate. 

*  His  Lehrbuch  der  Chemie,  i.  513. 


-§  119.]  COPPER.  311 

§ 

5. 

a.  Solution 

Many  cupric  salts  dissolve  in  water.  Metallic  copper  is  best 
dissolved  in  nitric  acid.  Cupric  oxide,  and  those  cupric  salts  which 
are  insoluble  in  water,  may  be  dissolved  in  nitric,  hydrochloric,  or 
sulphuric  acid.  Cupric  sulphide  is  treated  with  fuming  nitric  acid, 
or  it  is  heated  with  moderately  dilute  nitric  acid,  until  the  separated 
sulphur  exhibits  a  pure  yellow  tint ;  addition  of  a  little  hydro- 
chloric acid  or  potassium  chlorate  greatly  promotes  the  action  of 
the  dilute  acid. 

l>.   Determination. 

Copper  may  be  weighed  in  the  form  of  cupric  oxide,  or  in  the 
metallic  state,  or  as  cuprous  sulphide  (§85).  Into  the  form  of. 
cupric  oxide  it  is  converted  by  precipitation,  or  ignition,  sometimes 
with  previous  precipitation  as  sulphide.  The  determination  as 
cuprous  sulphide  is  preceded  usually  by  precipitation  either  as 
cupric  sulphide  or  as  cuprous  sulphocyanate.  Copper  may  be  deter- 
mined also  by  various  volumetric  and  indirect  methods. 

We  may  convert  into 

1.  CUPRIC  OXIDE  : 

a.  By  Precipitation  as  hydrated  cupric  oxide  and  subsequent 
ignition :  All  cupric  salts  soluble  in  water,  and  also  those  insoluble 
salts,  the  acids  of  which  may  be  removed  upon  solution  in  nitric 
acid,  provided  no  non-volatile  organic  substances  be  present. 

1.  By  Precipitation,  preceded  by  Ignition  of  the  compound : 
Such  of  the  salts  enumerated  under  a  as  contain  a  non-vblatile 
organic  substance,  thus  more  particularly  cupric  salts  of  non-vola- 
tile organic  acids. 

c.  By  Ignition :  Cupric  salts  of  oxygen  acids  that  are  readily 
volatile  or  decomposable  at  a  high  temperature  (cupric  carbonate, 
cupric  nitrate). 

2.  METALLIC  COPPER  :   Copper  in  all  solutions  free  from  other 
metals  precipitable  by  zinc  or  the  galvanic  current,  also  the  oxides 
of  copper. 

3.  CUPROUS  SULPHIDE  :  Copper  in  all  cases  in  which  no  other 
metals  are  present  that  are  precipitable  by  hydrogen  sulphide  or 
potassium  sulphocyanate. 


312  DETERMINATION.  [§  119. 

Of  the  several  methods  of  effecting  the  estimation  of  copper, 
No.  3  is  particularly  to  be  recommended  for  use  in  laboratories ; 
method  2  is  also  very  convenient,  and  well  adapted  for  assaying. 
Of  the  volumetric  methods,  one  is  suited  for  technical  purposes, 
the  other  for  the  estimation  of  small  quantities  of  copper.  For 
technical  purposes  there  are,  besides,  also  several  colorimetric 
methods,  proposed  by  HEINE.,  VON  HUBERT,  JACQUELAIN,  A.  MUL- 
LER,  and  others,  which  are,  all  of  them,  based  upon  the  comparison 
of  an  ammoniacal  solution  of  copper,  of  unknown  strength,  with 
others  of  known  strength.* 

LEVOL'S  indirect  method  of  estimating  copper,  which  is  based 
upon  the  diminution  of  weight  suffered  by  a  strip  of  copper  when 
digested  in  a  close-stoppered  flask  with  ammoniacal  solution  of 
copper  till  decolorization  is  effected,  takes  too  much  time,  and  is 
apt  to  give  false  results  (PHILLIPS,  f  EKDMANN^;).  The  latter  remark 
applies  also  to  the  indirect  method  proposed  by  RUNGE,  which  con- 
sists in  boiling  the  solution  of  copper,  free  from  nitric  acid  and 
ferric  salts,  in  presence  of  some  free  hydrochloric  acid,  in  a  flask,, 
with  a  weighed  strip  of  copper,  and,  after  decolorization  of  the 
fluid,  determining  the  loss  of  weight  suffered  by  the  copper. 

1.  Determination  as  Oupric  Oxide. 

a.  By  direct  Precipitation  as  Oxide. 

Heat  the  rather  dilute  neutral  or  acid  solution  in  a  platinum  or 
porcelain  dish,  to  incipient  ebullition,  add  a  somewhat  dilute  solu- 
tion of  pure  soda  or  potassa  until  the  formation  of  a  precipitate 
ceases,  and  keep  the  mixture  a  few  minutes  longer  at  a  tempera- 
ture near  boiling.  Allow  to  subside,  filter,  wash  by  decantation 
twice  or  thrice,  boiling  up  each  time,  then  collect  it  on  the  filter,, 
wash  thoroughly  with  hot  water,  dry,  and  ignite  in  a  porcelain  or 
platinum  crucible,  as  directed  §53.  Do  not  use  the  blow-pipe- 
After  ignition,  and  having  added  the  ash  of  the  filter,  let  the 
crucible  cool  in  the  desiccator,  and  weigh.  The  action  of  reducing 
gases  must  be  carefully  guarded  against  in  the  process  of  ignition. 

It  will  sometimes  happen,  though  mostly  from  want  of  proper 
attention  to  the  directions  here  given,  that  particles  of  the  precipi- 

*  This  subject  hardly  comes  within  the  scope  of  the  present  work.  I  there- 
fore refer  to  AL.  MULLER,  das  Complemcntarcolorimeter,  Chemnitz,  1854;  Bo- 
DEMANN'S  Probirkunst  von  KERL,  222;  also  to  DEHMS,  Zeitschr.  f.  anal.  Chem. 
3,  218,  and  GUSTAV  BISCHOF,  jun.,  Ib.  6,  459. 

f  Annal.  d.  Chem.  u.  Pharm.  81,  208.        \  Jour.  f.  prakt.  Chem.  75,  211. 


§  119.]  COPPER.  313 

tate  adhere  so  tenaciously  to  the  dish  as  to  be  mechanically  irremov- 
able. In  a  case  of  this  kind,  after  washing  the  dish  thoroughly, 
dissolve  the  adhering  particles  with  a  few  drops  of  nitric  acid,  and 
evaporate  the  solution  over  the  principal  mass  of  the  precipitated 
oxide,  before  you  proceed  to  ignite  the  latter.  Should  the  solution 
be  rather  copious,  it  must  first  be  concentrated  by  evaporation, 
until  only  very  little  of  it  is  left.  For  the  properties  of  the  pre- 
cipitate, see  §  85. 

With  proper  attention  to  the  directions  here  given,  the  results 
obtained  by  this  method  are  quite  accurate,  otherwise  they  may  be 
either  too  high  or  too  low.  Thus,  if  the  solution  be  not  sufficiently 
dilute,  the  precipitant  will  fail  to  throw  down  the  whole  of  the 
copper ;  or  if  the  precipitate  be  not  thoroughly  washed  with  hot 
water,  it  will  retain  a  portion  of  the  alkali ;  or  if  the  ignited  pre- 
cipitate be  allowed  to  stand  exposed  to  the  air  before  it  is  weighed, 
an  increase  of  weight  will  be  the  result ;  and  so,  on  the  other  hand, 
a  diminution  of  weight,  if  the  oxide  be  ignited  with  the  filter  or 
under  the  influence  of  reducing  gases,  as  thereby  cuprous  oxide 
would  be  formed.  Should  a  portion  of  the  oxide  have  suffered 
reduction,  it  must  be  reoxidized  by  moistening  with  nitric  acid, 
evaporating  cautiously  to  dry  ness,  and  exposing  the  residue  to  a 
gentle  heat,  increasing  this  gradually  to  a  high  degree  of  intensity. 

Let  it  be  an  invariable  rule  to  test  the  filtrate  for  copper  with 
hydrogen  sulphide  water.  If ,  notwithstanding  the  strictest  compli- 
ance with  the  directions  here  given,  the  addition  of  this  reagent 
produces  a  precipitate,  or  imparts  a  brown  tint  to  the  fluid,  this  is 
to  be  attributed  to  the  presence  of  organic  matter ;  in  that  case, 
concentrate  the  filtrate  and  wash-water  by  evaporation,  acidify, 
precipitate  with  hydrogen  sulphide  water,  filter,  incinerate  the 
filter,  heat  with  nitric  acid,  dilute,  filter,  concentrate,  precipitate 
with  soda,  and  add  the  oxide  obtained  to  the  main  quantity. 

Never  neglect  to  test  the  cupric  oxide  after  weighing  for  alkali 
or  alkali  salt  by  boiling  it  with  water.  If  either  is  present,  the 
oxide  must  be  exhausted  with  hot  water,  and  then  reignited  and 
reweighed.  Finally,  dissolve  the  oxide  in  hydrochloric  acid  to 
detect  and  if  necessary  to  estimate  any  silicic  acid  it  may  contain. 

In  default  of  sufficiently  pure  potash  or  soda,  the  carbonate* 
may  be  used,  but  the  solution  must  not  contain  more  than  1  grin, 
copper  in  the  litre;  the  alkali  carbonate  must  only  be  added 
slightly  in  excess,  and  the  mixture  must  be  boiled  for  half  an  hour. 


314  I)  KT  V. K  M  I  .\  A  T  ION.  [§  1 1 9. 

The  bluish-green  precipitate  will  tlien  turn  dark  brown  and  gran- 
ular, and  may  be  easily  washed  (GIBBS*). 

From  ammoniacal  solutions,  also,  copper  may  be  precipitated 
l)y  soda  or  potassa.  In  the  main,  the  process  is  conducted  as  above. 
After  precipitation  the  mixture  is  heated,  until  the  supernatant 
fluid  has  become  perfectly  colorless ;  the  fluid  is  then  filtered  off 
with  the  greatest  possible  expedition.  If  allowed  to  cool  with  the 
precipitate  in  it,  a  small  portion  of  the  latter  would  redissolve. 

b.  By  Precipitation  ax   Oxide,  preceded  by   Ignition  of  the 
Substance. 

Heat  the  substance  in  a  porcelain  crucible,  until  the  organic 
matter  present  is  totally  destroyed ;  dissolve  the  residue  in  dilute 
nitric  acid,  filter  if  necessary,  and  treat  the  clear  solution  as 
directed  in  a. 

c.  By  Ignition. 

The  salt  is  put  into  a  platinum  or  porcelain  crucible,  and 
exposed  to  a  very  gentle  heat,  which  is  gradually  increased  to 
intense  redness;  the  residue  is  then  weighed.  As  cupric  nitrate 
spirts  strongly  when  ignited,  it  is  always  advisable  to  put  it  into  a 
small  covered  platinum  crucible,  and  to  place  the  latter  in  a  large 
one,  also  covered.  With  proper  care,  the  results  are  accurate 
Cupric  salts  of  organic  acids  may  also  be  con  verted  into  cupric  oxide 
by  simple  ignition.  To  this  end,  the  residue  iirst  obtained,  which 
contains  cuprous  oxide,  is  completely  oxidized  by  ignition  with 
mercuric  oxide  (which  leaves  no  residue  on  ignition),  or,  with  less 
advantage,  by  repeated  moistening  with  nitric  acid,  and  ignition. 
A  loss  of  substance  is  generally  incurred  by  the  use  of  nitric  acid 
from  the  difficulty  of  avoiding  spirting. 

2.  Determination  at*  Metallic  Copper, 
a.  By  Precipitation  with  Zinc  or  Cadmium.^ 
Introduce  the  solution  of  copper,  after  having,  if  required,  first 
freed  it  from  nitric  acid,  by  evaporation  with  hydrochloric  acid  or 

*  Zeitschr.  f.  anal.  Chem.  7,  258. 

f  The  method  of  precipitating  copper  by  iron  or  zinc,  and  weighing  it  in  the 
metallic  form,  was  proposed  long  ago ;  see  PFAFF'S  Handbuch  der  analytischen 
Chemie,  Altoua,  1822,  2,  269;  where  the  reasons  are  given  for  preferring  zinc  as 
a  precipitant,  and  hydrogen  sulphide  is  recommended  as  a  test  for  ascertaining 
whether  the  precipitation  is  complete.  I  mention  this  with  reference  to  F.  MOHR'S 
paper  in  the  Annal.  d.  Chem.  u.  Pharm.  96,  215,  and  BODEMANN'S  Probirkunst 
von  KERL,  220.' 


§  119.]  COPPER.  315 

sulphuric  acid,  into  a  weighed  platinum  dish ,  dilute,  if  necessary 
with  some  water,  throw  in  a  piece  of  zinc  (soluble  in  hydrochloric 
acid  without  residue),  and  add,  if  necessary,  hydrochloric  acid  in 
sufficient  quantity  to  produce  a  moderate  evolution  of  hydrogen. 
If,  on  the  other  hand,  this  evolution  should  be  too  brisk,  owing  to 
too  large  excess  of  acid,  add  a  little  water.  Cover  the  dish  with  a 
watch-glass,  which  is  afterwards  rinsed  into  the  dish  with  the  aid 
of  a  washing-bottle.  The  separation  of  the  copper  begins  imme- 
diately ;  a  large  proportion  of  it  is  deposited  on  the  platinum  in 
form  of  a  solid  coating;  another  portion  separates,  more  particu- 
larly from  concentrated  solutions,  in  the  form  of  red  spongy  masses. 
Application  of  heat,  though  it  promotes  the  reaction,  is  not  abso- 
lutely necessary ;  but  there  must  always  be  sufficient  free  acid 
present  to  keep  up  the  evolution  of  hydrogen.  After  the  lapse  of 
about  an  hour  or  two,  the  whole  of  the  copper  has  separated.  To 
make  sure  of  this,  test  a  small  portion  of  the  supernatant  fluid 
with  hydrogen  sulphide  water ;  if  this  fails  to  impart  a  brown  tint 
to  it,  you  may  safely  assume  that  the  precipitation  of  the  copper  is 
complete.  Ascertain  now,  also,  whether  the  zinc  is  entirely  dis- 
solved, by  feeling  about  for  any  hard  lumps  with  a  glass  rod,  and 
observing  whether  renewed  evolution  of  hydrogen  will  take  place 
upon  addition  of  some 'hydrochloric  acid.  If  the  results  are  satis- 
factory in  this  respect  also,  press  the  copper  together  with  the  glass 
rod,  decant  the  clear  fluid,  which  is  an  easy  operation,  pour,  with- 
out loss  of  time,  boiling  water  into  the  dish,  decant  again,  and 
repeat  this  operation  until  the  washings  are  quite  free  from  hydro- 
chloric acid.  Decant  the  water  now  as  far  as  practicable,  rinse  the 
dish  with  strong  alcohol,  dry  at  100°,  let  it  cool,  and  weigh.  If 
you  have  no  platinum  dish,  the  precipitation  may  be  effected  also 
in  a  porcelain  crucible  or  glass  dish ;  but  it  will,  in  that  case,  take 
a  longer  time ;  and  the  whole  of  the  copper  will  be  obtained  in 
loose  masses,  and  not  firmly  adhering  to  the  sides  of  the  crucible 
or  dish,  as  in  the  case  of  precipitation  in  platinum  vessels. 

The  results  are  very  accurate.  The  direct  experiment,  No. 
78,  gave  10OO  and  100-06,  instead  of  100.  FK.  MOHR  (loc.  cit.) 
obtained  equally  satisfactory  results  by  precipitating  in  a  porcelain 
crucible.* 


*  STOKER  (On  the  alloys  of  copper  and  zinc,  Cambridge,  1860,  p.  47)  says  that 
the  precipitated  copper  retains  water,  but  I  have  not  found  this  to  be  the  case. 


316  DKT.KKMINAT10N.  [§ 

Zinc  being  sometimes  difficult  to  obtain  of  sufficient  purity, 
cadmium  may  be  used  instead;  it  dissolves  with  less  violence  in 
strongly  acid  copper  solutions.  It  maybe  used  in  the  form  of  rod 
in  which  it  usually  occurs  in  commerce  (CLASSEN*). 

1).  I>y  Precipitation  with  tlte  Galvanic  Current. 

This  method  makes  us  independent  of  pure  zinc  or  cadmium, 
and  yields  the  copper  in  a  compact  form,  readily  washed  and  deter- 
mined. It  is  now  largely  used  in  copper  works,  constant  batteries 
have  been  employed  for  it,  and  the  whole  process  has  been  organ- 
ized for  use  on  a  large  scale  by  LUCKOW,  and  adopted  by  the  Mans- 
feld  Ober-Berg-und  Hut  ten-Direction  in  Eisleben.f  A  small  elec- 
trolytic apparatus  without  separate  battery,  for  single  precipitations,, 
has  been  described  by  ULLGKEN.J: 

c.  By  Ignition  in  Hydrogen. 

The  oxides  of  copper  when  ignited  in  a  current  of  pure  hydro- 
gen are  converted  into  metallic  copper,  and  may  thus  be  conven- 
iently analyzed.  Occasionally  the  cupric  oxide  obtained  by  1,  a  or 
b,  is  reduced  either  at  once,  or  after  weighing ;  in  the  latter  case 
the  reduction  serves  as  a  control. 

3.  Determination  as  Cuprous  Sulphide. 

a.  By  Precipitation  as  Cupric  Sulphide. 

Precipitate  the  solution — which  is  best  moderately  acid,  but 
should  not  contain  a  great  excess  of  nitric  acid — according  to  the 
quantity  of  copper  present,  either  by  the  addition  of  strong  hydro- 
gen sulphide  water, or  bypassing  the  gas.  In  the  absence  of  nitric 
acid  it  is  well  to  heat  nearly  to  boiling  while  the  gas  is  passing,  as 
this  makes  the  precipitate  denser,  and  it  is  more  easily  washed. 
When  the  precipitate  has  fully  subsided,  and  you  have  made  sure 
that  the  supernatant  fluid  is  no  longer  colored  or  precipitated  by 
strong  hydrogen  xulphide  water,  filter  quickly,  wasli  the  precipi- 
tate without  intermission  with  water  containing  hydrogen  sulphide, 
and  dry  on  the  filter  with  some  expedition.  Transfer  to  a  weighed 
porcelain  crucible,  add  the  filter-ash  and  some  pure  powdered  sul- 
phur, and  ignite  strongly  in  a  stream  of  hydrogen  (§  108,  fig.  50). 
It  is  advisable  to  use  a  glass  blow-pipe.  The  results  are  very  accu- 
rate (H.  EOSE§). 


*  Journ.  f.  prakt.  Chem.  96,  259. 

f  Zeitschr.  f.  anal.  Chem.  8,  23  and  11, 1.    Compare  also  GIBBS,  Ib.  3,  334,  and 
LECOQ  DE  BOISBAUDAN,  Ib.  7,  253.        t  /'>•  ?>  442.        §  Pogg.  Annal.  110,  138. 


§  119.  ]  COPPER.  317 

This  method,  which  was  recommended  by  BERZELIUS,  and  after- 
wards by  BRUNNER,  has  only  lately  received  a  very  practical  form, 
from  the  apparatus  introduced  by  H.  ROSE.  I  feel  great  pleasure 
in  recommending  it.  In  my  own  laboratory  it  is  in  frequent  use. 

o.  By  Precipitation  as  Cuprous  Sulphocyanate^  after  RIVOT.* 

The  solution  should  be  as  free  as  possible  from  nitric  acid  and 
free  chlorine,  and  should  contain  little  or  no  free  acid.  Add  sul- 
phurous or  hypophosphorous  acid  in  sufficient  quantity,  and  then 
solution  of  potassium  sulphocyanate  in  the  least  possible  excess. 
The  copper  precipitates  as  white  cuprous  sulphocyanate.  It  is 
filtered  after  standing  some  time,  washed  and  dried,  mixed  with 
sulphur,  ignited  in  hydrogen  in  the  apparatus  mentioned  in  #,  and 
this  ignition  with  sulphur  is  repeated  till  the  weight  is  constant. 
The  precipitate  may  also  be  collected  on  a  weighed  filter,  dried  at 
100°,  and  then  weighed.  The  experiment,  Xo.  80,  conducted  in 
the  latter  way,  gave  99'66  instead  of  100.  The  process  yields 
satisfactory  results,  but  they  are  always  inclined  to  be  a  little  too 
low,  as  the  cuprous  sulphocyanate  is  not  absolutely  insoluble.  The 
loss  is  larger  in  the  presence  of  much  free  acid. 

c.  Cuprous  and  cupric  oxide,  cupric  sulphate,  and  many  other 
salts  of  copper  (but  not  chloride,  bromide,  or  iodide)  may  be  directly 
converted  into  cuprous  sulphide,  by  mixing  with  sulphur  and 
igniting  in  hydrogen  as  in  a  (H.  ROSE,  loo.  rit.).  The  results  are 
thoroughly  satisfactory. 

4.    Volumetric  Methods. 

a.  DE  HAEN'S  METHOD.! 

I  recommend  this  method,  which  was  devised  in  my  own 
laboratory,  as  more  especially  applicable  in  cases  where  small 
quantities  of  copper  are  to  be  estimated  in  an  expeditious  way. 
The  method  is  based  upon  the  fact  that,  when  a  cupric  salt  in 
solution  is  mixed  with  potassium  iodide  in  excess,  cuprous  iodide 
and  free  iodine  are  formed,  the  latter  remaining  dissolved  in  the 
solution  of  potassium  iodide  :  CuSO4  +  2KI  =.  Cul  +  K2SO4  +  I. 
Now,  by  estimating  the  iodine  by  BUNSEN'S  method,  or  with  sodium 
thiosulphate  (§  146),  we  learn  the  quantity  of  copper,  as  1  at, 
iodine  (126-85)  corresponds  to  1  at.  copper  (63-4).  The  following 
is  the  most  convenient  way  of  proceeding:  Dissolve  the  compound 


*Compt.  Rend.  38,  868;  Journ.  f.  prakt.  Chem.  62,  252. 
f  Annal.  d.  Chem.  u.  Pharm.  91,  237. 


318  DETERMINATION.  |$12<). 

of  copper  in  sulphuric  acid,  best  to  a  neutral  solution  ;  a  moderate 
excess  of  free  sulphuric  acid,  however,  does  not  injuriously  affect 
the  process.  Dilute  the  solution,  in  a  measuring  flask,  to  a  defi- 
nite volume;  100  c.c.  should  contain  from  1  to  2  grin,  of  copper. 
Introduce  now  about  10  c.c.  of  potassium  iodide  solution  (1  in  10) 
into  a  stoppered  bottle,  add  10  c.c.  of  the  copper  solution,  mix, 
allow  to  stand  10  minutes,  and  then  determine  the  separated 
iodine,  either  with  sulphurous  acid  and  iodine  (§  146,  1),  or  with 
sodium  thiosulphate  (§  146,  2).  The  copper  solution  must  be  free 
from  ferric  salts  and  other  bodies  wrhich  decompose  potassium 
iodide,  also  free  nitric  acid,  and  free  hydrochloric  acid ;  and  the 
solution  must  not  be  allowed  to  stand  too  long  before  titration. 
With  strict  attention  to  these  rules,  the  results  are  accurate.  I)E 
HAEN  obtained,  for  instance,  "3567  instead  of  '3566  of  cupric  sul- 
phate, 99;89  and  lOO'l  instead  of  100  of  metallic  copper.  Further 
experiments  (No.  81)  have  convinced  me,  however,  that,  though 
the  results  attainable  by  this  method  are  satisfactory,  they  are  not 
always  quite  so  accurate  as  would  be  supposed  from  the  above 
figures  given  by  DE  HAEN.  Acting  upon  FR.  MOHK'S  suggestion, 
I  tried  to  counteract  the  injurious  influence  of  the  presence  of 
nitric  acid,  by  adding  to  the  solution  containing  nitric  acid,  first, 
ammonia  in  excess,  then  hydrochloric  acid  to  slight  excess;  the 
result  was  by  no  means  satisfactory.  The  reason  of  this  is  that  a 
solution  of  ammonium  nitrate,  mixed  with  some  hydrochloric  acid, 
will,  even  after  a  short  time,  begin  to  liberate  iodine  from  solution 
of  potassium  iodide. 

§120. 

6.  BISMUTH. 

a.  Solution. 

Metallic  bismuth,  bismuth  trioxide,  and  all  other  compounds  of 
that  metal,  are  dissolved  best  in  nitric  acid,  more  or  less  diluted. 
It  must  be  borne  in  mind  that  hydrochloric  acid  solutions  of 
bismuth,  if  concentrated,  cannot  be  evaporated  without  loss  of 
bismuth  chloride. 

~b.  Determination. 

Bismuth  is  weighed  in  the  form  of  trioxide,  of  chromate,  of 
sulphide,  or  in  the  metallic  state.  The  compounds  of  bismuth  are 
converted  into  trioxide  by  ignition,  by  precipitation  as  basic  car- 


£  120.]  BISMUTH.  319 

bonate,  or  by  repeated  evaporation  of  the  nitric  solution.     These 
are   sometimes  preceded  by  separation  as  sulphide.     The   deter- 
mination as  metallic  bismuth  is  frequently  preceded  by  precipita- 
tion as  sulphide  or  as  basic  chloride. 
We  may  convert  into 

1.  BISMUTH  TRIOXIDE: 

a.  By  Precipitation  as  basic  Bismuth  Carbonate.     All  com- 
pounds of  bismuth  which  dissolve  in  nitric  acid  to  nitrate,  no  other 
acid  remaining  in  the  solution. 

b.  By  Ignition. 

a.  Bismuth  salts  pf  readily  volatile  oxygen  acids. 
ft.  Bismuth  salts  of  organic  acids. 

c.  By  Evaporation.     Bismuth  in  nitric  acid  solution. 

d.  By  Precipitation  as  Bismuth  Trisulphide.    All  compounds 
of  bismuth  without  exception. 

2.  BISMUTH  CHROMATE.     All  compounds  named  in  1,  a. 

3.  BISMUTH  TRISULPHIDE.     The  compounds  *of  bismuth  without 
exception. 

4.  METALLIC    BISMUTH  :    The  trioxide  and  oxygen   salts,   the 
sulphide,  the  basic  chloride,  in  which  latter  form  the  bismuth  may 
be  precipitated  out  of  all  its  solutions. 

1.  Determination  of  Bismuth  as  Trioxide. 

a.  By  Precipitation  as  Bismuth  Carbonate. 

If  the  solution  is  concentrated  add  water,  taking  no  notice  of 
any  precipitate  of  basic  nitrate  that  may  be  formed.  Mix  with 
ammonium  carbonate  in  very  slight  excess,  and  heat  for  some  time 
nearly  to  boiling ;  filter,  dry  the  precipitate,  and  ignite  in  the  man- 
ner directed  §  116,  1  (Ignition  of  lead  carbonate) ;  the  process  of 
ignition  serves  to  convert  the  carbonate  into  bismuth  trioxide.  For 
the  properties  of  the  precipitate  and  residue,  see  §  86.  The  method 
gives  accurate  results,  though  generally  a  trifle  too  low,  owing  to 
the  circumstance  that  bismuth  carbonate  is  not  absolutely  insoluble 
in  ammonium  carbonate.  Were  you  to  attempt  to  precipitate 
bismuth,  by  means  of  ammonium  carbonate,  from  solutions  con- 
taining sulphuric  acid  or  hydrochloric  acid,  you  would  obtain 
incorrect  results,  since  with  the  basic  carbonate,  basic  sulphate  or 
basic  chloride  would  be  precipitated,  which  are  not  decomposed  by 
excess  of  ammonium  carbonate.  Were  you  to  filter  off  the  precipi- 
tate without  warming,  a  considerable  loss  would  be  sustained,  as 


320  DETERMINATION.  [§  120. 

the  whole  of  the  basic  carbonate  would  not  have  been  separated 
.(Expt.  No.  83). 

J.  By  Ignition. 

a.  Compounds  like  bismuth  carbonate  or  nitrate  are  ignited  in 
a  porcelain  crucible  until  their  weight  remains  constant. 

/?.  Salts  of  organic  acids  are  treated  like  the  corresponding 
compounds  of  copper  (§  119,  1,  c). 

c.  By  Evaporation. 

The  solution  of  the  nitrate  is  evaporated,  in  a  porcelain  dish  on 
the  water-bath,  till  the  neutral  salt  remains  in  syrupy  solution ; 
add  water,  loosen  the  white  crust  that  is  formed  with  a  glass  rod 
from  the  sides,  evaporate  again  on  a  water-bath,  reprecipitate  with 
water,  and  repeat  the  whole  operation  three  or  four  times.  After 
the  dry  mass  on  the  water-bath  has  ceased  to  smell  of  nitric  acid, 
it  is  allowed  to  cool  thoroughly,  and  then  treated  with  cold  water 
containing  a  little  ammonium  nitrate  (1  in  500) ;  after  the  residue 
and  fluid  have  been  a  short  time  together,  filter,  wash  with  the 
weak  solution  of  ammonium  nitrate,  dry  and  ignite  (§  53).  Results 
very  satisfactory  (J.  LOWE*). 

d.  By  Precipitation  as  Bismuth  Trisulphide. 

Dilute  the  solution  with  water  slightly  acidulated  with  acetic 
acid  (to  prevent  the  precipitation  of  a  basic  salt),  and  precipitate 
with  hydrogen  sulphide  water  or  gas ;  allow  the  precipitate  to 
subside,  and  test  a  portion  of  the  supernatant  fluid  with  hydrogen 
sulphide  water:  if  it  remains  clear,  which  is  a  sign  that  the 
bismuth  is  completely  precipitated,  filter  (the  filtrate  should  smell 
strongly  of  H3S),  and  wash  the  precipitate  with  water  containing 
hydrogen  sulphide.  Or  mix  with  ammonia  until  the  free  acid  is 
neutralized,  then  add  ammonium  sulphide  in  excess,  and  allow  to 
digest  for  some  time. 

The  washed  precipitate  may  now  be  weighed  in  three  different 
forms,  viz.,  as  trisulphide,  as  metal,  or  as  trioxide.  The  treatment 
in  the  two  former  cases  will  be  described  in  3  and  4 :  in  the  latter 
case  proceed  as  follows : 

Spread  the  filter  out  on  a  glass  plate  and  remove  the  precipitate 
to  a  vessel  by  means  of  a  jet  of  water  from  the  wash-bottle — or,  if 
this  is  not  practicable,  put  the  precipitate  and  filter  together  into 
the  vessel — and  heat  gently  with  moderately  strong  nitric  acid 

*  Journ.  f .  prakt.  Chem.  74,  344. 


§  120.]  BISMUTH.  321 

until,  complete  decomposition  is  effected ;  the  •  solution  is  then 
diluted  with  water  slightly  acidulated  with  acetic  or  nitric  acid, 
and  filtered,  the  filter  being  washed  with  the  acidulated  water;  the 
filtrate  is  then  finally  precipitated  as  directed  in  a. 

2.  Determination  of  Bismuth  as  Chromate  (J.  LOWE*). 
Pour  the  solution  of  bismuth,  which  must  be  as  neutral  as 

possible,  and  must,  if  necessary,  be  first  freed  from  the  excess  of 
nitric  acid  by  evaporation  on  the  water-bath,  into  a  warm  solution 
of  pure  potassium  dichromate  in  a  porcelain  dish,  with  stirring, 
and  take  care  to  leave  the  alkali  chromate  slightly  in  excess. 
Rinse  the  vessel  which  contained  the  solution  of  bismuth  with 
water  containing  nitric  acid  into  the  porcelain  dish.  The  precipi- 
tate formed  must  be  orange-yellow,  and  dense  throughout ;  if  it  is 
nocculent,  and  has  the  color  of  the  yolk  of  an  egg,  this  is  a  sign 
that  there  is  a  deficiency  of  potassium  dichromate ;  in  which  case 
add  a  fresh  quantity  of  this  salt,  taking  care,  however,  to  guard 
against  too  great  an  excess,  and  boil  until  the  precipitate  presents 
the  proper  appearance.  Boil  the  contents  of  the  dish  for  ten 
minutes,  with  stirring  ;  then  wash  the  precipitate,  first  by  repeated 
boiling  with  water  and  decantation  on  to  a  weighed  filter,  at  last 
thoroughly  on  the  latter  with  boiling  water ;  dry  at  about  120°, 
and  weigh.  For  the  properties  and  composition  of  the  precipitate, 
see  §  86.  Results  very  satisfactory. 

3.  Determination  of  Bismuth  as  Trisulphide. 
Precipitate  the  bismuth  as  trisulphide  according  to  1,  d.     I? 

the  precipitate  contains  free  sulphur,  extract  the  latter  by  boiling 
with  solution  of  sodium  sulphite,  or  by  treatment  with  carbon 
disulphide  (compare  the  determination  of  mercury  as  sulphide, 
§  118,  3),  collect  on  a  weighed  filter,  dry  at  100°,  and  weigh. 

The  drying  must  be  conducted  with  caution.  At  first  the 
precipitate  loses  weight,  by  the  evaporation  of  water,  then  it  gains 
weight,  from  the  absorption  of  oxygen.  Hence  you  should  weigh 
every  half  hour,  and  take  the  lowest  weight  as  the  correct  one. 
Compare  Expt.  No.  58.  Properties  and  composition,  §  86,  g. 

The  bismuth  sulphide  cannot  be  conveniently  converted  into 
the  metallic  state  by  ignition  in  hydrogen,  as  its  complete  decom- 
position is  a  work  of  considerable  time.  As  regards  reduction 
with  potassium  cyanide,  see  4. 

*  Journ.  f.  prakt.  Chem.  67,  464. 


322  DETERMINATION.  [§  120. 

4.  Determination  of  Bismuth  as  Metal. 

The  oxide,  sulphide,  or  basic  chloride  that  are  to  be  reduced 
are  fused  in  a  porcelain  crucible  with  five  times  their  quantity  of 
ordinary  potassium  cyanide.  The  crucible  must  be  large  enough. 
In  the  case  of  oxide  and  basic  chloride,  the  reduction  is  completed 
in  a  short  time  at  a  gentle  heat ;  sulphide,  on  the  other  hand, 
requires  longer  fusion  and  a  higher  temperature.  The  operation 
has  been  successful  if  on  treatment  with  water  metallic  grains  are 
obtained.  These  grains  are  first  washed  completely  and  rapidly 
with  water,  then  with  weak  and  lastly  with  strong  alcohol,  dried 
and  weighed.  If  you  have  been  reducing  the  sulphide,  and  on 
treating  the  fused  mass  with  water  a  black  powder  (a  mixture  of 
bismuth  with  bismuth  sulphide)  is  visible,  besides  the  metallic  grains, 
it  is  necessary  to  fuse  the  former  again  with  potassium  cyanide. 

It  sometimes  happens  that  the  crucible  is  attacked,  and  particles 
of  porcelain  are  found  mixed  with  the  metallic  bismuth  ;  to  prevent 
this  from  spoiling  the  analysis,  weigh  the  crucible  together  with  a 
small  dried  filter  before  the  experiment,  collect  the  rnetal  on  the 
filter,  dry  and  weigh  the  crucible  with  the  filter  and  bismuth  again. 
Kesults  good  (H.  ROSE*). 

The  precipitation  of  bismuth  as  basic  chloride,  and  the  reduc- 
tion of  the  latter  with  potassium  cyanide,  has  been  recommended 
by  II.  RosE.f  The  process  is  conducted  as  follows :  Nearly  neu- 
tralize any  large  excess  of  acid  that  may  be  present  with  potassa, 
soda,  or  ammonia,  add  ammonium  chloride  in  sufficient  quantity 
(if  hydrochloric  acid  is  not  already  present),  and  then  a  rather  large 
quantity  of  water.  After  allowing  to  stand  some  time,  test  whether 
a  portion  of  the  clear  supernatant  fluid  is  rendered  turbid  by  a 
further  addition  of  water ;  and  then,  if  required,  add  water  to  the 
whole  till  the  precipitation  is  complete.  Finally  filter,  wash  com- 
pletely with  cold  water,  dry  and  fuse  according  to  the  directions 
just  given  with  potassium  cyanide.  It  is  less  advisable  to  dry  the 
precipitate  at  100°,  weigh  and  calculate  the  metal  present  from  the 
formula  BiOCl,  as  washing  causes  a  slight  alteration  in  its  com- 
position (unless  a  little  hydrochloric  acid  is  added  to  the  wash- 
water,  which  is  inconvenient  when  the  precipitate  is  collected  on 
a  weighed  filter),  and  if  precipitated  in  the  presence  of  sulphuric, 
phosphoric  acids,  &c.,  it  is  liable  to  contain  small  quantities  of 
these  acids.  Results  accurate. 


*  Pogg.  Annal.  91,  104,  and  110,  136.  f  If).  110,  425. 


§  121.]  CADMIDM.  323 

§121. 

7.  CADMIUM. 

a.  Solution. 

Cadmium,  its  oxide,  and  all  the  other  compounds  insoluble  in 
water,  are  dissolved  in  hydrochloric  acid  or  in  nitric  acid. 

b.  Determination. 

Cadmium  is  weighed  either  in  the  form  of  oxide,  or  in  that  of 
sulphide  (§  87).  It  may  also  be  weighed  as  sulphate,  and  in  the 
absence  of  other  bases  precipitable  by  oxalic  acid,  it  may  be  esti- 
mated volumetrically. 

We  may  convert  into 

1.  CADMIUM  OXIDE: 

a.  By  Precipitation.  The  compounds  of  cadmium  which  are 
soluble  in  water ;  the  insoluble  compounds,  the  acid  of  which  is 
removed  upon  solution  in  hydrochloric  acid ;  cadmium  salts  of 
organic  acids. 

o.  By  Ignition.  Cadmium  salts  of  readily  volatile  or  easily 
decomposable  inorganic  oxygen  acids. 

2.  CADMIUM  SULPHDDE  :  All   compounds  of   cadmium  without 
exception. 

3.  CADMIUM  SULPHATE  :   All  compounds  of  cadmium,  in  the 
absence  of  other  non-volatile  substances. 

1.  Determination  as  Cadmium  Oxide. 

a.  By  Precipitation. 

Precipitate  with  potassium  carbonate,  wash  the  precipitated 
cadmium  carbonate,  and  convert  it,  by  ignition,  into  oxide.  The 
precipitation  is  conducted  as  in  the  case  of  zinc,  §  108,  1,  a.  The 
cadmium  oxide  which  adheres  to  the  filter  may  easily  be  reduced 
and  volatilized ;  it  is  therefore  necessary  to  be  cautious.  In  the 
first  place  choose  a  thin  filter,  transfer  the  dried  precipitate  as  com- 
pletely as  possible  to  the  crucible,  replace  the  filter  in  the  funnel, 
and  moisten  it  with  ammonium  nitrate  solution,  allow  to  dry,  and 
then  burn  carefully  in  a  coil  of  platinum  wire.  Let  the  ash  fall 
into  the  crucible  containing  the  mass  of  the  precipitate,  ignite 
carefully,  avoiding  the  action  of  reducing  gases,  and  finally  weigh. 
It  is  difficult  to  remove  the  last  portions  of  carbonic  acid  ;  you  must 
therefore  repeat  the  ignition  till  the  weight  remains  constant. 


324  DETERMINATION.  [§121. 

Properties  of  precipitate  and  residue,  §  87.      Results  generally  a 
little  too  low. 

Z>.   By  Ignition. 

Same  process  as  for  zinc,  §  108,  1,  c. 

2.  Determination  as  Cadmium  Sulphide. 

It  is  best  to  precipitate  the  moderately  acid  solution  with  hydro- 
gen sulphide  water  or  gas,  which  must  be  used  in  sufficient  excess. 
The  presence  of  a  considerable  quantity  of  free  hydrochloric  or 
nitric  acid  may — especially  if  the  solution  is  not  enough  diluted — 
prevent  complete  precipitation,  hence  such  an  excess  should  be 
avoided,  and  the  clear  supernatant  fluid  should  in  all  cases  be  tested, 
by  the  addition  of  a  relatively  large  amount  of  hydrogen  sulphide 
water  to  a  portion,  before  being  filtered.  Alkaline  solutions  of 
cadmium  may  be  precipitated  with  ammonium  sulphide.  If  the 
cadmium  sulphide  is  free  from  admixed  sulphur,  it  may  be  at  once 
collected  on  a  weighed  filter,  washed  first  with  diluted  hydrogen 
sulphide  water  mixed  with  a  little  hydrochloric  acid,  then  with 
pure  wrater,  dried  at  100°,  and  weighed ;  if,  on  the  contrary,  it  con- 
tains free  sulphur,  it  may  be  purified  by  boiling  with  a  solution  of 
sodium  sulphite,  or  by  treatment  with  carbon  di  sulphide  (see  Mer- 
curic Sulphide,  §  118,  3).  Results  accurate.  The  precipitation  of 
sulphur  may  occasionally  be  obviated  by  adding  to  the  cadmium 
;solution  potassium  cyanide  till  the  precipitate  first  formed  is  redis- 
solved,  and  then  precipitating  this  solution  with  hydrogen  sulphide. 

If  the  cadmium  sulphide  is  not  to  be  weighed  as  such,  warm  it, 
together  with  the  filter,  with  moderately  strong  hydrochloric  acid, 
till  the  precipitate  has  dissolved  and  the  odor  of  hydrogen  sulphide 
is  no  longer  perceptible,  filter  and  precipitate  the  solution  as  in 
1,  #,  after  having  removed  the  excess  of  free  acid  for  the  most  part 
by  evaporation. 

3.  Determination  as  Cadmium  Sulphate. 

Same  process  as  for  magnesium  (§  104,  1).  The  CdSO4  may 
be  rather  strongly  ignited  without  decomposition. 

4.  W.  GIBBS*  determines  cadmium  volumetrically  by  mixing 
the  concentrated  solution  of  the  sulphate,  nitrate,  or  chloride  with 
excess  of  oxalic  acid  and  a  quantity  of  strong  alcohol,  filtering, 
washing  with  alcohol,  dissolving  in  hot  hydrochloric  acid  and 

*Zeitschr.  f.  anal.  Chem.7,  259. 


§  122.]  PALLADIUM.  325 

determining  the  oxalic  acid  with  permanganate  (§  137).     "W.  G. 
LEISON*  obtained  satisfactory  results  by  this  process. 


Supplement  to  the  Fifth  Group. 

§122. 
8.  PALLADIUM. 

Palladium  is  converted,  for  the  purpose  of  estimation,  into  the 
metallic  state  •  or — in  many  separations — mto  potassium  palladia 
chloride. 

1.  Determination  a>-  Palladium. 

a.  Neutralize  the  solution  of  palladious  chloride  almost  com- 
pletely with  sodium   carbonate,  mix  with   solution   of  mercuric 
cyanide ;  and  heat  gently  for  some  time,  until  the  odor  of  hydro- 
cyanic acid  has  gone  off.    A  yellowish-white  precipitate  of  palladi- 
ous cyanide  will  subside  ;  from  dilute  solutions,  only  after  the  lapse 
of  some  time.     Wash  first  by  decantation,  then  on  the  filter,  dry 
thoroughly,  ignite  cautiously,  finally  over  the  gas  blowpipe  till  the 
palladium  paracyanide  first  formed  is  decomposed,  then  ignite  in 
hydrogen,  since  the  palladium  has  been  slightly  oxidized      As  soon 
as  the  lamp  is  removed,  stop  the  hydrogen  to  prevent  absorption, 
and  wreigh  the  metal.     If  the  solution  contains  palladious  nitrate, 
evaporate  it  first  with  hydrochloric  acid  to  dryness ;  as  otherwise 
the  precipitate  obtained  deflagrates  upon  ignition  (WOLLASTON). 
Results  exact. 

b.  Mix    the    solution    of   palladious   chloride    or   nitrate    with 
sodium  or  potassium  formate,  and  warm  until  no  more  carbonic 
acid  escapes.     The  palladium  precipitates  in  brilliant  scales  (DoBE- 
REINER). 

c.  Precipitate  the  acid  solution  of  palladium  with  hydrogen 
sulphide,  filter,  w^ash  with  boiling  water,  roast,  dissolve  in  hydro- 
chloric acid  and  nitric  acid,  and  precipitate  as  in  a. 

Exposed  to  a  moderate  red  heat  metallic  palladium  becomes 
covered  with  a  film  varying  from  violet  to  blue,  but  at  a  higher 
temperature  it  recovers  its  lustre,  which  it  keeps  after  being  sud- 
denly cooled,  for  instance,  with  cold  water.  This  tarnishing  and 
recovery  of  the  metallic  lustre  is  not  attended  with  any  percepti- 

*  Zeitschr.  f.  anal.  Chem.  10,  343. 


326  DETEKMINATION.  [§  123. 

ble  difference  of  weight.  Palladium  which  has  taken  up  oxygen 
is  immediately  reduced  in  hydrogen ;  when  cooled  in  the  current 
of  gas,  it  retains  some  absorbed  hydrogen.  Palladium  requires  the 
very  highest  degree  of  heat  for  its  fusion.  It  dissolves  readily  in 
nitrohydrochloric  acid,  with  difficulty  in  pure  nitric  acid,  more 
easily  in  nitric  acid  containing  nitrous  acid,  with  difficulty  in  boil- 
ing concentrated  sulphuric  acid. 

2.  Determination  as  Potassium  Palladic  Chloride. 

Evaporate  the  solution  of  palladic  chloride  with  potassium 
chloride  and  nitric  acid  to  dryness,  and  treat  the  mass  when  cold 
with  alcohol  of  '833  sp.  gr.,  in  which  the  double  salt  is  insoluble. 
Collect  on  a  weighed  filter,  dry  at  100°,  and  weigh.  Results  a 
little  too  low,  as  traces  of  the  double  salt  pass  away  with  the  alcohol 
washings  (BEEZELIUS).  Instead  of  weighing  the  double  salt  you 
may  ignite  in  hydrogen,  remove  the  potassium  chloride  with  water 
and  weigh  the  metal  obtained.  This  method  is  indeed  to  be  pre- 
ferred, as  it  prevents  any  potassiiim  chloride  in  the  precipitate  from 
affecting  the  result. 

POTASSIUM  PALLADIC  CHLORIDE  consists  of  microscopic  octa- 
hedra ;  it  presents  the  appearance  of  a  vermilion  or,  if  the  crystals 
are  somewhat  large,  of  a  brown  powrder.  It  is  very  slightly  solu- 
ble in  cold  water ;  it  is  almost  insoluble  in  cold  alcohol  of  the  above 
strength.  It  contains  26'806£  palladium. 

Sixth  Group. 

GOLD PLATINUM ANTIMONY TIN   IN    STANNIC   COMPOUNDS TIN     IN 

8TANNOUS     COMPOUNDS — ARSENIOUS     AND     AKSENIC     ACIDS (  MO- 

LYBDIC  ACID). 

§123. 

1.  GOLD. 

a.  Solution. 

Metallic  gold,  and  all  compounds  of  gold  insoluble  in  water, 
are  warmed  with  hydrochloric  acid,  and  nitric  acid  is  gradually 
added  until  complete  solution  is  effected ;  or  they  are  repeatedly 
digested  with  strong  chlorine  water.  The  latter  method  is  resorted 
to  more  especially  in  cases  where  the  quantity  of  gold  to  be  dis- 
solved is  small,  and  mixed  with  foreign  oxides  which  it  is  wished 


§123.].  GOLD.  327 

to  leave  undissolved.  According  to  W.  SKEY*  tincture  of  iodine, 
or,  for  larger  quantities  of  gold,  bromine  water,  is  better  than  chlo- 
rine water.  They  give  solutions  freer  from  other  metals  than  the 
chlorine  water  gives. 

b.  Determination. 

Gold  is  always  weighed  in  the  metallic  state.  The  compounds 
are  brought  into  this  form,  either  by  ignition  or  by  precipitation, 
as  gold,  or  auric  sulphide. 

We  convert  into 

METALLIC  GOLD  : 

a.  By  Ignition.    All  compounds  of  gold  which  contain  no  fixed 
acid,  or  other  body. 

b.  By  Precipitation  as  metallic  gold.     All  compounds  of  gold 
without  exception  in  cases  where  a  is  inapplicable. 

c.  By  Precipitation  as  auric  sulphide.     This  method  serves  to 
effect  the  separation  of  gold  from  certain  other  metals  which  may 
be  mixed  with  it  in  a  solution. 

Determination  as  Metallic  Gold. 

a.  By  Ignition. 

Heat  the  compound,  in  a  covered  porcelain  crucible,  very  gently 
at  first,  but  finally  to  redness,  and  weigh  the  residuary  pure  gold. 
For  properties  of  the  residue,  see  §  88.  The  results  are  most 
accurate. 

b.  By  Precipitation  as  Metallic  Gold. 

a.  The  solution  is  free  from  Nitric  Acid.  Mix  the  solution 
with  a  little  hydrochloric  acid,  if  it  does  not  already  contain  some 
of  that  acid  in  the  free  state,  and  add  a  clear  solution  of  ferrous 
sulphate  in  excess ;  heat  gently  for  a  few  hours  until  the  precipi- 
tated fine  gold  powder  has  completely  subsided ;  filter,  wash,  dry, 
and  ignite  according  to  §  52.  A  porcelain  dish  is  a  more  appro- 
priate vessel  to  effect  the  precipitation  in  than  a  beaker,  as  the 
heavy  fine  gold  powder  is  more  readily  rinsed  out  of  the  former- 
than  out  of  the  latter.  There  are  no  sources  of  error  inherent  in 
the  method. 

ft.  The  solution  of  Gold  contains  Nitric  Acid.  Evaporate  the 
solution,  on  a  water-bath,  to  the  consistence  of  syrup,  adding  from 
time  to  time  hydrochloric  acid ;  dissolve  the  residue  in  water  con- 

*  Zeitschr.  f.  anal.  Chem.  10,  221. 


328  DETERMINATION.  [§  123. 

taining  hydrochloric  acid,  and  treat  the  solution  as  directed  in  a. 
It  will  sometimes  happen  that  the  residue  does  not  dissolve  to  a 
clear  fluid,  in  consequence  of  a  partial  decomposition  of  auric  chlo- 
ride into  aurous  chloride  and  metallic  gold ;  however,  this  is  a  mat- 
ter of  perfect  indifference. 

y.  In  cases  where  it  is  wished  to  avoid  the  presence  of  iron  in 
the  filtrate,  the  gold  may  be  reduced  by  means  of  oxalic  acid.  To 
this  end,  the  dilute  solution — freed  previously,  if  necessary,  from 
nitric  acid,  in  the  manner  directed  in  ft — is  mixed,  in  a  beaker, 
with  oxalic  acid,  or  with  ammonium  oxalate  in  excess,,  some  sul- 
phuric acid  added  (if  that  acid  is  not  already  present  in  the  free 
state),  and  the  vessel,  covered  with  a  glass  plate,  is  kept  standing- 
for  two  days  in  a  moderately  warm  place.  At  the  end  of  that 
time,  the  whole  of  the  gold  will  be  found  to  have  separated  in 
small  yellow  scales,  which  are  collected  on  a  filter,,  washed  first 
with  dilute  hydrochloric  acid,  then  with  water,  dried,  and  ignited.. 
If  the  gold  solution  contains  a  large  excess  of  hydrochloric  acidr 
the  latter  should  be  for  the  most  part  evaporated,  before  the  solu- 
tion is  diluted  and  the  oxalic  acid  added.  If  the  gold  solution  con- 
tains chlorides  of  alkali  metals,  it  is  necessary  to  dilute  largely,  and 
allow  to  stand  for  a  long  time,  in  order  to  effect  complete  precipi- 
tation (H.  ROSE). 

&.  The  gold  may  also  be  thrown  down  in  the  metallic  form  by 
hydrate  of  chloral*  in  the  presence  of  potash.  Warm  the  solution, 
add  the  chloral,  then  pure  potash  in  excess,  and  boil  for  a  minute 
or  so.  The  gold  is  precipitated  with  evolution  of  chloroform. 

£.  Finally,  gold  may  be  thrown  down  by  many  metals,  such  as 
zinc,  cadmium,  magnesium,  &c.  The  latter  has  been  recommended 
by  ScHEiBLERf  for  the  analysis  of  the  gold  salts  of  organic  bases. 
The  precipitate  is  first  washed  with  hydrochloric  acid,  then  with 
water. 

c.  By  Precipitation  as  Auric  Sulphide. 

Hydrogen  sulphide  gas  is  transmitted  in  excess  through  the 
dilute  solution  containing  some  free  acid;  the  precipitate  formed 
is  speedily  filtered  off,  without  heating,  washed,  dried,  and  ignited 
in  a  porcelain  crucible.  For  the  properties  of  the  precipitate,  see 
§  88.  No  sources  of  error. 


*  HAGEH'S  pharmac.  Centralhalle,  11,  393. 
f  Ber.  der  dcutscli.  chem.  Gescllsch.  1869,  295. 


§  124.]  PLATINUM.  329 

i 

§124. 

2.  PLATINUM. 

a.  Solution. 

Metallic  platinum,  and  the  compounds  of  platinum  which  are 
insoluble  in  water,  are  dissolved  by  digestion,  at  a  gentle  heat,  with 
nitrohydrochloric  acid. 

b.  Determination. 

Platinum  is  invariably  weighed  in  the  metallic  state,  to  which 
condition  its  compounds  are  brought,  either  by  precipitation  aa 
ammonium  platinic  chloride,  potassium  platinic  chloride,  or  pla- 
tinic  sulphide,  or  by  ignition,  or  by  precipitation  with  reducing^ 
agents.  All  compounds  of  platinum,  without  exception,  may,  in 
most  cases,  be  converted  into  platinum  by  either  of  these  methods. 
Which  is  the  most  advantageous  process  to  be  pursued  in  special 
instances,  depends  entirely  upon  the  circumstances.  The  reduc- 
tion to  the1  metallic  state  by  simple  ignition  is  preferable  to  the 
other  methods,  in  all  cases  where  admissible.  The  precipitation  as 
platinic  sulphide  is  resorted  to  exclusively  to  eifect  the  separation 
of  platinum  from  other  metals. 

Determination  as  Metallic  Platinum. 

a.  By  Precipitation  as  Ammonium  Platinic  Chloride. 

The  solution  must  be  concentrated  if  necessary  by  evaporation 
on  a  water-bath.  Mix,  in  a  beaker,  with  ammonia  until  the  excess 
of  acid  (that  is,  supposing  an  excess  of  acid  to  be  present)  is  nearly 
saturated;  add  ammonium  chloride  in  excess,  and  mix  the  fluid 
with  a  pretty  large  quantity  of  strong  alcohol.  Cover  the  beaker 
now  with  a  glass  plate,  and  let  it  stand  for  twenty-four  hours,  after 
which  filter,  wash  the  precipitate  with  alcohol  of  about  '80  per 
cent.,  till  the  substances  to  be  separated  are  removed,  dry  carefully, 
ignite  according  to  §  99,  2,  and  weigh.  In  the  case  of  large  quan- 
tities the  final  ignition  is  advantageously  conducted  in  a  stream  of 
hydrogen  (§  108,  fig.  50),  in, order  to  be  quite  sure  of  effecting 
complete  decomposition.  For  the  properties  of  the  precipitate  and 
residue,  see  §  89.  The  results  are  satisfactory,  though  generally  a 
little  too  low,  as  the  ammonium  platinic  chloride  is  not  altogether 
insoluble  in  alcohol  of  the  above  strength  (Expt.  No.  16),  and  as 
the  fumes  of  ammonium  chloride  are  liable  to  carry  away  traces  of 


330  DETERMINATION.  [§  124. 

the  jet  nndecomposed  double  chloride,  if  the  application  of  heat  is 
not  conducted  with  the  greatest  care. 

If  the  precipitated  ammonium  platinic  chloride  were  weighed 
in  that  form,  the  results  would  be  inaccurate,  since,  as  I  have  con- 
vinced myself  by  direct  experiments,  it  is  impossible  to  completely 
free  the  double  chloride,  by  washing  with  alcohol,  from  all  traces 
of  the  ammonium  chloride  thrown  down  with  it,  without  dissolving 
at  the  same  time  a  notable  portion  of  the  double  chloride.  As  a 
general  rule,  the  results  obtained  by  weighing  the  ammonium  pla- 
tinic chloride  in  that  form  are  one  or  two  per  cent,  too  high. 

b.  By  Precipitation  as  Potassium  Platinic  Chloride. 

Mix  the  solution,  in  a  beaker,  with  potassa,  until  the  greater 
part  of  the  excess  of  acid  (if  there  be  any)  is  neutralized ;  add 
potassium  chloride  slightly  in  excess,  and  finally  a  pretty  large 
quantity  of  strong  alcohol ;  should  your  solution  of  platinum  be 
very  dilute,  you  must  concentrate  it  previously  to  the  addition  of 
the  alcohol.  After  twenty-four  hours,  collect  the  precipitate  upon 
n  rather  small  unweighed  filter,  wash  with  alcohol  of  80  per  cent., 
dry  thoroughly  at  100°,  and  transfer  to  a  porcelain  crucible,  dis- 
solving the  portion  which  adheres  to  the  filter,  and  evaporating  the 
solution  in  the  crucible.  See  §  97,  3.  Next,  by  igniting  with 
hydrogen  by  means  of  apparatus  described  in  §  108,  page  251,  con- 
vert the  compound  into  metallic  platinum  and  potassium  chloride. 
Reduction  is  best  effected  if  the  heat  is  very  gradually  applied,  and 
does  not  at  all  quite  reach  the  point  at  which  potassium  <;hloride 
fuses.  After  reduction,  wash  out  the  potassium  chloride,  ignite 
•and  weigh  the  platinum.  For  the  properties  of  the  precipitate 
:and  residue,  see  §  89. 

The  results  are  more  accurate  than  those  obtained  by  method  &, 
since,  on  the  one  hand,  the  potassium  platinic  chloride  is  more 
insoluble  in  alcohol  than  the  corresponding  ammonium  salt ;  and, 
on  the  other  hand,  loss  of  substance  is  less  likely  to  occur  during 
ignition.  To  weigh  the  potassium  platinic  chloride  in  that  form 
would  not  be  practicable,  as  it  is  impossible  to  remove,  by  washing 
with  alcohol,  all  traces  of  the  potassium  chloride  thrown  down 
with  it,  without,  at  the  same  time,  dissolving  a  portion  of  the 
double  chloride. 

c.  By  Precipitation  as  Platinic  Sulphide. 

Precipitate  the  solution  with  hydrogen  sulphide  water  or  gas, 


§  125.]  ANTIMONY.  331 

according  to  circumstances,  heat  the  mixture  to  incipient  ebulli- 
tion, filter,  wash  the  precipitate,  dry,  and  ignite  according  to  §  52. 
For  the  properties  of  the  precipitate  and  residue,  see  §  89.  The 
results  are  accurate. 

d.  By  Ignition. 

Same  process  as  for  gold,  §  123.  For  the  properties  of  the 
residue,  see  §  89.  The  results  are  most  accurate. 

e.  By  Precipitation  with  Reducing  Agents. 

Various  reducing  agents  may  be  employed  to  precipitate  plati- 
num from  its  solutions  in  the  metallic  state.  The  reduction  is 
very  promptly  effected  by  ferrous  sulphate  and  potassa  or  soda 
(the  protosesquioxide  of  iron  being  removed  by  subsequent  addi- 
tion of  hydrochloric  acid,  HEMPEL),  or  by  pure  zinc  or  magnesium 
(the  excess  of  which  is  removed  by  hydrochloric  acid) ;  somewhat 
more  slowly,  and  only  with  application  of  heat,  by  alkali  formiates. 
Mercurous  nitrate  also  precipitates  the  whole  of  the  platinum  from 
solution  of  platinic  chloride ;  upon  igniting  the  brown  precipitate 
obtained,  fumes  of  inercurous  chloride  escape,  and  metallic  plati- 
num remains. 

§125. 

3.  ANTIMONY. 

a.  Solution. 

Antimonious  oxide,  and  the  compounds  of  antimony  which  are 
insoluble  in  water,  or  are  decomposed  by  that  agent,  are  dissolved 
in  more  or  less  concentrated  hydrochloric  acid.  Metallic  antimony 
is  dissolved  best  in  nitrohydrochloric  acid.  The  ebullition  of  a 
hydrochloric  acid  solution  of  antimonious  chloride  is  attended  with 
volatilization  of  traces  of  the  latter ;  the  concentration  of  a  solution 
of  the  kind  by  evaporation  involves  accordingly  loss  of  substance. 
Solutions  so  highly  dilute  as  to  necessitate  a  recourse  to  evapora- 
tion must  therefore  previously  be  supersaturated  with  potassa. 
Solutions  of  antimonious  chloride,  which  it  is  intended  to  dilute 
with  water,  must  previously  be  mixed  with  tartaric  acid,  to  prevent 
the  separation  of  basic  salt.  In  diluting  an  acid  solution  of  anti- 
monic  acid  in  hydrochloric  acid,  the  water  must  not  be  added 
gradually  and  in  small  quantities  at  a  time,  which  would  make  the 
fluid  turbid,  but  in  sufficient  quantity  at  once,  which  will  leave  the 
fluid  clear. 


332  DETERMINATION.  [§ 

h.  Determination . 

Antimony  may  be  weighed  as  antmioiiious  sulphide 
tetrod'Ule,  \\\  separations  it  is  sometimes  weighed  as  metallic  anti- 
mony ,•  or  it  is  estimated  volumetrically. 

Antimony  in  solution  is  almost  invariably  first  precipitated  as 
sulphide,  which  is  then,  with  the  view  of  estimation,  converted 
into  anhydrous  sulphide,  or  determined  volnmetrically. 

1.  Precipitation  a*  Antiinon.iou#  Sulphide. 

Add  to  the  antimony  solution  hydrochloric  acid,  if  not  already 
present,  then  tartaric  acid,  and  dilute  with  water,  if  necessary. 
Introduce  the  clear  fluid  into  a  flask,  closed  with  a  doubly  perfo- 
rated cork ;  through  one  of  the  perforations  passes  a  tubey  bent 
outside  at  a  right  angle,  which  nearly  extends  to  the  bottom  of  the 
flask ;  through  the  other  perf oration  passes  another  tube,  bent  out- 
side twice  at  right  angles,  which  reaches  only  a  short  way  into  the 
flask ;  the  outer  end  of  this  tube  dips  slightly  under  water.  Con- 
duct through  the  first  tube  hydrogen  sulphide  gas,  until  it  pre- 
dominates strongly;  put  the  flask  in  a  moderately  warm  place,  and 
after  some  time  conduct  carbon  dioxide  into  the  fluid,  until  the 
excess  of  the  other  gas  is  almost  completely  removed.  If  there  is 
no  reason  against  it,  from  the  presence  of  a  large  quantity  of 
hydrochloric  acid,  or  from  the  presence  of  nitric  acid,  it  is  well  to- 
heat  the  solution  during  the  passing  of  the  gas,  finally  even  boiling. 
The  precipitate  is  then  denser,  and  may  be  very  easily  washed 
(SHARPLES*). 

If  the  amount  of  the  preet/pitate  •/*  <//  all  considerable,  filter 
without  intermission  through  a  weighed  filter,  wash  rapidly  and 
thoroughly  with  water  mixed  with  a  few  drops  of  hydrogen  sul- 
phide water,  dry  at  100°,  and  weigh.  The  precipitate  so  weighed 
always  retains  some  water,  and  may,  besides,  contain  free  sulphur; 
in  fact,  it  always  contains  the  latter  in  cases  where  the  antimony 
solution,  besides  aiitimonious  salts,  contains  antimonic  acid  or 
pentachloride  of  antimony,  since  the  precipitation  under  these 
circumstances  is  preceded  by  a  reduction  of  antimonic  to  antimo- 
nious  compounds,  accompanied  by  separation  of  sulphur  (II.  ROSE). 
A  further  examination  of  the  precipitate  is  accordingly  indispensa- 
ble. To  this  end,  treat  a  sample  of  the  weighed  precipitate  with 
strong  hydrochloric  acid.  If 


*  Zeitschr.  f.  anal.  Chem.  10,  343. 


§125.]  ANTIMONY.  333 

a.  The  sample  dissolves  to  ^  clear  fluid,  this  is  a  proof  that  the 
precipitate  only  contains  Sb2S3 ;  but  if 

&.  Sulphur  separates,  this  shows  that  free  sulphur  is  present. 

In  case  a  (in  order  to  remove  the  water  retained  at  100°)  the 
greater  portion  of  the  dried  precipitate  is  weighed  in  a  porcelain 
boat,  which  is  then  inserted  into  a  glass  tube,  about  2  decimetres 
long ;  a  slow  current  of  dry  carbon  dioxide  is  transmitted  through 
the  latter,  and  the  boat  cautiously  heated  by  means  of  a  lamp, 
moved  to  and  fro  under  it,  until  the  orange  precipitate  becomes 
Mack.  The  precipitate  is  then  allowed  to  cool  in  the  current  of 
carbon  dioxide,  and  weighed ;  from  the  amount  found,  the  total 
quantity  of  anhydrous  antimonious  sulphide  contained  in  the  entire 
precipitate  is  ascertained  by  a  simple  calculation.  The  results  arc 
accurate.  Expt.  Xo.  84  gave  99-22  instead  of  100.  But  if  the 
precipitate  is  simply  dried  at  100°,  the  results  are  about  2  per 
cent,  too  high — see  the  same  experiment.  For  the  properties  of 
the  precipitate,  sec  ;$  90. 

In  case  Z>,  the  precipitate  is  subjected  to  the  same  treatment  as 
in  <z,  with  this  difference  only,  that  the  -contents  of  the  boat  are 
heated  much  more  intensely,  and  the  process  is  continued  until  no 
more  sulphur  is  expelled.  This  removes  the  whole  of  the  admixed 
sulphur;  the  residue  consists  of  pure  antimonious  sulphide.  It 
must  be  completely  soluble  in  fuming  hydrochloric  acid  on  heating. 

If  tl«'  iininiinf  of  ike  precipitate  /'*  *///^//,  collect  it  in  a  weighed 
asbestos  filtering  tube,  dry  in  a  slow  current  of  carbon  dioxide  at  a 
gentle  heat,  heat  finally  rather  more  strongly  till  the  sulphide  has 
turned  black  and  any.  free  sulphur  present  has  volatilized,  allow  to 
cool,  replace  the  gas  in  the  tube  by  air,  and  weigh.  Results  quite 
satisfactory.-' 

For  the  method  of  estimating  the  antimony  in  the  sulphide 
volumetrically  and  indirectly,  see  3. 

2.  Determination  as  Antimony  Tetromde. 
a.  In  the  case  of  antimonious  oxide  or  a  compound  of  the 
same  with  an  easily  volatile  or  decomposable  oxygen  acid,  evapo- 
rate carefully  with  nitric  acid,  and  ignite  finally  for  some  time  till 
the  weight  is  constant.  The  experiment  may  be  safely  made  in  a 
platinum  crucible.  With  antimonic  acid,  the  evaporation  with 
nitric  acid  is  unnecessary. 

*  Zeitschr.  f .  anal.  Chem.  8, 155.  . 


334  DETERMINATION.  [§  125. 

b.  If  antimonious  sulphide  is  to  be  converted  into  antimony 
tetroxide,  one  of  the  two  following  methods  given  by  BUNSEN*  is 
employed : 

a.  Moisten  the  dry  sulphide  of  antimony  with  a  few  drops  of 
nitric  acid  of  1*42  sp.  gr.,  then  treat,  in  a  weighed  porcelain 
crucible,  with  concave  lid,  with  8 — 10  times  the  quantity  of 
fuming  nitric  acid,f  and  let  the  acid  gradually  evaporate  on  the 
water-bath.  The  sulphur  separates  at  first  as  a  fine  powder,  which, 
however,  is  readily  and  completely  oxidized  during  the  process  of 
evaporation.  The  white  residual  mass  in  the  crucible  consists  of 
antimonic  acid  and  sulphuric  acid,  and  may  by  ignition  be  con- 
verted, without  loss,  into  antimony  tetroxide.  If  the  sulphide  of 
antimony  contains  a  large  excess  of  free  sulphur,  this  must  be 
removed  by  washing  with  bisulphide  of  carbon. 

ft.  Mix  the  sulphide  of  antimony  with  30 — 50  times  its  quantity 
of  pure  mercuric  oxide, ^  and  heat  the  mixture  gradually  in  an 
open  porcelain  crucible.  As  soon  as  oxidation  begins,  which  may 
be  known  by  the  sudden  evolution  of  gray  mercurial  fumes, 
moderate  the  heat.  When  the  evolution  of  mercurial  fumes 
diminishes  raise  the  temperature  again,  always  taking  care,  how- 
ever, that  no  reducing  gases  come  in  contact  with  the  contents  of 
the  crucible.  Remove  the  last  traces  of  mercuric  oxide  over  the 
blast  gas-lamp,  then  weigh  the  residual  fine  white  powder  of  anti- 
mony tetroxide.  As  mercuric  oxide  generally  leaves  a  trifling  fixed 
residue  upon  ignition,  the  amount  of  this  should  be  determined 
once  for  all,  the  mercuric  oxide  added  approximately  weighed,  and 
the  corresponding  amount  of  fixed  residue  deducted  from  the 
antimony  tetroxide.  The  volatilization  of  the  oxide  of  mercury 
proceeds  much  more  rapidly  when  effected  in  a  platinum  crucible 
instead  of  a  porcelain  one.  But,  if  a  platinum  crucible  is  employed, 
it  must  be  effectively  protected  from  the  action  of  antimony  upon 
it,  by  a  good  lining  of  mercuric  oxide.§  If  the  sulphide  of  anti- 

*  Annal.  d.  Chem.  u.  Pharm.  106,  3. 

f  Nitric  acid  of  1'42  sp.  gr.  is  not  suitable  for  this  purpose,  as  its  boiling  point 
is  almost  10°  above  the  fusing  point  of  sulphur,  whereas  fuming  nitric  acid  boils 
at  86°,  consequently  below  the  fusing  point  of  sulphur.  With  nitric  acid  of  1  '42 
sp.  gr.,  therefore,  the  separated  sulphur  fuses  and  forms  drops,  which  obstinately 
resist  oxidation. 

\  Prepared  by  precipitation  from  mercuric  chloride  by  excess  of  soda  solution 
and  thorough  washing. 

§  This  is  effected  best,  according  to  BUN&EN,  in  the  following  way :  Soften  the 


§  125.]  ANTIMONY.  335 

mony  contains  free  sulphur,  this  must  first  be  removed  by  washing 
with  bisulphide  of  carbon,  before  the  oxidation  can  be  proceeded 
with,  since  otherwise  a  slight  deflagration  is  unavoidable. 

According  to  later  experiments  made  by  BUNSEN,*  it  is  some- 
what difficult  to  obtain  good  results  by  this  method,  because  a 
temperature  a  little  above  that  required  to  reduce  SbQO5  to  Sb2O4 
will  reduce  the  latter  SbaO3.  Ignition  over  a  blast-lamp  in  a  very 
large  covered  platinum,  or  rather  large  open  porcelain  crucible,  keep- 
ing only  the  bottom  at  a  full  red  heat,  is  recommended  as  a  method 
by  which  it  is  possible  to  drive  off  just  one  atom  O  from  Sb,O5. 

3.  Volumetric  Methods. 

a.  Conversion  of  Antimonious  Chloride  to  Antimonic  Chlo- 
ride by  Hydrochloric  Acid  and  Potassium  Chromate  ot*  Perman- 
yanate. 

~F.  KEssLEu'sf  first  description  of  this  method  was  so  wanting 
in  precision,  that  it  could  not  be  depended  upon..  However,  he 
has  since:}:  determined  most* accurately  the  conditions  under  which 
antimony  in  acid  solution  may  be  satisfactorily  titrated  either  with 
potassium  chromate  (the  excess  of  the  standard  solution  being 
determined  with  ferrous  sulphate)  or  with  potassium  permanganate. 

I.   Titration  with  Potassium  Dichromate. 
1.  REQUISITES. 

of.  Standard  Solution  of  Arsenious  Acid.  Dissolve  exactly 
5  grin,  pure  arsenious  oxide  by  the  aid  of  some  soda  solution,  add 
hydrochloric  acicl  till  slightly  acid,  then  100  c.c.  more  of  hydro- 
chloric acid  of  1'12  sp.  gr.,  and  dilute  to  1000  c.c.  Each  c.c.  con- 
tains *005  grm.  arsenious  oxide  and  corresponds  to  '007374  antiino- 
nious  oxide. 


sealed  end  of  a  common  test-tube  before  the  glass-blower's  lamp  ;  place  the 
softened  end  in  the  centre  of  the  platinum  crucible,  and  blow  into  it,  which  will 
cause  it  to  expand  and  assume  the  exact  form  of  the  interior  of  the  crucible. 
Crack  off  the  bottom  of  the  little  flask  so  formed,  and  smooth  the  sharp  edges 
cautiously  by  fusion.  A  glass  is  thus  obtained,  open  at  both  ends,  which  exactly 
fits  the  crucible.  To  effect  the  lining  by  means  of  this  instrument,  fill  the  crucible 
loosely  with  mercuric  oxide  up  to  the  brim,  then  force  the  glass  gradually  and 
slowly  down  to  the  bottom  of  the  crucible,  occasionally  shaking  out  the  oxide 
of  mercury  from  the  interior  of  the  glass.  The  inside  of  the  crucible  is  thus 
covered  with  a  layer  of  oxide  of  mercury  \ — 1  line  thick,  which,  after  the  removal 
of  the  glass,  adheres  with  sufficient  firmness,  even  upon  ignition. 

*  Zeitschr.  f.  anal.  Chem.  18,  268.  f  Pogg.  Annal.  95,  204. 

\  /'>.  118,  17;  and  Zeitschr.  f.  anal.  Chem.  2,  383. 


336  DETERMINATION.  [§  125. 

ft.  Solution  of  Potassium  Bichromate.  Dissolve  about  2*5  grm. 
to  1  litre. 

y.  Solution  of  Ferrous  Sulphate.  Dissolve  about  1/1  grm.  iron 
wire  in  20  c.c.  dilute  sulphuric  acid  (1  to  4),  filter,  and  dilute  to 
1  litre. 

8.  Solution  of  Potassium  Ferricyanide.  Should  be  tolerably 
dilute  and  freshly  prepared. 

2.  DETERMINATION  OF  THE  SOLUTIONS. 

af  Relation  betioeen  the  Solution  of  Chr ornate  and  the  Solution 
of  Ferrous  Sulphate.  Run  into  a  beaker  10  c.c.  of  the  chromate 
solution  from  the  burette,  add  5  c.c.  of  hydrochloric  acid  and  50 
c.c.  water,  and  then  add  iron  solution  from  a  burette  till  the  fluid 
is  green.  Continue  adding  the  iron  solution,  a  c.c.  at  a  time,  test- 
ting  after  each  addition  whether  a  drop  of  the  fluid,  when  brought 
in  contact  with  a  drop  of  the  potassium  ferricyanide,  on  a  porcelain 
plate,  manifesjts  a  distinct  reaction  for  ferrous  iron.  As  soon  as 
this  point  is  attained,  add  *5  c.c.  of  chromate  solution  and  then  iron 
solution  two  drops  at  a  time,  till  the  blue  reaction  just  occurs. 
Now  read  off  both  burettes,  and  calculate  how  much  chromate 
solution  corresponds  to  10  c.c.  of  iron  solution.  This  experiment 
is  to  be  repeated  before  every  fresh  series  of  analyses,  as  the  iron 
solution  gradually  oxidizes. 

/?.  Relation  between  the  Chromate  Solution  and  the  Solution  of 
Arsenious  Acid.  Transfer  10  c.c.  of  the  arsenious  solution  to  a 
beaker,  add  20  c.c.  hydrochloric  acid  of  1*2  sp.  gr.,  and  80 — 100 
c.c.*  water,  run  in  chromate  solution  till  the  yellow  color  of  the 
fluid  shows  an  excess,  wait  a  few  minutes,  add  excess  of  iron  solu- 
tion, then  again  '5  chromate  solution,  and  finally  again  iron  solu- 
tion till  the  end-reaction  appears  (see  above).  Deduct  from  the 
total  quantity  of  chromate  solution  employed,  the  amount  corre- 
sponding to  the  iron  used,  and  from  the  datum  thus  afforded  calcu- 
late how  much  antimony  corresponds  to  100  c.c.  of  chromate  solu- 
tion ;  in  other  words,  how  much  antimony  is  converted  by  the 
quantity  of  chromate  mentioned  from  SbCl3  into  SbCl6. 

3.  THE  ACTUAL  ANALYSIS. 

In  the  absence  of  organic  matter,  heavy  metallic  oxides,  and  other 

*  The  water  must  he  measured,  for  the  action  of  chromic  acid  on  arsenions 
acid  (and  also  on  antimonious  chloride)  is  normal  only  if  the  fluid  contains  at 
least  one  sixth  of  its  volume  of  hydrochloric  acid  of  1  '12  sp.  gr. 


§  125.]  ANTIMONY.  337 

bodies  which  are  detrimental  to  the  reaction,  dissolve  the  antimo- 
nious  compound  at  once  in  hydrochloric  acid.  The  solution  should 
contain  not  less  than  |  of  its  volume  of  hydrochloric  acid  of  1-12 
sp.  gr.  It  is  not  advisable,  on  the  other  hand,  that  it  should  con- 
tain more  than  ^,  otherwise  the  end-reaction  with  potassium  ferri- 
cyanide  is  slower  in  making  its  appearance  and  loses  its  nicety. 
Tartaric  acid  cannot  be  employed  as  a  solvent,  since  it  interferes 
with  the  action  of  chromic  acid  on  ferrous  salts.  Now  proceed  as 
directed  in  2.  If  the  direct  determination  of  antimony  in  the 
hydrochloric  acid  solution  is  not  practicable,  precipitate  it  with 
hydrogen  sulphide.  Wash  the  precipitate,  transfer  it,  together 
with  the  filter,  to  a  small  flask  ;  treat  it  with  a  sufficiency  of  hydro- 
chloric acid,  dissolve  by  digestion  on  the  water-bath,  add  a  suffi- 
cient quantity  of  a  nearly  saturated  solution  of  mercuric  chloride 
in  hydrochloric  acid  of  1*12  sp.  gr.  to  remove  the  hydrogen  sul- 
phide, and  then  proceed  as  directed. 

II.  Titrcution  with  Potassium  Permanganate. 

Here  also  the  fluid  must  contain  at  least  £  of  its  volume  of 
hydrochloric  acid  of  1.12  sp.  gr.  The  permanganate  solution, 
which  may  contain  about  1*5  grm.  of  the  crystallized  salt  in  a  litre, 
is  added  to  permanent  reddening.  The  end-reaction  is  exact,  and 
the  conversion  of  antimonious  to  antiuionic  chloride  goes  on  uni- 
formly, although  the  degree  of  dilution  may  vary,  provided  the 
above  relation  between  hydrochloric  acid  and  water  is  kept  up. 
It  is  not  well  that  the  hydrochloric  acid  should  exceed  J  of  the 
volume  of  the  fluid,  as  in  that  qase  the  end-reaction  would  be  too 
transitory.  Tartaric  acid,  at  least  in  the  proportion  to  antimony  in 
which  it  exists  in  tartar  emetic,  does  not  interfere  with  the  reac- 
tion. Hence  the  permanganate  may  be  standardized  by  the  aid  of 
solution  of  tartar  emetic  of  known  strength. 

If  you  have  to  analyze  antimonious  sulphide,  proceed  as  directed 
I.  3 ;  make  the  fluid  mixed  with  mercuric  chloride  up  to  a  certain 
volume,  allow  to  settle,  and  use  a  measured  portion  of  the  perfectly 
clear  solution  for  the  experiment. 

My  own  experiments*  have  shown  that  KESSLER'S  methods  are 
also  suitable  for  the  estimation  of  very  small  quantities  of  anti- 
mony. 


*  Zeitschr.  f.  anal.  Chem.  8,  155. 


338  DETEKMINATION.  [§  126. 

J.  Volumetric  Estimation  by  determining  the  Hydrogen  Sul- 
phide given  up  by  the  Sulphide  (R.  SCHNEIDER*). 

Both  antimonions  and  antimonic  sulphides  yield  under  the 
action  of  boiling  hydrochloric  acid  3  mol.  hydrogen  sulphide  for 
every  2  atoms  of  antimony.  Hence,  if  the  amount  of  the  gas 
evolved  under  such  circumstances  is  estimated,  the  amount  of  anti- 
mony is  known. 

For  decomposing  the  sulphide  and  absorbing  the  gas,  the  same 
apparatus  serves  as  BUNSEN  employs  for  his  iodimetric  analyses 
(§  130).  The  size  of  the  boiling-flask  should  depend  on  the  quan- 
tity of  sulphide ;  for  quantities  up  to  '4  grm.  SbQS3,  a  flask  of  100 
c.c.  is  large  enough  ;  for  *4 — 1  grm.,  use  a  200  c.c.  flask.  The  body 
of  the  flask  should  be  spherical,  the  neck  rather  narrow,  long,  and 
cylindrical.  If  the  sulphide  of  antimony  is  on  a  filter,  put  both 
together  into  the  flask.  The  hydrochloric  acid  should  not  be  too 
concentrated. 

The  determination  of  the  hydrogen  sulphide  is  best  conducted 
according  to  the  method  given  in  §  148,  b.  The  results  obtained 
by  SCHNEIDER  are  satisfactory.  If  the  precipitate  contains  anti- 
monious  chloride,  the  results  are  of  course  false,  and  this  would 
actually  be  the  case  if  on  precipitation  with  hydrogen  sulphide  the 
addition  of  the  tartaric  acid  were  omitted. 

§126. 
4.  TIN  IN  STANNOUS  COMPOUNDS,  and  5.  TIN  IN  STANNIC  COMPOUNDS. 

a.  Solution. 

In  dissolving  compounds  of  tin  soluble  in  water,  a  little  hydro- 
chloric acid  is  added  to  insure  a  clear  solution.  Nearly  all  the 
compounds  of  tin  insoluble  in  water  dissolve  in  hydrochloric  acid, 
or  in  aqua  regia.  The  hydrate  of  metastannic  acid  may  be  dissolved 
by  boiling  with  hydrochloric  acid,  decanting  the  fluid,  and  treating 
the  residue  with  a  large  proportion  of  water.  Ignited  stannic  oxide, 
and  stannic  compounds  insoluble  in  acids,  are  prepared  for  solution 
in  hydrochloric  acid,  by  reducing  them  to  the  state  of  a  fine  pow- 
der, and  fusing  in  a  silver  crucible  with  potassium  or  sodium 
hydroxide,  in  excess.  Metallic  tin  is  dissolved  best  in  aqua  regia ; 
the  solution  frequently  contains  metastannic  chloride  mixed  with 
the  stannic  chloride  (Tn.  ScHEERERf).  It  is  generally  determined, 

*  Pogg.  Anna!.  110,  634.  f  Journ.  f.  prakt.  Chcm.  N.  F.  3,  472. 


i^  126.]      TIN    IX    STANXOUS    AND    STANNIC    COMPOUNDS.         339 

however,  by  converting  it  into  stannic  oxide,  without  previous 
solution.  Acid  solutions  of  stannic  salts,  which  contain  hydrochlo- 
ric acid,  or  a  chloride,  cannot  be  concentrated  by  evaporation,  not 
even  after  addition  of  nitric  acid  or  sulphuric  acid,  without  volatili- 
zation of  stannic  chloride  taking  place. 

b.  Determination. 

Tin  is  weighed  in  the  form  of  stannic  oxide,  into  which  it  is 
converted,  either  by  the  agency  of  nitric  acid,  or  by  precipitation 
as  stannic  (or  metastannic)  acid,  or  by  precipitation  as  sulphide.  A 
great  many  volumetric  methods  of  estimating  tin  have  been  pro- 
posed. They  all  depend  on  obtaining  the  tin  in  solution  in  the 
condition  of  stannous  chloride,  and  converting  this  into  stannic 
chloride  either  in  alkaline  or  acid  solution.  A  few  only  yield  satis- 
factory results. 

We  may  convert  into 

STANNIC  OXIDE: 

a.  By  the  Agency  of  Nitric  Acid.   Metallic  tin,  and  those  com- 
pounds of  tin  which  contain  no  fixed  acid,  provided  no  compounds 
of  chlorine  be  present. 

b.  By  Precipitation  as  Stannic  (or  Metastannic)  Acid.   All  tin 
salts  of  volatile  acids,  provided  no  non- volatile  organic  .substances 
nor  ferric  salts  be  present. 

c.  By  Precipitation  a$  Sulphide.    All  compounds  of  tin  with- 
out exception. 

In  methods  a  and  c,  it  is  quite  indifferent  whether  the  tin  is 
present  as  a  stannous  or  a  stannic  compound.  The  method  b 
requires  the  tin  to  be  present  as  a  stannic  salt.  The  volumetric 
methods  may  be  employed  in  all  cases  ;  but  the  estimation  is  simple 
and  direct  only  where  the  tin  is  in  solution  as  stannous  chloride 
and  free  from  other  oxidizable  bodies,  or  can  readily  be  brought 
into  this  state.  For  the  methods  of  determining  stannous  and 
stannic  tin  in  presence  of  each  other,  I  refer  to  Section  Y.  \ 

1.  Determination  of  Tin  as  Stannic  Oxide. 

a.  By  Treating  with  Nitric  Acid. 

This  method  is  resorted  to  principally  to  convert  the  metallic 
tin  into  stannic  oxide.  For  this  purpose  the  finely-divided  metal 
is  put  into  a  capacious  flask,  and  moderately  concentrated  pure 
nitric  acid  (about  1'3  sp.  gr.)  gradually  poured  over  it ;  the  flask  is 
covered  with  a  watch  glass.  "When  the  first  tumultuous  action  of 


340  DETERMINATION.  [§  126. 

the  acid  lias  somewhat  abated,  a  gentle  heat  is  applied  until  the 
metastannic  acid  formed  appears  of  a  pure  white  color,  and  further 
action  of  the  acid  is  no  longer  perceptible.  The  contents  of  the 
flask  are  then  transferred  to  a  porcelain  dish  and  evaporated  on  a 
water-bath  nearly  to  dryness,  water  is  then  added,  and  the  precipi- 
tate is  collected  on  a  filter,  washed,  till  the  washings  scarcely  red- 
den litmus  paper,  dried,  ignited,  and  weighed.  The  ignition  is 
effected  best  in  a  small  porcelain  crucible,  according  to  §  53  ;  still 
a  platinum  crucible  may  also  be  used.  A  simple  red  heat  is  not 
sufficient  to  drive  off  all  the  water  ;  the  ignition  must  therefore  be 
finished  over  a  gas  blowpipe.  Compounds  of  tin  which  contain  no 
fixed  substances  may  be  converted  into  stannic  oxide  by  treating 
them  in  a  porcelain  crucible  with  nitric  acid,  evaporating  to  dry- 
ness,  and  igniting  the  residue.  If  sulphuric  acid  be  present,  the 
expulsion  of  that  acid  may  be  promoted,  in  the  last  stages  of  the 
process,  by  ammonium  carbonate,  as  in  the  case  of  acid  potassium 
sulphate  (§  97) ;  here  also  the  heat  must  be  increased  as  much  as 
possible  at  the  end.  For  the  properties  of  the  residue,  see  §  91. 
There  are  no  inherent  sources  of  error. 

Z>.  By  Precipitation  as  Stannic  (or  Metastannic)  Acid. 

The  application  of  this  method  presupposes  the  whole  of  the 
tin  to  be  present  in  the  state  of  stannic  salts.  Therefore,  if  a  solu- 
tion contains  stannous  salts,  either  mix  with  chlorine  water,  or  con- 
duct chlorine  gas  into  it,  or  heat  gently  with  chlorate  of  potassa, 
until  the  conversion  of  the  stannous  into  stannic  salts  is  effected. 
When  this  has  been  done,  add  ammonia  until  a  permanent  precipitate 
just  begins  to  form,  and  then  hydrochloric  acid,  drop  by  drop,  until 
this  precipitate  is  completely  redissolved ;  by  this  means  a  large 
excess  of  hydrochloric  acid  in  the  solution  will  be  avoided.  Add 
to  the  fluid  so  prepared  a  concentrated  solution  of  ammonium 
nitrate  (or  sodium  sulphate),  and  apply  heat  for  some  time,  where- 
upon the  whole  of  the  tin  will  precipitate  as  stannic  acid.  Decant 
three  times  on  to  a  filter,  then  collect  the  precipitate  on  the  latter, 
wash  thoroughly,  dry,  and  ignite.  To  make  quite  sure  that  the 
whole  of  the  tin  has  separated,  you  need  simply,  before  proceeding 
to  filter,  add  a  few  drops  of  the  clear  supernatant  fluid  to  a  hot 
solution  of  ammonium  nitrate,  or  sodium  sulphate,  when  the  for- 
mation or  non-formation  of  a  precipitate  will  at  once  decide  the 
question.  The  tin  is  also  precipitated  from  metastannic  chloride 
by  the  above  reagents. 


§  126. J      TIN   IN   STANNOU8   AND   STANNIC   COMPOUNDS.        341 

Tliis  method,  which  we  owe  to  J.  LOWENTHAL,  has  been  repeat- 
edly tested  by  him  in  my  own  laboratory,*  is  easy  and  convenient, 
and  gives  very  accurate  results.  The  decomposition  is  expressed 
by  the  equation,  SnCl4  +  4?sTa3SO4  +  3HaO  =  HaSnO3  +  4NaCl 
+  4NaHSO4,  or  in  precipitating  with  ammonium  nitrate :  SnCl4 
+  4NH4NO3  +  3H2O  =  HJSnO,  +  4XH4C1  +  4HNO3. 

Tin  may  also,  according  to  H.  RosE,f  be  completely  precipi- 
tated from  stannic  solutions  by  sulphuric  acid.  If  the  solution 
contains  metastannic  acid  or  metastannic  chloride,  the  precipitation 
is  effected  without  extraordinary  dilution ;  the  other  stannic  com- 
pounds, however,  require  very  considerable  dilution.  If  free 
hydrochloric  acid  is  absent,  the  precipitation  is  rapid ;  in  other 
cases  12  or  24  hours  at  least  are  required  for  perfect  precipitation. 
Allow  to  settle  thoroughly,  before  filtering,  wash  well  (if  hydro- 
chloric acid  was  present,  till  the  washings  give  no  turbidity  with 
silver  nitrate),  dry  and  ignite,  at  last  intensely  with  addition  of 
some  ammonium  carbonate.  The  results  obtained  by  OESTEN,  and 
communicated  by  H.  ROSE,  are  exact. 

c.  By  Precipitation  as  Stannotu  or  Stannic  Sulphide. 

Precipitate  the  dilute  moderately  acid  solution  with  hydrogen 
sulphide  water  or  gas.  If  the  tin  was  present  in  the  solution  as  a 
stannous  salt,  and  the  precipitate  consists  accordingly  of  the  brown 
stannous  sulphide,  keep  the  solution,  supersaturated  with  hydrogen 
sulphide,  standing  for  half  an  hour  in  a  moderately  warm  place, 
and  then  filter.  If,  on  the  other  hand,  the  solution  contain  a  stan- 
nic salt,  or  metastannic  acid,  and  the  precipitate  is  yellow  and  consists 
of  stannic  sulphide  mixed  with  stannic  oxide,  or  yellowish  brown 
and  consists  of  hydrated  metastannic  sulphide  mixed  with  meta- 
stannic acid  {BAKFOED,  p.  189,  TH.  SCHEEREK;*;),  put  the  fluid, 
loosely  covered,  in  a  warm  place,  until  the  odor  of  hydrogen  sul- 
phide has  nearly  gone  off,  and  then  filter.  The  washing  of  the 
stannic  sulphide  precipitate,  which  has  a  great  inclination  to  pass 
through  the  filter,  is  best  effected  with  a  concentrated  solution  of 
sodium  chloride,  the  remains  of  the  latter  being  got  rid  of  by  a 
solution  of  ammonium  acetate  containing  a  small  excess  of  acetic 
acid.  If  there  is  no  objection  to'  having  the  latter  salt  in  the  fil- 
trate, the  washing  may  be  entirely  effected  by  its  means  (BUNSEN§). 


*  Journ.  f.  prakt.  Chem.  56,  366.  f  Pogg.  Annal.  112,  164. 

\  Journ.  f.  prakt.  Chem.  N.  F.  3,  472.     §  Annal.  d.  Chem.  u.  Pharm.  106, 13. 


342  DETERMINATION.  [§  126. 

Transfer  the  dry  precipitate  as  completely  as  possible  to  a  watch 
glass,  burn  the  filter  carefully  in  a  weighed  porcelain  crucible, 
moisten  the  ash  with  nitric  acid,  ignite,  allow  to  cool,  add  the  pre- 
cipitate, cover  the  crucible,  heat  gently  for  some  time  (slight  decrep- 
itation often  occurs),  remove  the  lid  and  heat  gently  with  access  of 
air,  till  sulphur  dioxide  has  almost  ceased  to  be  formed.  (If  too 
much  heat  is  applied  at  first,  stannic  sulphide  volatilizes,  the  fumes 
of  which  give  stannic  oxide.)  Now  heat  strongly,  allow  to  cool, 
and  heat  repeatedly  with  pieces  of  ammonium  carbonate  to  a  high 
degree,  to  drive  out  the  last  portions  of  sulphuric  acid.  When  the 
weight  remains  constant  the  experiment  is  ended  (H.  HOSE).  For 
the  properties  of  the  precipitates,  see  §  91.  The  results  are  accu- 
rate. 

2.  Volumetric  Methods. 

The  determination  of  tin  by  the  conversion  of  stannous  into 
stannic  chloride  with  the  aid  of  oxidizing  agents  (potassium  dichro- 
mate  iodine,  potassium  permanganate,  etc.)  offers  peculiar  difficulties, 
inasmuch  as  on  the  one  hand  the  stannous  chloride  takes  up  oxygen 
from  the  air  and  from  the  water  used  for  dilution,  with  more  or 
less  rapidity,  according  to  circumstances ;  and  on  the  other  hand, 
the  energy  of  the  oxidizing  agent  is  not  always  the  same,  being 
influenced  by  the  state  of  dilution  and  the  presence  of  a  larger  or 
smaller  excess  of  acid. 

In  the  following  methods,  these  sources  of  error  are  avoided  or 
limited  in  such  a  manner  as  to  render  the  results  satisfactory. 

1.  Determination   of  Stannous  Chloride   ~by  Iodine  in 
Alkaline  Solution  (after  LESSEN*). 

Dissolve  the  stannous  salt  or  the  metallic  tinf  in  hydrochloric 
acid  (preferably  in  a  stream  of  carbon  dioxide),  add  Rochelle  salt, 
then  sodium  hydrogen  carbonate  in  excess.  To  the  clear  slightly 
alkaline  solution  thus  formed  add  some  starch-solution,  and  after- 
wards the  iodine  solution  of  §  146,  till  a  permanent  blue  coloration 
appears.  2  at.  free  iodine  used  corresponds  to  1  at.  tin. 
.LENSSEN'S  results  are  entirely  satisfactory. 


*  Journ.  f.  prakt.  Chem.  78,  200;  Annal.  d.  Chem.  u.  Pharm.  114,  113. 

f  The  solution  of  metallic  tin  is  much  assisted  by  the  presence  of  platinum 
foil,  which  is  accordingly  added.  LENSSEN  found  this  addition  of  platinum  to 
be  objectionable;  but  no  other  experimenter  has  observed  that  it  interferes  with 
the  accuracy  of  the  results. 


§  126.]       TIN    IX    STANNOT'S    AND    STANNIC    COMPOUNDS.         343 

2.  Determination  of  Stannous  Chloride  after  addition, 
of  Ferric  Chloride. 

The  fact  that  stannous  chloride  in  acid  solution  can  be  far  more 
accurately  converted  into  stannic  by  oxidizing  agents  after  being 
mixed  with  ferric  chloride  (or  even  with  cupric  chloride)  than 
without  this  addition,  was  first  settled  by  LOWENTHAL.*  Sub- 
sequently SxROMEYERf  published  some  experiments  leading  to  the 
same  results,  together  with  practical  remarks  on  the  best  way  of 
carrying  out  the  method  in  different  cases.  The  processes  thus 
originated,  and  which  have  been  well  tested,  are  as  follows : 

a.  The  given  substance  is  a  stannous  salt.     Dissolve  in  pure 
ferric  chloride  (free  from  ferrous  chloride)  with  addition  of  hydro- 
chloric acid,  dilute    and  add    standard    permanganate    from  the 
burette.     Kow  make  another  experiment  with  the  same  quantity 
of  water  similarly  colored  with  ferric  chloride  to  ascertain  how 
much  permanganate  is  required  to  tinge  the  liquid,  and  subtract 
the  quantity  so  used  from    the  amount  employed  in  the  actual 
analysis,  and  from  the  remainder  calculate  the  tin. 

The  reaction  between  the  tin  salt  and  the  iron  solution  is  SnCl, 
-+-Fe2Cl6=SnCl4+2FeCl2.  The  solution  thus  contains  ferrous 
chloride  in  the  place  of  stannous  salt,  the  former  being,  as  is  well 
known,  far  less  susceptible  of  alteration  from  the  action  of  free 
oxygen  than  the  latter.  2  at.  iron  found  correspond  to  1  at.  tin. 
It  must  not  be  forgotten  that  the  titration  takes  place  in  presence 
of  hydrochloric  acid.  The  results  cannot  be  considered  accurate 
unless  the  standardizing  of  the  permanganate  and  the  analysis  take 
place  under  similar  conditions  as  regards  dilution  and  amount  of 
hydrochloric  acid. 

b.  The  given  substance  is   metallic  tin.      Either   dissolve   in 
hydrochloric  acid — preferably  with  addition  of  platinum  and  in  an 
atmosphere  of  carbon  dioxide — and  treat  the  solution  according  to 
^,  or  place  the  substance  at  once  in  a  concentrated  solution  of  ferric 
chloride  mixed  with  a  little  hydrochloric  acid ;  under  these  cir- 
cumstances it  will,  if  finely  divided,  dissolve  quickly  even  in  the 
cold  and  without  evolution  of  hydrogen.       Gentle  warming    is 
unobjectionable.     Now  add  the.  permanganate.     The  reaction  is 
Sii  +  2Fe2Cl6=SnCl4  +  4FeCl2,  therefore  every  4  at,  iron  found 
reduced  correspond  to  1  at.  tin.     The  results  are  of  course  only 

*  Journ.  f.  prakt.  Chem.  76.  484.      f  Annal.  d.  Chem.  u.  Pharm.  117.  261. 


344  DETERMINATION.  [§  127. 

correct  when  iron  is  not  present,     Where  this  is  the  case,  proceed 
with  the  impure  tin  solution  according  to  c. 

c.  The  given  substance  is  stannic  chloride  or  stannic  oxide,  or  a 
compound  of  tin  containing  iron.     Dissolve  in  water  with  addition 
of  hydrochloric  acid,  place  a  plate  of  zinc  in  the  solution  and  allow 
to  stand  twelve  hours,  then   remove  the  precipitated  tin  with  a 
brush,  wash  it,  dissolve  in  ferric  chloride,  and  proceed  as  in  b. 

d.  The  given  substance  is  pure  stannic  sulphide,  precipitated 
out  of  an  acid  stannic  solution  containing  no  stannous  salt.     Mix 
with  ferric  chloride,  heat  gently,  filter  off  the  sulphur,  and  then 
add  the  permanganate.     4  at.  iron  correspond  to  1  at.  tin,  for  Sn 
S2  +  2Fe2Cl6— SnCl4  +  4FeCl2  +  2S.      The    results    obtained    by 
STROMEYER  are  quite  satisfactory.      As  regards  the  precipitated 
stannic  sulphide,  see  BARFOED,  p.  189. 

§  127. 
6.  ARSENIOUS  ACID,  and  7.  ARSENIC  ACID. 

a.  Solution. 

The  compounds  of  arseiiious  and  arsenic  acids  which  are  not 
soluble  in  water  are  dissolved  in  hydrochloric  acid  or  in  nitrohydro- 
chloric  acid.  Some  native  arsenates  require  fusing  with  sodium 
carbonate.  Metallic  arsenic,  arsenious  sulphide,  and  metallic  arsen- 
ides are  dissolved  in  fuming  nitric  acid  or  nitrohydrochloric  acid, 
or  a  solution  of  bromine  in  hydrochloric  acid;  those  metallic 
arsenides  which  are  insoluble  in  these  menstrua  are  fused  with 
sodium  carbonate  and  potassium  nitrate,  by  which  means  they  are 
converted  into  soluble  alkali  arsenates  and  insoluble  metallic  oxides, 
or  they  may  be  suspended  in  potassa  solution  and  treated  with 
chlorine  (§  164,  137  and  138).  In  this  last  manner,  too,  arsenious 
sulphide,  dissolved  in  concentrated  potassa,  may  be  very  easily  ren- 
dered soluble.  All  solutions  of  compounds  of  arsenic  which  have 
been  effected  by  long  heating  with  fuming  nitric  acid,  or  by  warm- 
ing with  excess  of  nitrohydrochloric  acid,  or  chlorine,  contain 
arsenic  acid.  A  solution  of  arsenious  acid  in  hydrochloric  acid 
cannot  be  concentrated  by  evaporation,  since  arsenious  chloride 
would  escape  with  the  hydrochloric  acid  fumes.  This,  however, 
less  readily  takes  place  if  the  solution  contains  arsenic  acid ;  in 
fact,  it  only  occurs  in  the  presence  of  a  large  proportion  of  hydro- 
chloric acid  (for  instance,  half  the  volume  of  hydrochloric  acid  of 


§  127.]  ARSENIOUS   AND    ARSENIC    ACIDS.  345 

1*12  sp.  gr.*).  It  is  therefore  advisable  in  most  cases  where  a 
hydrochloric  acid  solution  containing  arsenic  is  to  be  concentrated, 
previously  to  render  the  same  alkaline. 

b.  Determination. 

Arsenic  is  weighed  as  lead  arsenate,  a#  ammonium  magnesium 
arsenate,  as  magnesium  pyroarsenate,  as  uranyl  pyroarsenate,  or  as 
arsenious  sulphide.  The  determination  as  ammonium  magnesium 
arsenate  is  sometimes  preceded  by  precipitation  as  ammonium 
arsenio-molybdate.  The  method  recommended  by  BERTHIER  and 
modified  .by  v.  KOBELL  of  separating  the  arsenic  as  basic  ferric 
arsenate  is  only  used  in  separations.  Arsenic  may  be  estimated  also 
in  an  indirect  way,  and  by  volumetric  methods. 

We  may  convert  into 

1.  LEAD  ARSENATE  :  Arsenious  and  arsenic  acids  in  aqueous  or 
nitric  acid  solution.     (Acids  or  halogens  forming  fixed  salts  with 
lead,  and  also  ammonium  salts,  must  not  be  present.) 

2.  AMMONIUM  MAGNESIUM    ARSENATE,    or    MAGNESIUM   PYRO- 

ARSENATE I 

a.  By  direct  Precipitation.     Arsenic  acid  in  all  solutions  free 
from  bases  or  acids  precipitable  by  magnesia  or  ammonia. 

b.  Preceded  by  Precipitation  as  Ammonium  Arsenio-molyb- 
date.    Arsenic  acids  in  all  cases  where  no  phosphoric  acid  is  present, 
little  or  no  hydrochloric  acid,  nor  any  substance  which  decomposes 
molybdic  acid. 

3.  URANYL  PYROARSENATE  :  Arsenic  acid  in   all    combinations 
soluble  in  water  and  acetic  acid. 

4.  ARSENIOUS  SULPHIDE  :     All  compounds  of  arsenic  without 
exception. 

Arsenic  may  be  determined  volumetrically  in  a  simple  and 
exact  manner,  whether  present  in  the  form  of  arsenious  acid  or  an 
alkali  arsenite,  or  as  arsenic  acid  or  an  alkali  arsenate.  The  volu- 
metric methods  have  now  almost  entirely  superseded  the  indirect 
gravimetric  methods  formerly  employed  to  effect  the  determination 
of  arsenious  acid. 

1.  Determination  as  Lead  Arsenate. 
a.  Arsenic  Acid  in  Aqueous  Solution. 

A  weighed  portion  of  the  solution  is  put  into  a  platinum  or 
porcelain  dish,  and  a  weighed  amount  of  recently  ignited  pure  lead 

*  Zeitschr.  f.  Chem.  1,  448. 


346  DETERMINATION.  [§  127. 

oxide  added  (about  five  or  six  times  the  supposed  quantity  of  arse- 
nic acid  present) ;  the  mixture  is  cautiously  evaporated  to  dryness, 
and  the  residue  heated  to  gentle  redness,  and  maintained  some 
time  at  this  temperature.  The  residue  is  lead  arsenate  -f-  lead 
oxide.  The  quantity  of  arsenic  acid  is  now  readily  found  by  sub- 
tracting from  the  weight  of  the  residue  that  of  the  oxide  of  lead 
added.  For  the  properties  of  lead  arsenate,  see  §  92.  The  results 
are  accurate,  provided  the  residue  be  not  heated  beyond  gentle  red- 
ness. 

b.  Arsenious  Acid  in  Solution. 

Mix  the  solution  with  nitric  acid,  evaporate  to  a  small  bulk, 
add  a  weighed  quantity  of  lead  oxide  in  excess,  evaporate  to  dry- 
ness,  and  ignite  the  residue  most  cautiously  in  a  covered  crucible, 
until  the  whole  of  the  lead  nitrate  is  decomposed.  The  residue 
consists  here  also  of  arsenic  acid  -(-  lead  oxide.  This  method 
requires  considerable  care  to  guard  against  loss  by  decrepitation 
upon  ignition  of  the  lead  nitrate. 

2.  Estimation  as  Ammonium  Magnesium  Arsenate^  or 
Magnesium  Pyroarsenate. 

a.  By  direct  Precipitation. 

This  method,  which  was  first  recommended  by  LEVOL,  presup- 
poses the  whole  of  the  arsenic  in  the  form  of  arsenic  acid.  Where 
this  is  not  the  case,  the  solution  is  gently  heated,  in  a  capacious 
flask,  with  hydrochloric  acid,  and  potassium  chlorate  added  in 
small  portions,  until  the  fluid  emits  a  strong  smell  of  chlorous  acid ; 
it  is  then  allowed  to  stand  at  a  gentle  heat  until  the  odor  of  this 
gas  is  nearly  gone  off. 

The  arsenic  acid  solution  is  now  mixed  with  ammonia  in  excess, 
which  must  not  produce  turbidity,  even  after  standing  some  time ; 
magnesia  mixture  is  then  added  (p.  113,  §  62,  6).  The  fluid,  which 
smells  strongly  of  ammonia,  is  allowed  to  stand  24  or  48  hours  in 
the  cold,  well  covered,  and  then  filtered  through  a  weighed  filter. 
The  precipitate  is  then  transferred  to  the  filter,  with  the  aid  of 
portions  of  the  filtrate,  so  as  to  use  no  more  washing  water  than 
necessary,  and  washed  with  small  quantities  of  a  mixture  of  three 
parts  water  and  one  part  ammonia,  till  the  washings,  on  being 
mixed  with  nitric  acid  and  silver  nitrate,  show  no  opalescence.  The 
precipitate  is  dried  at  102°  to  103°,  and  weighed.  It  has  the  for- 


§  127.]  ARSENIOUS   AND   ARSENIC   ACIDS.  347 

mula  (MgNH4AsO4)3-f-H2O.*  As  the  drying  of  ammonium  mag- 
nesium arsenate  till  its  weight  is  constant,  requires  much  time  and 
repeated  weighings,  it  is  a  great  advantage  that  we  can  now  con- 
vert it  without  loss  of  arsenic  into  magnesium  pyroarsenate  (Mg2 
As2O7),  thanks  to  the  researches  of  H.  RosE,f  WITTSTEIN^:  and 
PULLER. §  For  this  purpose  first  transfer  the  dried  precipitate  as 
completely  as  possible  to  a  watch-glass,  saturate  the  filter  with 
a  solution  of  ammonium  nitrate,  dry  and  burn  it  cautiously  in  a 
porcelain  crucible.  After  cooling,  transfer  the  precipitate  to  the 
crucible,  heat  in  an  air-bath  to  about  130°,  continue  heating  for  2 
hours  on  a  sand-bath,  then  heat  for  an  hour  or  two  on  an  iron  plate 
a  little  more  strongly,  and  when  the  ammonia  has  been  thus  entirely 
expelled  ignite  strongly  for  some  time  over  the  lamp.  The  pro- 
cess may  be  shortened  by  conducting  the  heating  in  a  ROSE'S  cruci- 
ble in  a  slow  current  of  oxygen.  'The  ammonia  may  then  be 
driven  off  in  10  minutes,  and  after  the  precipitate  has  been  at  last 
strongly  heated  it  will  be  ready  to  weigh.  For  the  properties  of 
the  ammonium  magnesium  arsenate  and  magnesium  pyroarsenate, 
see  §  92.  The  method  yields  satisfactory  results,  since  the  small 
loss  of  precipitate  dissolved  in  the  filtrate  and  washings  is  coun- 
terbalanced by  the  presence  of  a  trace  of  basic  magnesium  sulphate 
(PULLER).  PULLER  with  a  quantity  of  -37  grm.  ammonium  mag- 
nesium arsenate  lost  only  a  fraction  of  a  milligramme  ;  on  the  ad- 
dition of  a  large  proportion  of  ammonium  chloride  the  loss  rose  to 
about  -002  grm.  The  correction  for  the  solubility  of  the  precipi- 
tate in  the  ammoniacal  filtrate  containining  excess  of  magnesia 
mixture  is  -001  grm.  of  (MgNH4AsO4)2-fH2O  for  30  c.c. 

b.  Preceded  by  Precipitation  as  Ammonium  Arsenio-inolyb- 
date. 

Mix  the  acid  solution,  which  must  be  free  from  phosphoric  and 
silicic  acids,  with  an  excess  of  solution  of  ammonium  molybdate. 
The  ammonium  molybdate  solution  should  have  been  previously 
mixed  with  nitric  acid  in  excess,  and  the  whole  process  is  con- 
ducted exactly  as  in  the  case  of  phosphoric  acid — see  §  134,  b,  fi. 


*  If  it  is  dried  in  a  water-bath,  the  drying  must  be  extremely  prolonged, 
or  otherwise  more  than  1  eq.  will  be  left.  After  brief  drying  in  the  water-bath 
the  compound  contains  between  1  and  3  eq.  water.  If  it  is  dried  between  105° 
and  110°,  part  of  the  1  eq.  water  is  lost. 

f  His  Handbuch  der  anal.  Chem.  6  Aufl.  2,  390. 

\  Zeitschr.  f.  anal.  Chem.  2,  19.  §  Ib.  10,  63. 


348  DETERMINATION.  [§  127. 

After  dissolving  the  ammonium  arsenio-molybdate  in  ammonia, 
neutralize  the  latter  partially  with  hydrochloric  acid.  Treat  the 
ammonium  magnesium  arsenate  as  in  a.  Results  satisfactory. 

3.  Estimation  as  Uranyl  Py  roar  senate. 

This  method  was  first  proposed  by  WERTHER.*  It  has  been 
carefully  studied  by  PuLLERf  in  my  laboratory,  and  gives  thor- 
oughly satisfactory  results.  Mix  the  arsenic  acid  solution  with 
potash  or  ammonia  in  excess,  and  then  a  good  excess  of  acetic  acid, 
(If  a  precipitate  of  ferric  or  aluminium  arsenate  here  remains 
insoluble,  the  method  would  be  inapplicable.)  Add  uranyl  acetate 
in  excess,  and  boil.  Wash  the  slimy  precipitate  of  uranyl  arsenate 
or  of  ammonium  uranyl  arsenate  by  decantation  with  boiling  water, 
and  then  transfer  to  a  filter.  The  addition  of  a  few  drops  of  chlo- 
roform to  the  partly  cool  fluid  will  hasten  the  deposition  of  the  pre- 
cipitate. Dry,  transfer  the  precipitate  to  a  watch-glass,  cleaning 
the  filter  as  much  as  possible  ;  saturate  the  latter  with  ammonium 
nitrate,  dry  it,  incinerate  in  a  porcelain  crucible,  and  add  the  pre- 
cipitate. If  the  precipitate  contains  ammonium,  heat  very  cau- 
tiously, finally  adding  nitric  acid,  or  ignite  in  oxygen.  (See  2,  a.) 
If  the  precipitate  is  free  from  ammonium,  ignite  in  the  ordinary 
way.  Ammonium  salts  do  not  interfere.  Properties  of  the  pre- 
cipitate and  residue,  §  92,  e. 

4.  Estimation  as  Arsenioiis  Sulphide. 

a.  In  solutions  of  Arsenious  Acid  or  Arsenites  free  from 
Arsenic  Acid. 

The  solution  should  be  strongly  acid  with  hydrochloric  acid. 
Precipitate  with  hydrogen  sulphide  and  expel  the  excess  with  car- 
boii  dioxide.  Pass  the  latter  through  the  solution  for  an  hour,  a 
longer  time  is  useless.  (See  §  125,  1.)  Wash  the  precipitate  thor- 
oughly and  dry  at  100°  till  the  weight  is  constant.  Particles  of 
the  precipitate  which  adhere  so  firmly  to  the  glass  that  they  can- 
not be  removed  mechanically  are  dissolved  in  ammonia  and  repre- 
cipitated  with  hydrocholric  acid.  Properties  of  the  precipitate, 
§  92.  Do  not  omit  to  test  a  weighed  portion  to  see  whether  it 
completely  volatilizes  on  heating.  If  a  residue  remains  it  is  to  be 
weighed  and  the  proportional  quantity  deducted  from  the  total 
weight  of  the  precipitate.  Results  accurate. 


*  Journ.  f.  prakt.  Chem.  43,  346.          f  Zeitschr.  f.  analyt.  Chem.  10,  72. 


§  127.]  ARSENIQUS    AND   ARSENIC    ACIDS.  349 

If  the  solution  contains  any  substance  Which  decomposes  hydro- 
gen sulphide,  such  as  ferric  chloride,  chromic  acid,  etc.,  the  precip- 
itate produced  in  the  cold  contains  an  admixture  of  finely  divided 
sulphur.  It  should  be  collected  in  the  same  manner  on  a  filter 
dried  at  100°,  and  weighed,  washed  and  dried.  Extract  the 
admixed  sulphur  with  purified  carbon  disulphide  (which  should 
leave  no  residue  on  evaporation),  continuing  till  the  fluid  which 
runs  through  leaves  no  residue.  Dry  at  100°  till  the  weight  is 
constant.  From  experiments  made  in  my  laboratory  it  appears 
that  the  results  thus  obtained  are  quite  accurate,  even  when  the 
amount  of  admixed  sulphur  is  large  ;  but  the  precipitation  must 
have  been  effected  in  the  cold.  If,  on  the  contrary,  heat  is  used, 
the  sulphur  is  in  the  form  of  small  agglutinated  grains  and  cannot 
be  completely  extracted  by  cold  carbon  disulphide  on  the  filter. 
However,  it  may  be  extracted  by  removing  the  precipitate  from  the 
filter  and  repeatedly  digesting  it  with  the  disulphide  on  a  water- 
bath  (PULLER*). 

Instead  of  purifying  the  arsenious  sulphide  you  may  estimate 
the  arsenic  in  the  mixture  of  the  sulphide  with  sulphur  as  follows : 
Dissolve  the  precipitate  in  strong  potash,  and  pass  chlorine  into  the 
solution  (§  148,  II.  2,  b).  The  arsenic  and  the  sulphur  are  con- 
verted into  arsenic  and  sulphuric  acid  respectively  ;  the  former 
may  be  estimated  according  to  2,  a,  or  the  latter  according  to  §  132. 
In  the  latter  case,  deduct  the  sulphur  found  from  the  weight  of  the 
arsenical  precipitate.  There  is  no  loss  of  arsenic  in  this  process 
from  volatilization  of  the  chloride,  as  the  solution  remains  alkaline. 
The  object  may  also  be  conveniently  attained  by  the  use  of  nitric 
acid.  A  very  strong  fuming  acid,  of  86°  boiling  point,  is 
employed  ;  an  acid  of  1-42  sp.  gr.  which  boils  at  a  higher  tempera- 
ture does  not  answer  the  purpose,  as  the  separated  sulphur  would 
fuse,  and  its  oxidation  would  be  much  retarded.  The  well  dried 
precipitate  is  shaken  into  a  small  porcelain  dish,  treated  with  a  tol- 
erably large  excess  of  the  fuming  nitric  acid,  the  dish  immediately 
covered  with  a  watch-glass,  and  as  soon  as  the  turbulence  of  the 
first  action  has  somewhat  abated,  heated  on  a  water-bath  till  all  the 
sulphur  has  disappeared,  and  the  nitric  acid  has  evaporated  to  a 
small  volume.  The  filter  to  which  the  unremovable  traces  of 
arsenious  sulphide  adhere  is  treated  separately  in  the  same  manner, 

*  Zeitschr.  f.  anal.  Chem.  10,  46  et  seq. 


350  DETERMINATION.  [_§  127. 

the  complete  destruction  of  the  organic  matter  being  finally  effected 
by  gently  warming  the  somewhat  dilute  solution  with  potassium 
chlorate  (BUNSEN*).  Or  the  filter  may  instead  be  extracted  with 
ammonia,  the  solution  evaporated  in  a  separate  dish,  and  the  resid- 
ual sulphide  treated  as  above.  In  the  mixed  solution  the  arsenic 
acid  is  finally  precipitated  as  ammonious  magnesium  arsenate. 
(§  127,  2,  a).  Treatment  of  the  impure  precipitate  with  ammonia, 
whereby  the  sulphide  is  dissolved,  and  the  sulphur  is  supposed  to 
remain  behind,  only  gives  approximate  results,  as  the  ammoniacal 
solution  of  arsenious  sulphide  takes  up  a  little  sulphur. 

b.  In  solutions  of  Arsenic  Acid,  or  of  a  mixture  of  the  two 
Oxides  of  Arsenic. 

Heat  the  solution  in  a  flask  (preferably  on  an  iron  plate)  to 
about  70°,  and  conduct  hydrogen  sulphide  at  the  same  time  into 
the  fluid,  as  long  as  precipitation  takes  place.  The  precipitate 
formed  is  always  a  mixture  of  sulphur  and  arsenious  sulphide,  since 
the  arsenic  acid  is  first  reduced  to  arsenious  acid  with  separation  of 
sulphur,  and  then  the  latter  is  decomposed  (H.  Rossf).  Only  in 
the  case  when  a  sulphosalt  containing  pentasulphide  of  arsenic  is 
decomposed  with  an  acid,  is  the  precipitate  actually  pentasulphide, 
and  not  merely  a  mixture  of  sulphur  with  arsenious  sulphide  (A. 
FUCHS^:).  To  convert  this  mixture  of  arsenious  sulphide  and 
granular  sulphur  into  pure  arsenious  sulphide,  suitable  for  weigh- 
ing, treat  it  a,s  follows :  Extract  the  washed  and  still  moist  pre- 
cipitate on  the  filter  with  ammonia,  wash  the  residual  sulphur, 
precipitate  the  solution  with  hydrochloric  acid  without  heat,  filr 
ter,  dry,  extract  with  carbon  disulphide,  dry  at  100°,  and  weigh. 
Results  accurate.  The  mixture  of  arsenious  sulphide  and  sulphur 
obtained  by  hot  precipitation  may,  of  course,  also  be  estimated 
directly  or  indirectly  after  one  of  the  other  methods  in  4,  a. 

5.  Volumetric  Methods. 

a.  Method  which  presupposes  the  presence  of  Arsenious  Acid. 

BUNSEN'S  method.§  This  method  is  based  upon  the  following 
facts : 

aa.  If  potassium  dichromate  is  boiled  with  concentrated  hydro- 
chloric acid,  6  at.  chlorine  are  disengaged  to  every  2  mol.  chromic 
acid  2CrO3  +  12HC1  =  Cr2Cl6  +  6H2O  -f-  601. 

*  Annal.  d.  Chem.  u.  Pharm.  106,  10.  f  Pogg.  Annal.  107,  186. 

JZeitschr.  f.  anal.  Chem.  1,  189.       §  Annal.  d.  Chem.  u.  Pharm.  86,  290. 


§  127.]  ARSENIOUS   AND   ARSENIC   ACIDS.  351 

bb.  But  if  arsenious  acid  is  present  (not  in  excess)  there  is  not 
the  quantity  of  chlorine  disengaged  corresponding  to  the  chromic 
acid,  but  so  much  less  of  that  element  as  is  required  to  convert  the 
arsenious  into  arsenic  acid  (H3AsO3  +  2C1  +  H2O  =  H3AsO4  -f  2 
HC1).  Consequently,  for  every  2  at.  chlorine  wanting  is  to  be 
reckoned  1  mol.  arsenious  acid. 

cc.  The  quantity  of  chlorine  is  estimated  by  determining  the 
quantity  of  iodine  liberated  by  it  from  potassium  iodide. 

These  are  the  principles  of  BUNSEN'S  method.  For  the  manner 
of  execution  I  refer  to  the  Estimation  of  Chromic  Acid. 

b.  Method,  which  presupposes  the  presence  of  A.  r seme  Acid. 

This  method  depends  on  the  precipitation  of  the  arsenic  acid 
by  uranium  solution  and  the  recognition  of  the  end  of  the  reaction 
by  means  of  potassium  ferrocyanide.  It  is  therefore  the  same  as 
was  suggested  for  phosphoric  acid  by  LECOMTE,  and  brought  into- 
use  by  NEUBAUER,*  and  afterwards  by  PiNcus.f 

BODEKER,^:  who  first  employed  the  process  for  arsenic  acid, 
recommends  the  employment  of  a  solution  of  uranyl  nitrate,  as 
this  is  more  permanent  than  the  hitherto  used  acetate,  which  is 
gradually  decomposed  by  the  action  of  light. 

The  uranium  solution  has  the  correct  degree  of  dilution,  if  it 
contains  about  17  grm.  of  uranium  in  1  litre.  It  should  contain 
as  little  free  acid  as  possible.  The  determination  of  its  value  may 
be  effected  with  the  aid  of  pure  sodium  arsenate  or  by  means  of 
arsenious  acid — the  latter  is  converted  into  arsenic  acid  by  boiling 
with  fuming  nitric  acid.  The  solution  is  rendered  strongly  alka- 
line with  ammonia,  and  then  distinctly  acid  with  acetic  acid.  The 
uranium  solution  is  now  run  in  from  the  burette  slowly,  the  liquid 
being  well  stirred  all  the  while,  till  a  drop  of  the  mixture  spread 
out  on  a  porcelain  plate,  gives  with  a  drop  of  potassium  ferrocya- 
nide placed  in  its  centre,  a  distinct  reddish-brown  line  where  the 
two  fluids  meet.  The  height  of  the  fluid  in  the  burette  is  now 
read  off,  the  level  of  the  mixture  in  the  beaker  is  marked  with  a 
strip  of  gummed  paper,  and  the  beaker  is  emptied  and  washed, 
filled  with  water  with  addition  of  about  as  much  ammonia  and 
acetic  acid  as  was  before  employed,  and  the  uranium  solution  is 
cautiously  dropped  in  from  the  burette,  till  a  drop  taken  out  of  the 
beaker  and  tested  as  above,  gives  an  equally  distinct  reaction.  The 

*  Archiv  fur  wissenschaftliche  Heilkunde,  4,  228. 

f  Journ.  f.  prakt.  Chem.  76,  104.       \  Anna!,  de  Chem.  u.  Pharm.  117,  195. 


352  DETERMINATION.  [§  127. 

quantity  of  uranium  solution  used  in  this  last  experiment  is  the 
excess,  which  must  be  added  to  make  the  end-reaction  plain  for  the 
dilution  adopted.  This  amount  is  subtracted  from  that  used  in  the 
first  experiment,  and  we  then  know  the  exact  value  of  the  uranium 
solution  with  reference  to  arsenic  acid. 

In  an  actual  analysis,  the  arsenic  is  first  brought  into  the  form 
of  arsenic  acid,  a  clear  solution  is  obtained  containing  ammonium 
acetate  and  some  free  acetic  acid,*  and  the  process  is  conducted 
exactly  as  in  determining  the  value  of  the  standard  solution.  The 
experiment  to  ascertain  the  correction  must  not  be  omitted  here, 
otherwise  errors  are  sure  to  arise  from  the  different  degrees  of  dilu- 
tion of  the  arsenic  acid  solutions  used  in  the  determination  of  the 
value  of  the  standard  solution  and  in  the  actual  analyses.  The  results 
of  two  determinations  of  arsenic  given  by  BODEKEK  are  satisfactory. 
To  execute  the  method  well  requires  practice.  The  results  are  not 
exact  enough  unless  the  conditions  as  regards  amount  and  quality 
of  alkali  salts  are  nearly  similar  in  the  standardizing  of  the  uranium 
solution  and  in  its  use.  Compare  WArrz.f 

6.  Estimation  of  Arsenious  Acid  by  Indirect  Gravimet- 
ric Analysis. 

a.  ROSE'S  method.  Add  to  the  hydrochloric  acid  solution,  in 
the  preparation  of  which  care  must  be  taken  to  exclude  oxidizing 
substances,  a  solution  of  sodium-  or  ammonium-auric  chloride  in 
excess,  and  digest  the  mixture  for  several  days,  in  the  cold,  or,  in 
the  case  of  dilute  solutions,  at  a  gentle  warmth ;  then  weigh  the 
separated  gold  as  directed  in  §  123.  Keep  the  filtrate  to  make 
quite  sure  that  no  more  gold  will  separate.  2  at.  gold  correspond 
to  3  mol.  arsenious  acid. 

1.  YOIIL'S^  method.  Mix  the  solution  with  a  weighed  quan- 
tity of  potassium  dichromate,  and  free  sulphuric  acid ;  estimate  the 
chromic  acid  still  present  by  the  method  given  in  §  130,  <?,  and 
deduce  from  the  quantity  of  that  acid  consumed  in  the  process,  i.e., 
reduced  by  the  arsenious  acid,  the  quantity  of  the  latter,  after  the 
formula  3H3 AsO3  +  2CrO3  =  3H3AsO4  +  Cr2O3. 


*  Alkalies,  alkali  earths,  and  zinc  oxide  may  be  present,  but  not  such  metals 
as  yield  colored  precipitates  with  ferrocyanide  of  potassium,  as,  for  instance, 
-copper.  f  Zeitschr.  f.  anal.  Chem.  10,  182. 

\  Annal.  de  Chem.  u.  Pharm.  94,  219. 


§  128.]  MOLYKDIC    ACID.  353 

Supplement  to  the  Sixth.  Group. 

§128. 
8.  MOLYBDIC  Acm. 

Molybdic  acid  is  converted,  for  the  purpose  of  its  determina- 
tion, either  into  molybdenum  dioxide,  or  into  lead  molybdate,  or 
into  molybdenum  disulphide. 

a.  Molybdic  anhydride  (Mo()3),  and  also  ammonium  molybdate, 
may  be  reduced  to  dioxide  by  heating  in  a  current  of  hydrogen  gas. 
This  may  be  done  either  in  a  porcelain  boat,  placed  in  a  wide  glass 
tube,  or  in  a  platinum  or  porcelain  crucible  with  perforated  cover 
(§  108,  fig.  50).     The  operation  is  continued  till  the  weight  remains 
constant.      The  temperature  must  not   exceed  a  gentle  redness, 
otherwise  the  dioxide  itself  might  lose  oxygen  and  become  partially 
converted  into  metal.     In  the  case  of  ammonium  molybdate  the 
heat  must  be  very  low  at  first  on  account  of  the  frothing.     If  you 
have  a  platinum  tube  it  is  safer  to  ignite  the  molybdic  acid  in  this 
for  2  or  3  hours  in  a  slow  current  of  hydrogen,  thus  reducing  it  to 
the  metallic  state.     When  reducing  to  dioxide  the  contents  of  the 
crucible  are  frequently  gray  below,  and  brown  above  (KAMMELS- 
BERG*). 

b.  The  following  is  the  best  method  of  precipitating  molybdic 
acid  from  an  alkaline  solution  :  Dilute  the  solution,  if  necessary, 
neutralize  the  free  alkali  with  nitric  acid,  and  allow  the  carbonic 
acid,  which  may  be  liberated  in  the  process,  to  escape,  then  add 
neutral  mercurous  nitrate.     The  yellow  precipitate  formed  appears 
at  first  bulky,  but  after  several  hours'  standing  it  shrinks  ;  it  is 
insoluble   in   the   fluid,  which  contains   an   excess  of   mercurous 
nitrate.     Collect  on  a  filter,  and  wash  with  a  dilute  solution  of  mer- 
curous nitrate,  as  it  is  slightly  soluble  in  pure  water.     Dry,  remove 
the  precipitate  as  completely  as  practicable  from  the  filter,  and  deter- 
mine the  molybdenum  in  it  as  directed  in  a  (H.  ROSE)  ;  or  mix  the 
precipitate,  together  with  the  filter-ash,  with  a  weighed  quantity 
of  ignited  lead  oxide,  and  ignite  until  all  the  mercury  is  expelled  ; 
then  add  some  ammonium  nitrate,  ignite  again  and  weigh.     The 
excess  obtained,  over  and  above  the  weight  of  the  lead  oxide  used, 
is  molybdenum  trioxide  (S 


*  Pogg.  Aiinal.  127,  281;  Zeitschr.  f.  anal.  Chem.  5,  203. 
f  Journ.  f.  prakt.  Chem.  67,  472. 


354  DETERMINATION.  |  §  128. 

c.  CHATARD*  recommends  estimating  molybdic  acid  in  the  solu- 
tion of  its  alkali  salts  by  adding  lead  acetate  in  slight  excess  to  the 
boiling  solution  and  boiling  for  a  few  minutes.     The  precipitate 
which  is  at  first  milky  becomes  granular,  deposits  well,  and  may  be 
easily  washed  with  hot  water.     It  is  dried,  removed  from  the  filter 
as  much  as  possible,  ignited  and  weighed  as  PbMoO4;    The  method 
is  only  applicable  for  solutions  of  pure  alkali  molybdates. 

d.  The  precipitation  of  molybdenum  as  sulphide  is  always  a 
difficult  operation.     If  the  acid  solution    is   supersaturated  with 
hydrogen  sulphide,  warmed,  and  filtered,  the  filtrate  and  washings 
are  generally  still  colored.     They  must,  accordingly,  be  warmed, 
and  hydrogen  sulphide  again  added,  and  the  operation  must  after- 
wards, if  necessary,  be  repeated  until  the  washings  appear  almost 
colorless.    The  precipitation  succeeds  better  when  the  molybdenum 
sulphide  is  dissolved  in  a  relatively  large  excess  of  ammonium  sul- 
phide, and,  after  the  fluid  has  acquired  a  reddish-yellow  tint,  precipi- 
tated with  hydrochloric  acid.     ZENKERf  advises  then  to  boil,  until 
the  hydrogen  sulphide  is  expelled,  and  to  wash  with  hot  water,  at 
first  slightly  acidified.     To  make  quite  sure  that  all  the  molyb- 
denum is  precipitated,  treat  the  filtrate  and  washings  again  with 
hydrogen  sulphide  and  allow  to  stand  for  some  time.     The  brown 
molybdenum  sulphide  is  collected  on  a  weighed  filter,  and   the 
molybdenum  determined  in  an  aliquot  part  of  it,  by  gentle  ignition 
in  a  current  of  hydrogen  gas,  as  in  a.     The  brown  molybdenum 
sulphide  changes  in  this  process  to  the  gray  disulphide  (H.  ROSE). 

e.  F.  PISANI:]:  gives  the  following  method  for  estimating  molyb- 
dic acid  volumetrically.     Digest  the  molybdic  acid  with  hydro- 
chloric acid  and  zinc,  dissolving  any  precipitate  which  may  form 
from  want  of  acid  and  also  the  excess  of  zinc.     The  molybdic  acid 
is  thus  reduced  to  a  molybdenum  salt  corresponding  to  molybdenum 
sesquioxide.     Convert  the  molybdenum  in  this  solution  again  into 
molybdic  acid  by  standard  permanganate  of  potash.     The  brown 
color  of  the  solution  turns  first  green,  and  then  disappears.     RAM- 
MELSBERG§  confirms  the  statements  of  PISANI. 


*  Sill.  Amer.  Journ.  (3),  1,  416.  \  Journ.  f.  prakt.  Chem.  58,  259. 

t  Compt.  rend.  59,  301. 

§  Pogg.  Annal.  127,  281;  Zeitschr.  f.  anal.  Chem.  5,  203. 


;$§  129,  130.]  ARSENIOUS,  ARSENIC  AND  CHROMIC  ACIDS.    355 
II.    DETERMINATION  OF  ACIDS  IN  COMPOUNDS  CONTAINING 

ONLY  ONE  ACID,   FREE    OR    COMBINED ;— AND    SEPARATION 
OF  ACID  FROM  BASIC  RADICALS. 

First  Group. 

FIRST     DIVISION. 

ARSENIOUS  ACID — ARSENIC  ACID — CHROMIC  ACID — (Selenious 
Acid,  Sulphurous  and  Hyposulphurous  Acids,  lodic  Acid). 

§129. 
1.  ARSENIOUS  AND  ARSENIC  ACIDS. 

These  have  been  already  treated  of  among  the  bases  (§  127)  on 
account  of  their  behavior  with  hydrogen  sulphide  ;  they  are  merely 
mentioned  here  to  indicate  the  place  to  which  they  properly  be- 
long. The  methods  of  separating  them  from  the  bases  will  be 
found  in  Section  V. 

§130. 
2.  CHROMIC  ACID. 

I.  DETERMINATION. 

Chromic  acid  is  determined  either  as  chromic  oxide  or  lead 
chromate.  But  it  may  be  estimated  also  from  the  quantity  of  car- 
bon dioxide  disengaged  by  its  action  upon  oxalic  acid  in  excess, 
and  also  by  volumetric  analysis.  In  employing  the  first  method 
it  must  be  borne  in  mind  that  1  mol.  chromic  oxide  corresponds  to 
2  mol.  chromic  acid. 

a.  Determination  as  Chromic  Oxide. 

a.  The  chromic  acid  is  reduced  to  the  state  of  a  chromic  salt 
and  the  amount  of  chromium  in  the  latter  determined  (§  106).  The 
reduction  is  effected  either  by  heating  the  solution  with  hydro- 
chloric acid  and  alcohol ;  or  by  mixing  hydrochloric  acid  with  the 
solution,  and  conducting  hydrogen  sulphide  into  the  mixture  ;  or 
by  adding  a  strong  solution  of  sulphurous  acid,  and  applying  a  gen- 
tle heat.  With  concentrated  solutions  the  first  method  is  gener- 
ally resorted  to,  with  dilute  solutions  one  of  the  two  latter.  With 
respect  to  the  first  method,  I  have  to  remark  that  the  alcohol  must 
be  expelled  before  the  chromium  can  be  precipitated  as  hydroxide 


356  DETERMINATION.  [§  130. 

by  ammonia ;  and  with  respect  to  the  second,  that  the  solution 
supersaturated  with  hydrogen  sulphide  must  be  allowed  to  stand  in 
a  moderately  warm  place,  until  the  separated  sulphur  has  com 
pletely  subsided.  The  results  are  accurate,  unless  the  weighed  pre- 
cipitate contains  silica  and  lime,  which  is  always  the  case  if  the  pre- 
cipitation is  effected  in  glass  vessels. 

/?.  The  neutral  or  slightly  acid  (nitric  acid)  solution  is  precipi- 
tated with  mercurous  nitrate,  after  long  standing  the  red  precipitate 
of  mercurous  chromate  is  filtered  off,  washed  with  a  dilute  solution 
of  mercurous  nitrate,  dried,  ignited,  arid  the  residuary  chromic 
oxide  weighed  (H.  ROSE).  Results  accurate. 

b.  Determination  as  Lead  Chromate. 

The  solution  is  mixed  with  sodium  acetate  in  excess,  and  acetic 
acid  added  until  the  reaction  is  strongly  acid ;  the  solution  is  then 
precipitated  with  neutral  lead  acetate.  The  washed  precipitate  is 
either  collected  on  a  weighed  filter,  dried  in  the  water-bath,  and 
weighed;  or  it  is  gently  ignited  as  directed  §  53,  and  then 
weighed.  For  the  properties  of  the  precipitate,  see  §  93,  2.  Results 
accurate. 

c.  Determination  ly  means  of  Oxalic  Acid  (after  VOHL). 
When  chromic  acid  and  oxalic  acid  are  brought  together  in  the 

presence  of  water  and  excess  of  sulphuric  acid,  chromic  sulphate 
and  carbon  dioxide  are  formed,  3H2C2O4  +  2H2OO4  +  3H,SO4  = 
6CO2-f-  Cra(SO4)3+  8H2O.  Accordingly  the  amount  of  chromic  acid 
can  be  calculated  from  the  weight  of  carbon  dioxide  evolved.  The 
process  is  the  same  as  in  the  analysis  of  manganese  ores  (§  203).  1 
part  of  chromic  acid  requires  2J  parts  of  sodium  oxalate.  If  it  is 
intended  to  determine  potassium  or  sodium  in  the  residue,  ammo- 
nium oxalate  is  used. 

d.  Determination  l>y  Volumetric  Analysis. 

a.  SCHWARZ'S  method. 

The  principle  of  this  very  accurate  method  is  identical  with 
that  upon  which  PENNY'S  method  of  determining  iron  is  based  (§  112, 
2,  b).  The  execution  is  simple  :  acidify  the  not  too  dilute  solution 
of  the  chromate  with  sulphuric  acid,  add  in  excess  a  measured  quan- 
tity of  solution  of  a  ferrous  salt,  the  strength  of  which  you  have 
previously  ascertained,  according  to  the  directions  of  §  112,  2,  «,  or 
&,  or  the  solution  of  a  weighed  quantity  of  ammonium  ferrous  sul- 
phate, free  from  ferric  salt,  and  then  determine  in  the  manner 


§  130.]  CHROMIC    ACID.  357 

directed  §  112,  2,  a,  or  £,  the  quantity  of  ferrous  iron  remaining. 
The  difference  shows  the  amount  of  iron  that  has  been  converted 
by  the  chromic  acid  from  a  ferrous  to  a  ferric  salt.  1  grm.  of  iron 
corresponds  to  0-5981  of  chromic  anhydride  (CrOs).  To  determine 
the  chromic  acid  in  lead  chromate,  the  latter  is,  after  addition  of 
the  ammonium  ferrous  sulphate,  most  thoroughly  triturated  with 
hydrochloric  acid,  water  added,  and  the  analysis  then  proceeded 
with. 

ft.  BUNSEN'S  method* 

If  a  chromate  is  boiled  with  an  excess  of  fuming  hydrochloric 
acid,  there  are  disengaged  for  every  atom  of  chromium  3  at.  chlo- 
rine ;  for  instance,  K.Cr.O,  +  (HC1)14  =  (KC1),  +  Cr2Cl6  +  601  + 
THa  O.  If  the  escaping  gas  is  conducted  into  solution  of  potassium 
iodide  in  exces,  the  3  at.  chlorine  set  free  3  at.  iodine.  The  libera- 
ted iodine  may  next  be  determined  as  described  in  §  146.  380'55 
of  iodine  correspond  to  100*48  of  chromic  anhydride  (CrO8). 

The  analytical  process  is  conducted  as  follows :  Put  the  weighed 
sample  of  the  chromate  (say  •  3  to  •  -1  grm.)  into  the  little  flask  d, 
tig.  55  (blown  before  the  lamp,  and  holding  only  from  36  to  40 
c.c.),  and  nil  the  flask  two 
thirds  with  pure  fuming 
hydrochloric  acid  (free 
from  Cl  and  SO,),  add  a 
compact  lump  of  magne- 
site,  to  keep  up  a  con- 
stant current  of  gas  and 
prevent  the  fluid  from 
receding.  Connect  the 
bulbed  evolution  tube  a 
with  the  neck  of  the  flask  by  means  of  a  stout  india-rubber  tube 
c.  As  shown  in  the  engraving,  a  is  a  bent  pipette,  drawn  out  at 
the  lower  end  into  an  upturned  point.  A  loss  of  chlorine  need  not 
be  apprehended  on  adding  the  hydrochloric  acid,  as  the  disengage- 
ment of  that  gas  begins  only  upon  the  application  of  heat.  Insert 
the  evolution  tube  into  the  neck  of  the  retort,  which  is  one-third 
filled  with  solution  of  potassium  iodide. f  This  retort  holds  about 


*  Annal.  d.  Chem.  u.  Pharm.  86,  279. 

t  1  part  of  pure  potassium  iodide,  free  from  iodic  acid,  dissolved  in  10  parts  of 
water.  The  fluid  must  show  no  brown  tint  immediately  after  addition  of  dilute 
sulphuric  acid. 


358  DETERMINATION.  [§  130. 

160  c.c.  The  neck  presents  two  small  expansions,  blown  before 
the  lamp,  and  intended,  the  lower  one,  to  receive  the  liquid  which 
is  forced  up  during  the  operation,  the  upper  one  to  serve  as  an 
additional  guard  against  spirting.  Apply  heat  now,  cautiously,  to 
the  little  flask.  After  two  or  three  minutes  ebullition  the  whole 
of  the  chlorine  has  passed  over,  and  liberated  its  equivalent  quan- 
tity of  iodine  in  the  potassium  iodide  solution.  When  the  ebulli- 
tion is  at  an  end,  take  hold  of  the  caoutchouc  tube  c  with  the  left 
hand,  and,  whilst  steadily  holding  the  lamp  under  the  flask  with 
the  right,  lift  a  so  far  out  of  the  retort  that  the  curved  point  is  in 
the  bulb  h.  Now  remove  first  the  lamp,  then  the  flask,  dip  the 
retort  in  cold  water  to  cool  it,  and  shake  the  fluid  in  it  about  to  effect 
the  complete  solution  of  the  separated  iodine  in  the  excess  of  potas- 
sium iodide  solution.  When  the  fluid  is  quite  cold,  transfer  it  to  a 
beaker,  rinsing  the  retort  into  the  beaker,  and  proceed  as  directed 
§  146.  The  method  gives  very  satisfactory  results.  The  apparatus 
here  recommended  diifers  slightly  from  that  used  by  BUNSEN,  the 
retort  of  the  latter  having  only  one  bulb  in  the  neck,  and  the  evo- 
lution tube  no  bulb,  being  closed  instead,  at  the  lower  end,  by  a 
glass  or  caoutchouc  valve,  which  permits  the  exit  of  the  gas  from 
the  tube,  but  opposes  the  entrance  of  the  fluid  into  it.  I  think  the 
modifications  which  I  have  made  in  BUNSEN'S  apparatus  are  calcu- 
lated to  facilitate  the  success  of  the  operation.  Instead  of  this 
apparatus,  that  described  §  142  may  also  be  very  conveniently  used. 

II.  SEPARATION  OF  CHROMIC  ACID  FROM  THE  BASIC 
RADICALS. 

a.  Of  the  First  Group. 

a.  Reduce  the  chromic  acid  to  a  chromic  salt,  as  directed  in  I., 
and  separate  the  chromium  from  the  alkalies  as  directed  in  §  155. 

ft.  Mix  the  potassium  or  sodium  chromate  with  about  5  parts 
of  dry  pulverized  ammonium  chloride,  and  heat  the  mixture  cau- 
tiously. The  residue  contains  the  chlorides  of  the  alkali  metals 
and  chromic  oxide,  which  may  be  separated  by  means  of  water. 

y.  Precipitate  the  chromic  acid  according  to  I.,  «,  /?,  and  sep- 
arate the  mercury  and  alkali  metals  in  the  filtrate  by  §  1 02. 

h.  Of  the  Second  Group. 

a.  Fuse  the  compound  with  4  parts  of  sodium  and  potassium 
carbonates,  and  treat  the  fused  mass  with  hot  water,  which  dis- 
solves the  chromic  acid  in  the  form  of  an  alkali  chromate.  The 


§  130.]  CHROMIC   ACID.  359 

residue  contains  the  alkali  earth  metals  in  the  form  of  carbonates ; 
but  as  they  contain  alkali,  they  cannot  be  weighed  directly.  The 
chromic  acid  in  the  solution  is  determined  as  in  I.  Strontium  and 
calcium  chromates  may  be  decomposed  by  boiling  with  potassium 
or  sodium  carbonate.  Barium  chromate  may  also  be  decomposed 
in  the  same  way,  but  the  boiling  must  be  repeated  a  second  time 
with  fresh  solution  of  alkali  carbonate  (H.  KOSE). 

ft.  Dissolve  in  hydrochloric  acid,  reduce  the  chromic  acid 
according  to  I.,  #,  and  separate  the  chromium  from  the  alkali 
earth  metals  according  to  §  156. 

y.  Magnesium  chromate,  as  well  as  other  chromates  of  the 
alkali  earth  metals  soluble  in  water,  may  be  easily  decomposed  also, 
by  determining  the  chromic  acid  according  to  L,  a,  /?,  or  L,  b,  and 
separating  the  magnesium,  etc.,  in  the  filtrate  from  the  excess  of 
the  salt  of  mercury  or  lead  as  directed  §  162. 

d.  Barium  strontium  and  calcium  chromates  may  also  be 
decomposed  by  the  method  described  II.,  «,  ft.  Compare  BAHK, 
Analysis  of  barium  and  calcium  dichromates,  etc.* 

c.   Of  the  Third  Group. 

a.  from  Aluminium. 

If  you  have  chromic  acid  to  separate  from  aluminium  in  acid 
solution,  precipitate  the  aluminium  with  ammonia  or  ammonium 
carbonate  (§  105,  a)7  and  determine  the  chromic  acid  in  the  filtrate 
according  to  I.  If  the  washed  aluminium  hydroxide  has  a  yellow 
color,  treat  on  the  filter  with  ammonia,  and  wash  with  boiling 
water  :  this  will  remove  the  last  traces  of  chromic  acid.  However, 
a  little  aluminium  hydroxide  dissolves  in  the  ammonia,  therefore 
heat  the  ammoniacal  fluid  in  a  platinum  dish  till  it  has  almost  lost 
its  alkaline  reaction,  and  collect  on  a  filter  the  flocks  of  aluminium 
hydroxide  which  separate,  and  add  them  to  the  principal  precip- 
itate. 

ft.  From  Chromium. 

aa.  Determine  in  one  portion  the  quantity  of  the  chromic  acid 
according  to  I.,  #,  or  I.,rf,  OL,  or  ft,  and  in  another  portion  the  total 
amount  of  the  chromium,  by  converting  it  into  sesquioxide  by  cau- 
tious ignition  with  ammonium  chloride,  or  by  L,  #,  or  by  convert- 
ing it  entirely  into  chromic  acid  by  §  106,  2. 

bb.  In  many  cases  the  chromic  acid  may  be  precipitated  accord- 

*  Journ.  f.  prakt.  Chem.  60,  60. 


360  DETERMINATION.  [§  130. 

ing  to  I.,  a,  ft,  or  I.,  I.     The  chromium  and  mercury,  or  lead,  in 
the  filtrate,  are  separated  as  directed  §  162. 

cc.  The  hydrated  compounds  of  sesquioxide  of  chromium  with 
chromium  trioxide,  or  chromic  chromates,  such  as  are  obtained  by 
precipitating  a  solution  of  chromic  salt  with  potassium  chromate, 
etc.,  may  also  be  analyzed  by  ignition  in  a  stream  of  dry  air,  in  a 
bulb  tube,  to  which  a  calcium  chloride  tube  is  attached  (fig.  25, 
§  36).  The  loss  of  weight  represents  the  joint  amount  of  oxygen 
and  water  that  have  escaped.  If  the  increment  of  the  CaCl3  tube 
is  deducted,  we  shall  have  the  oxygen.  Now  every  3  at.  oxygen 
correspond  to  2  mol.  CrO,.  The  amount  of  the  latter  being  thus 
calculated,  we  have  only  to  subtract  its  equivalent  quantity  of  ses- 
quioxide from  the  weight  of  residue  after  the  ignition,  and  the 
remainder  is  the  quantity  of  sesquioxide  originally  present.  VOGEL* 
and  also  STOKER  and  ELLioxf  have  employed  this  method. 

d.  Of  the  Fourth  Group. 

a.  Proceed  as  directed  in  b,  ot.  Upon  treating  the  fused  mass 
with  hot  water,  oxides  of  the  basic  metals  are  left.  In  the  case  of 
manganese  the  fusion  must  be  effected  in  an  atmosphere  of  carbon 
dioxide.  Apparatus,  fig.  50  in  §  108. 

ft.  Reduce  the  chromic  acid  as  directed  in  I.,  #,  and  separate 
the  chromium  from  the  metals  in  question,  as  directed  in  §  160. 

e.  Of  the  Fifth  and  Sixth  Groups. 

a.  Acidify  the  solution,  and  precipitate,  either  at  once  or  after 
reduction  of  the  chromic  acid  by  sulphurous  acid,  with  hydrogen 
sulphide.  The  metals  of  the  fifth  and  sixth  groups  precipitate  in 
conjunction  with  free  sulphur  (§§  115  to  127),  the  chromic  acid  is 
reduced.  Filter  and  determine  the  chromium  in  the  filtrate,  as 
directed  in  I.,  a. 

ft.  Lead  chromate  may  be  conveniently  decomposed  by  heating 
with  hydrochloric  acid  and  some  alcohol ;  the  lead  chloride  and 
chromic  chloride  formed  are  subsequently  separated  by  means  of 
alcohol  (compare  §  162).  The  alcoholic  solution  ought  always  to  be 
tested  with  sulphuric  acid ;  should  a  precipitate  of  lead  sulphate 
form,  this  must  be  filtered  off,  weighed,  and  taken  into  account. 


*  Journ.  f.  prakt.  Chem.  77,  484. 

f  Proceedings  of  the  American  Academy,  5,  198. 


§  131.]  SELENIOUS   ACID.  361 

Supplement  to  the  First  Division. 

§131. 
1.  SELENIOUS  ACID. 

From  aqueous  or  hydrochloric  acid  solutions  of  selenious  acidr 
the  selenium  is  precipitated  by  sulphurous  acid  gas,  or,  in  presence 
of  an  excess  of  acid,  by  sodium  sulphite,  or  ammonium  sulphite. 
The  liquid  containing  the  precipitate  is  heated  to  boiling  for  J  hour, 
which  changes  the  precipitate  from  its  original  red  color  to  black, 
and  makes  it  dense  and  heavy.  The  liquid  is  tested  by  a  further 
addition  of  the  reagent  to  see  whether  any  more  selenium  will  sep- 
arate ;  the  precipitate  is  finally  collected  on  a  weighed  filter,  dried 
at  a  temperature  somewhat  below  100°,  and  weighed.  Since  H. 
ROSE*  has  shown  that  the  presence  of  hydrochloric  acid  is  an  essen- 
tial condition  to  the  complete  reduction  of  selenious  acid,  the  for- 
mer acid  must  be  added,  if  not  already  present.  To  make  quite 
sure  that  all  the  selenium  has  been  removed,  the  filtrate  is  evapo- 
rated to  a  small  volume,  with  addition  of  potassium  or  sodium  chlo- 
ride, boiled  with  strong  hydrochloric  acid,  so  as  to  reduce  any  sele- 
nic  acid  to  selenious  acid,  and  tested  once  more  with  sulphurous 
acid.  If  the  solution  contains  nitric  acid  it  must  be  evaporated 
repeatedly  with  hydrochloric  acid,  with  addition  of  sodium  or 
potassium  chloride.  If  the  latter  were  omitted  there  would  be 
considerable  loss  of  selenious  acid  (RATHKEf). 

As  regards  the  separation  of  selenious  acid  from  basic  radicals, 
the  following  brief  directions  will  suffice : 

a.  If  the  basic  radicals  are  not  liable  to  be  altered  by  the  action 
of  sulphurous  acid  and  hydrochloric  acid,  the  selenium  may  be  at 
once  precipitated  in  the  way  just  given ;  the  filtrate,  when  evap- 
orated with  sulphuric  acid,  yields  the  base  as  sulphate. 

b.  From  basic  metals  which  are  not  thrown  down  from  acid  solu- 
tion by  hydrogen  sulphide,  the  selenious  acid  may  be  separated  by 
precipitation  with  that  reagent.      The  precipitate  (according  to 
RATHKE^:,  a  mixture  of  SeS2,  Se2S  and  S)  contains  2  at.  sulphur  to 
1  at.  selenium.     If  it  is  dried  at  or  a  little  below  100°,  the  weight 


*  Zeitschr.  f.  anal.  Chem.  1,  73. 

f  Journ.  f.  prakt.  Chem.  108,  249;  Zeitschr.  f.  anal.  Chem.  9,  484. 

t  Journ.  f.  prakt.  Chem.  108,  252. 


362  DP:TERMINATIOIV.  [§  131. 

of  the  selenium  may  be  accurately  ascertained.  Should,  however, 
extra  sulphur  be  mixed  with  the  precipitate,  the  latter  is  oxidized 
while  still  moist  with  hydrochloric  acid  and  potassium  chlorate,  or 
by  treatment  with  potassa  solution  with  simultaneous  heating  and 
transmission  of  chlorine.  It  is  necessary  here  to  oxidize  the  sul- 
phur completely,  as  it  may  enclose  selenium,  The  solution  now 
containing  selenic  acid  is  heated  till  it  smells  no  longer  of  chlorine, 
hydrochloric  acid  is  added,  and  the  mixture  is  reheated.  The  sele- 
nic acid  is  hereby  reduced  to  selenious  acid,  and  when  the  solution 
has  again  ceased  to  smell  of  chlorine,  the  selenium  is  precip- 
itated with  sulphurous  acid.  Instead  of  this  process  you  may  digest 
the  precipitate  of  sulphur  and  selenium  for  some  hours  with  con- 
centrated potassium  cyanide,  which  will  completely  dissolve  it,  and 
then  throw  down  the  selenium  from  the  dilute  solution  with  hydro- 
chloric acid  as  in  c  (RATHKE,  loc.  cit.). 

c.  In  many  selenites  or  selenates  the  selenium  may  also  be 
determined  by  converting  first  into  potassium  selenocyanate,  and 
precipitating  the  aqueous  solution  of  the  latter  with  hydrochloric 
acid  (OppENHEiM*).  To  this  end  the  substance  is  mixed  with  7  or 
8  times  its  quantity  of  ordinary  potassium  cyanide  (containing 
cyanic  acid),  the  mixture  is  put  into  a  long-necked  flask,  or  a  porce- 
lain crucible,  covered  with  a  layer  of  potassium  cyanide,  and  fused 
in  a  stream  of  hydrogen.  The  temperature  is  kept  so  low  that 
the  glass  or  porcelain  is  not  attacked,  and  while  cooling  care  must 
be  taken  to  exclude  atmospheric  air.  When  cold,  the  brown  mass 
is  treated  with  water,  and  the  colorless  solution  filtered,  if  neces- 
sary. The  liquid  should  be  somewhat  but  not  immoderately 
diluted.  Now  boil  some  time  (in  order  to  convert  the  small  quan- 
tity of  potassium  selenide  that  may  be  present  into  potassium  sele- 
nocyanate, by  the  excess  of  potassium  cyanide,  allow  to  cool,  super- 
saturate with  hydrochloric  acid,  and  heat  again  for  some  time.  At 
the  end  of  12  or  24  hours  all  selenium  will  have  separated,  filter, 
dry  at  100°,  and  weigh.  The  results  obtained  by  this  process  are 
accurate  (H.  RosEf).  If  the  selenium  agglomerates  together  on 
heating,  it  may  enclose  salts.  In  such  cases,  by  way  of  control,  it 
should  be  redissolved  in  nitric  acid,  and,  after  addition  of  hydro- 
chloric acid,  precipitated  with  sulphurous  acid.  The  fluid  filtered 
from  the  selenium  precipitate  is,  as  a  rule,  free  from  selenium  ;  it 


Journ.  f.  prakt.  Chem.  71,  280.  f  Zeitschr.  f.  anal.  Chem.  1,  73. 


§  131.]  SULPHUROUS   ACID.  363 

is,  however,  always  well  to  satisfy  one's  self  on  this  point  by  the 
addition  of  sulphurous  acid. 

d.  From  many  basic  radicals  selenious  acid  (and  also  selenic 
acid)  may  be  separated  by  fusing  the  compound  with  2  parts  of 
sodium  carbonate  and  one  part  of  potassium  nitrate,  extracting  the 
fused  mass  thoroughly  by  boiling  with  water,  saturating  the  nitrate, 
if  necessary,  with  carbonic  acid,  to  free  it  from  lead  which  it  might 
contain,  then  boiling  down  with  hydrochloric  acid  in  excess  (to 
reduce  the  selenic  acid  and  drive  off  the  nitric  acid),  and  precipi- 
tating finally  with  sulphurous  acid. 

Selenium,  if  pure,  must  volatilize  without  residue  when  heated 
in  a  tube. 

2.  SULPHUROUS  ACID. 

To  estimate  free  sulphurous  acid  in  a  fluid  which  may  contain 
also  other  acids  (sulphuric  acid,  hydrochloric  acid,  acetic  acid),  a 
weighed  quantity  of  the  fluid  is  diluted  with  water,  absolutely  free 
from  air,*  until  the  diluted  liquid  contains  not  more  than  -05  per 
cent,  by  weight  of  sulphurous  acid,  the  solution  is  poured  with 
stirring  into  an  excess  of  standard  solution  of  iodine,  the  free 
iodine  remaining  is  titrated  with  sodium  thiosulphate,  and  the 
iodine  used  for  the  conversion  of  sulphurous  into  sulphuric  acid  is 
thus  found.  The  reaction  is  expressed  by  the  equation,  SO,  -f-  2H2 
O  +  21  =  H2SO4  +  2HI.  According  to  FINKENER,  if  the  iodine 
is  added  to  the  sulphurous  acid  the  reaction  is  not  quite  normal. 
Anyhow  this  method  of  operating  prevents  any  loss  of  sulphurous 
acid.  For  the  details,  see  §  146.  In  case  of  sulphites  soluble  in 
water  or  acids,  water  perfectly  free  from  air  is  poured  over  the 
substance,  in  sufficient  quantity  to  attain  the  degree  of  dilution 
stated  above,  sulphuric  or  hydrochloric  acid  is  added  in  excess,  and 
then  the  titration  is  effected  as  above.  The  greatest  care  must  be 
taken  in  this  method,  to  use,  for  the  purpose  of  dilution,  water 
absolutely  free  from  air. 

Sulphurous  acid  may  also  be  determined  in  the  gravimetric  way, 
by  conversion  into  sulphuric  acid,  and  precipitation  of  the  latter 
with  barium  chloride,  according  to  §  132.  This  method  is  espe- 
cially applicable  in  the  case  of  sulphites  quite  free  from  sulphuric 
acid.  The  conversion  of  the  sulphurous  into  sulphuric  acid  is 

*  Prepared  by  iQng-continued  boiling  and  subsequent  cooling  with  exclusion 
of  air. 


364  DETERMINATION.  [§  131. 

effected  in  the  wet  way,  best  by  pouring  the  dilute  solution  with 
stirring  into  excess  of  chlorine  or  bromine  water.  Sulphites  insolu- 
ble in  water  are  decomposed  by  boiling  with  sodium  carbonate,  and 
the  solution  of  sodium  sulphite  is  treated  as  directed.  After  driv- 
ing off  the  excess  of  chlorine  or  bromine  by  heating,  the  moderately 
acid  solution  is  precipitated  with  barium  chloride.  Sulphites  may 
be  oxidized  in  the  dry  way  by  heating  in  a  platinum  crucible,  with 
4  parts  of  a  mixture  of  equal  parts  sodium  carbonate  and  potassium 
nitrate. 

3.  THIOSULPHURIC  ACID. 

Thiosulphuric  acid,  in  form  of  soluble  thiosulphates,  may  be 
determined  by  means  of  iodine,  in  a  similar  way  to  sulphurous 
acid.  The  reaction  is  represented  by  the  equation,  2Na2S2O3  -f-  21 
=  2XaI  -f-  Na2S4O6.  The  salt  under  examination  is  dissolved  in  a 
large  amount  of  water,  starch-paste  added,  and  then  the  neutral 
solution  is  titrated  with  iodine.  That  this  method  can  give  correct 
results  only  in  cases  where  no  other  substances  acting  upon  iodine 
are  present,  need  hardly  be  mentioned.  Thiosulphuric  may  like 
sulphurous  acid  be  converted  into  sulphuric  acid  by  means  of  chlo- 
rine or  bromine  water,  and  then  determined. 

4.   IODIC  ACID. 

lodic  acid  may  be  determined  by  the  following  easy  method : — 
Distil  the  free  acid  or  iodate  with  an  excess  of  pure  fuming  hydro- 
chloric acid,  in  the  apparatus  described  in  §  1-30,6?,  ft  (chromic  acid), 
receive  the  disengaged  chlorine  in  solution  of  potassium  iodide,  and 
determine  the  separated  iodine  as  directed  in  §  130,  I,  d,  ft.  The 
decomposition  of  iodic  acid  by  hydrochloric  acid  is  represented  by 
the  equation,  H1O3  +  5HC1  =  IC1  +  4C1  +  3H2O.  Since  the  4 
at.  Cl  set  free  4  at.  I,  the  amount  of  iodic  acid  or  iodic  anhydride 
can  be  calculated  from  the  weight  of  the  latter  ;  1014-8  iodine  cor- 
respond to  333-7  iodic  anhydride  (IQO5)  (BUNSEN*).  The  following 
method  also  yields  good  results.  Mix  the  solution  with  dilute  sul- 
phuric acid,  add  potassium  iodide  in  excess,  and  determine  the 
amount  of  liberated  iodine,  after  §  146.  One  sixth  of  the  iodine 
thus  formed  is  derived  from  the  iodic  acid  (HIO3  +  5HI  =  3H2O 

+  I6).        See  RAMMELSBERG.f 


*  Annal.  d.  Chem.  u.  Pharm.  86,  285. 

f  Pogg.  Annal.  135,  493  ;  Zeitschr.  f.  anal.  Chem.  8,  456. 


§  131.]  NITROUS    ACID.  365 

5.  NITROUS  ACID. 

The  nitrous  acid  in  nitrites  which  are  free  from  nitrates  may 
be  estimated  by  converting  the  nitrogen  into  ammonia  and  deter- 
mining the  latter,  or  by  determining  the  oxidizing  action  on  ferrous 
salt.  This  method  is  conducted  exactly  as  described  under  nitric 
acid  (§  149).  When  nitric  acid  is  also  present,  nitrous  acid  may  be 
determined  very  satisfactorily  with  a  solution  of  pure  potassium 
permanganate,  provided  the  fluid  be  sufficiently  diluted  to  prevent 
the  nitrous  acid,  which  is  liberated  by  the  addition  of  a  stronger 
acid,  being  decomposed  by  water  with  formation  of  nitric  acid 
and  nitric  oxide.  For  1  part  of  nitrous  anhydride  at  least  5000 
parts  of  water  should  be  present.  The  decomposition  is  repre- 
sented by  the  following  equation,  5HNO,  -f-  K,Mn,O8  -f-  3H,SO4 
=  5HNO3+K2SO4  +  2MnSO4  +  3H,O.  If  the  permanganate 
be  standardized  with  iron,  4  at.  iron  correspond  to  1  raol.  N2O3, 
since  both  of  these  require  2  at.  oxygen.  Nitrites  are  dissolved  in 
very  slightly  acidulated  water,  the  permanganate  is  added  till  the 
oxidation  of  the  nitrous  acid  is  nearly  completed,  the  solution  is 
then  made  strongly  acid,  and  finally  permanganate  is  added  to  ligl  it- 
red  coloration. 

To  determine  nitrogen  tetroxide  N,O4  in  red  fuming  nitric  acid, 
transfer  a  few  c.c.  to  about  500  c.c.  cold  pure  distilled  water  with 
stirring,  and  determine  the  nitrous  acid  produced.  1  mol.  nitrous 
anhydride  found  corresponds  to  2  mol.  nitrogen  tetroxide,  for  the 
latter  —  when  mixed  with  such  a  large  quantity  of  water  as  is  indi- 
cated above  —  is  decomposed  in  accordance  with  the  following  equa- 
tion :—  NaO4  +  H2O  =  HNO3  +  HNO,  (Sio.  FELDHAUS*). 

Nitrous  acid  and  nitrogen  tetroxide  in  presence  of  nitric  acid 
may  also  be  estimated  by  the  reduction  of  chromic  acid.  An 
excess  of  standard  potassium  dichromate  is  added,  and  the  unde- 
composed  residue  of  chromic  acid  is  estimated  with  standard  solu- 
tion of  ferrous  salt  (F.  MoHRf). 

As  regards  the  estimation  of  nitrous  acid  with  lead  dioxide, 
comp.  FELDHAUS,  loc.  tit.  p.  431,  also  LANG^:  and  J.  LOWENTHAL.§ 


*  Zeitschr.  f.  anal.  Chem.  1,  426. 

f  His  Lehrbuch  der  Titrirmethode.  3  Aufl.  236. 

\  Zeitschr.  f.  anal.  Chem.  1,  485.  §  Ib.  3,  176. 


366  DETEBMIKATIO]*.  [§  132. 

Second  Division  of  the  First  Group  of  the  Acids. 
SULPHURIC  ACID  ;  (Hydrofluosilicic  Acid). 

§  132. 
SULPHURIC  ACID. 

I.  DETERMINATION. 

Sulphuric  acid  is  usually  determined  in  the  gravimetric  way  as 
barium  sulphate.  The  acid  may,  however,  be  estimated  also  by 
the  acidimetric  method  (§  192),  and  by  certain  volumetric  methods, 
based  upon  the  insolubility  of  the  barium  sulphate  (and  lead  sul- 
phate). 

1.  Gravimetric  Method. 

The  exact  estimation  of  sulphuric  acid  as  barium  sulphate  is  by 
no  means  so  simple  and  easy  as  it  was  formerly  supposed  to  be,  but 
requires,  on  the  contrary,  great  care  and  attention.  This  arises 
from  three  causes :  first,  the  barium  sulphate  is  found  to  be  far 
more  soluble  than  was  imagined  in  solutions  of  free  acids  and  of 
many  salts ;  secondly,  it  is  extremely  liable  to  carry  down  with  it 
foreign  salts,  which  are  of  themselves  soluble  in  water ;  thirdly, 
when  the  precipitate  has  once  separated  in  an  impure  state,  it  is 
often  very  difficult  to  purify  it  completely. 

The  solution  should  contain  but  little  free  hydrochloric  acid, 
and  no  nitric  or  chloric  acid.  If  either  of  the  two  last  are  present, 
evaporate  repeatedly,  on  the  water-bath  with  pure  hydrochloric 
acid.  Dilute  considerably,  heat  nearly  to  boiling,  add  barium  chlo- 
ride in  moderate  excess,  and  allow  to  settle  for  a  long  time  at  a 
gentle  heat.  Decant  the  clear  fluid  through  a  filter,  treat  the  pre- 
cipitate with  boiling  water,  allow  to  settle,  decant  again,  and  so  on, 
till  the  washings  are  free  from  chlorine.  Finally  transfer  the  pre- 
cipitate to  the  filter,  dry  and  treat  according  to  §  53,  using  only  a 
moderate  red  heat. 

After  the  precipitate  has  been  weighed  it  is  well  to  warm  it  for 
some  time  with  dilute  hydrochloric  acid  on  the  water-bath.  Then 
pour  off  the  hydrochloric  acid  through  a  small  filter,  wash  the  pre- 
cipitate by  decantation  with  boiling  water  without  removing  it  to 
the  filter,  evaporate  the  filtrate  and  washings  nearly  to  dry  ness  in 
a  platinum  or  porcelain  dish,  add  water,  collect  the  minute  amount 


§  132.]  SULPHURIC   ACID.  367 

of  barium  sulphate  here  left  undissolved  upon  the  small  filter, 
wash,  dry,  incinerate,  add  the  ash  to  the  bulk  of  the  precipitate, 
ignite  again,  and  weigh.  If  the  precipitate  has  lost  weight,  this 
shows  that  it  at  first  contained  foreign  salts. 

This  method  of  purification  sometimes  fails  when  the  precipi- 
tate contains  ferric  oxide  or  platinum  (CLAUS*),  and  it  invariably 
fails  when  the  solution  contained  any  notable  quantity  of  nitric 
acid.t  In  such  cases  there  is  only  one  resource,  namely,  to  fuse 
with  about  four  parts  of  sodium  carbonate,  warm  with  water,  filter, 
wash  with  boiling  water,  acidify  the  filtrate  slightly  with  hydro- 
chloric acid,  and  determine  the  sulphuric  acid  again. 

The  results  are  thoroughly  satisfactory  if  these  directions  are 
attended  to ;  if  not,  the  result  may  be  two  or  three  per  cent,  too 
high  or  too  low. 

2.  Volumetric  Methods. 

a.  After  CARL  MOHK.;):  We  require  a  normal  solution  of 
barium  chloride,  containing  121*96  grm.  of  the  pure  crystallized 
salt  in  1  litre,  and  also  normal  nitric  or  hydrochloric  acid  and 
normal  soda  (§  192,  c.  6).  Add  to  the  fluid  to  be  examined  for 
sulphuric  acid — which,  should  it  contain  much  free  acid,  is  previ- 
ously to  be  nearly  neutralized  with  pure  sodium  carbonate — a  meas- 
ured quantity  of  barium  chloride  solution,  best  a  round  number 
of  cubic  centimetres,  in  more  than  sufficient  proportion  to  precipi- 
tate the  sulphuric  acid,  but  not  in  too  great  excess.  Digest  the 
mixture  for  some  time  in  a  warm  place,  then  precipitate,  without 
previous  filtration,  the  excess  of  barium  chloride  with  ammonium 
carbonate  and  a  little  ammonia,  filter  off  the  barium  sulphate  and 
carbonate,  wash  until  the  water  running  off  acts  no  longer  upon 
red  litmus  paper,  and  then  determine  the  barium  carbonate  by  the 
alkaliinetric  method  given  in  §  198.  Deduct  the  c.c.  of  normal 
acid  used  from  the  c.c.  of  barium  chloride,  and  the  remainder  will 
be  the  c.c.  of  barium  chloride  corresponding  to  the  sulphuric  acid 
present.  The  results  of  this  method  are  quite  satisfactory,  if  the 
solution  does  not  contain  too  much  free  acid ;  but  in  presence  of  a 
large  excess  of  free  acid,  the  action  of  the  salt  of  ammonia  will 
retain  barium  carbonate  in  solution,  which,  of  course,  will  make 

*  Jahresber.  von  KOPP  und  WILL.  1861,  323,  note, 
f  Compare  my  paper  in  Zeitschr.  f.  anal.  Chem.  9,  52. 
j  Ann.  der  Chem.  u.  Pharm.  90,  165. 


368  DETERMINATION.  [§  132. 

the  amount  of  sulphuric  acid  appear  higher  than  is  really  the  case. 
It  need  hardly  be  mentioned  that  this  method  is  altogether  inap- 
plicable in  presence  of  phosphoric  acid,  oxalic  acid,  or  any  other 
acid  precipitating  barium  salt  from  neutral  solutions,  and  that  no 
basic  radicals  except  the  alkalies  may  be  present. 

b.  After  R.  WILDENSTEIN.*  Of  all  the  methods  for  the  volu- 
metric estimation  of  sulphuric  acid,  the  simplest  and  that  which  is 
capable  of  the  most  general  application,  is  to  drop  into  the  solution 
containing  excess  of  hydrochloric  acid,  standard  barium  chloride 
solution,  till  the  exact  point  is  reached  when  no 
more  precipitation  takes  place.  This  point  is  diffi- 
cult to  hit,  and  hence  the  method  has  only  found  a 
very  limited  use. 

"WILDENSTEIN  has  given  this  method  a  practical 
form,  which  renders  it  possible  to  complete  an 
analysis  in  about  half  an  hour,  and  at  the  same  time 
to  obtain  satisfactory  results.  He  employs  the  ap- 
paratus, fig.  56.  A  is  a  bottle  of  white  glass,  whose 
bottom  has  been  removed,  it  contains  900 — 950  c.c. 
B  is  a  strong  funnel-tube,  with  bell-shaped  funnel,  Flg-  56* 
and  bent  as  shown,  provided  below  with  a  piece  of  india-rubber 
tube,  a  screw  compression-cock,  and  a  small  piece  of  tubing  not 
drawn  out,  The  length  from  c  to  d  is  about  7-J-8,  from  d  to  e 
about  12  cm.  The  opening  of  the  funnel-tube  /",  which  should 
have  a  diameter  of  2'5  to  3  crn.,  is  covered  as  follows :  Take  a 
piece  of  fine  new  calico  or  muslin,  free  from  sulphuric  acid,  and 
about  6  cm.  square,  lay  on  it  two  pieces  of  Swedish  paper  of  the 
same  size,  and  then  another  piece  of  stuff  like  the  first,  now  bind 
these  altogether  over  the  opening/1,  carefully  and  without  injuring 
the  paper,  by  means  of  a  strong  linen  thread  which  has  been  drawn 
a  few  times  over  wax,  and  cut  it  off  even  all  round.  We  have 
now  a  small  syphon-filter,  which  enables  us  to  filter  off  a  portion 
of  fluid  contained  in  A,  and  turbid  from  barium  sulphate,  clear 
and  with  comparative  rapidity. 

On  gradually  adding  barium  chloride  to  the  dilute  acid  solution 
of  a  sulphate  a  point  occurs  which  may  be  compared  to  the  neutral 
point  in  precipitating  silver  with  sodium  chloride  (see  §  115,  5, 5.) ; 
£.<?.,  there  is  a  certain  moment,  when  a  portion  filtered  off  will  give 


*  Zeitschr.  f.  anal.  Chem.  1, 


§  132.]  SULPHURIC   ACID.  369 

a  turbidity  both  with  sulphuric  acid  and  barium  chloride  after  the 
lapse  of  a  few  minutes.  On  this  account  we  must  either  proceed 
on  the  principle  recommended  for  the  estimation  of  silver,  i.e.,  dis- 
regarding the  quantity  of  barium  chloride  in  the  solution,  to  stand- 
ardize it  by  adding  it  to  a  known  amount  of  sulphate,  till  a  pre- 
cipitate ceases  to  be  formed  ;  or  else  we  must — and  WILDENSTEIX 
recommends  this  latter  course — consider  as  the  end-point  of  the 
reaction  the  point  at  which  barium  chloride  ceases  to  produce  a 
distinctly  visible  precipitation  in  the  clear  filtrate  after  a  lapse  of 
two  minutes. 

The  barium  chloride  solution  is  prepared  so  that  1  c.c.  corre- 
sponds to  '02  sulphuric  anhydride  by  making  a  solution  containing 
the  requisite  calculated  and  carefully  weighed  amount  of  the  pure 
salt  per  litre. — A  solution  of  sulphuric  acid  containing  '02  gr.  SO, 
per  c.c.  may  also  be  required.  The  process  is  as  follows : 

First  prepare  the  solution  of  the  sulphate  to  be  analyzed  (using 
about  3  or  4  gnu.),  then  fill  A  with  hot  water,  open  the  cock  with 
the  screw  or  by  the  aid  of  a  glass  rod,  and  wait  till  the  syphon  B 
is  quite  full  of  water.  If  the  water  runs  down  the  tube  c  e  with- 
out filling  it  entirely,  close  and  open  the  cock  a  few  times,  and  this 
inconvenience  will  be  removed.  (It  is  not  allowable  to  suck  at  0, 
or  to  fill  the  syphon  with  the  wash-bottle  at  ey  as  either  proceeding 
would  inevitably  lead  to  injuring  the  filter.)  Now  close  the  cock 
and  pour  out  the  hot  water,  replace  it  by  400  c.c.  of  boiling  water, 
add  the  ready-prepared  solution  of  the  sulphate,  and  a  small  quan- 
tity of  hydrochloric  acid,  if  necessary,  and  run  in  the  barium  chlo- 
ride solution,  at  first  in  rather  large  portions,  at  last  in  J  c.c. 
Before  each  fresh  addition  of  barium  chloride  open  the  cock  and 
allow  rather  more  liquid  to  flow  into  a  beaker  than  corresponds  to 
the  contents  of  the  syphon.  This  quantity  should  be  previously 
ascertained,  and  a  mark  indicating  it  made  on  the  beaker.  Now 
close  the  cock  and  pour  the  filtrate  without  loss  back  into  A.  (As 
the  beaker  is  used  over  and  over  again  for  the  same  purpose,  it 
need  not  be  rinsed  out.)  Now  run  some  of  the  fluid  into  a  test- 
tube,  so  as  to  one  third  fill  it,  add  to  the  clear  fluid  2  drops  of 
barium  chloride  from  the  burette  and  shake.  If  a  precipitate  or 
turbidity  is  produced,  return  the  portion  to  the  main  quantity.  The 
experiment  is  finished  when  the  last  portion  tested  shows  after  the 
lapse  of  exactly  two  minutes  no  distinctly  visible  turbidity.  The 
drops  of  barium  chloride  used  for  the  last  testing  are  of  course  not 


370  DETERMINATION.  [§  132. 

reckoned.  The  slight  error  involved  from  the  fact  that  the  small 
quantity  of  fluid  in  the  syphon  is  finally  unacted  on,  is  too  small 
to  be  noticed.  During  the  experiment  the  filter  must  not  be 
injured  by  the  stirring.  In  case  the  end  reaction  has  been  over- 
stepped, add  1  c.c.  of  dilute  sulphuric  acid  (equivalent  to  the  barium 
chloride)  to  A,  and  endeavor  to  hit  it  again.  Here  1  c.c.  will 
have  to  be  subtracted  from  the  c.c.  of  barium  chloride  used. 

The  results  obtained  by  WILDENSTEIN  are  of  sufficient  accuracy 
for  technical  purposes.  Some  experiments  made  in  my  own  labo- 
ratory were  also  quite  satisfactory. 

II.  SEPARATION  OF  SULPHURIC  ACID  FROM  THE  BASIC 
RADICALS. 

a.  In  Sulphates  which  are  soluble  in  Water  or  Hydrochloric 
Acid. 

The  solution  should  be  free  from  nitric  acid.  Precipitate  the 
sulphuric  acid  according  to  I.  by  barium  chloride  (or  barium  ace- 
tate). The  filtrate  contains  the  excess  of  barium  chloride,  together 
with  the  chlorides  of  the  metals  present ;  separate  barium  from  the 
latter  by  methods  given  in  the  fifth  section.  The  fluid  obtained  by 
treating  the  ignited  barium  sulphate  with  hydrochloric  acid,  evap- 
orating and  filtering  from  the  small  amount  of  barium  sulphate, 
must  be  added  to  the  first  solution  before  separating  barium  from  it. 

b.  In  /Sulphates   which  are  insoluble  or  difficultly  soluble   in 
Water  or  in  Hydrochloric  Acid. 

a.  From  barium,  strontium  and  calcium :  Fuse  the  finely  pul- 
verized substance  in  a  platinum  crucible,  with  5  parts  of  mixed 
sodium  and  potassium  carbonates.  Put  the  crucible,  with  its  con- 
tents, into  a  beaker,  or  into  a  platinum  or  porcelain  dish,  pour 
water  over  it,  and  apply  heat  until  the  alkali  sulphates  and  carbon- 
ates are  completely  dissolved  ;  filter  the  hot  solution  from  the  resid- 
uary alkali-earth  carbonates,  wash  the  latter  thoroughly  with  water, 
to  which  a  little  ammonia  and  ammonium  carbonate  has  been  added, 
and  determine  according  to  §§  101  to  103.  If  the  precipitates  have 
been  well  washed,  it  is  perfectly  admissible  to  ignite  and  weigh  at 
once.  Precipitate  the  sulphuric  acid  from  the  filtrate,  as  in  L, 
after  acidifying  with  hydrochloric  acid.  Finely  pulverized  calcium 
and  strontium  sulphates  may  be  completely  decomposed  also  by 
boiling  with  a  solution  of  potassium  carbonate.* 

*  Sodium  carbonate  does  not  answer  as  well. 


§132.]  sruMi URIC  ACID.  371 

ft.  From  lead :  The  simplest  way  of  effecting  the  decomposi- 
tion of  lead  sulphate  consists  in  digesting  it,  at  the  common  tem- 
perature, with  a  solution  of  hydrogen  sodium  or  hydrogen  potas- 
sium carbonate,  filtering,  washing  the  precipitate,  determining  the 
sulphuric  acid  in  the  filtrate  as  in  I.,  dissolving  the  precipitate, 
which  contains  alkali,  in  nitric  or  acetic  acid,  and  determining  the 
lead  in  the  solution,  by  one  of  the  methods  given  in  §  162. 

Presence  of  strontium  and  calcium  necessitates  no  alteration  in 
this  method ;  but  if  barium  also  is  present,  and  it  is  accordingly 
necessary  to  ignite*  the  mixture  with  alkali  carbonates,  a  small 
portion  of  lead  always  remains  in  solution  in  the  alkaline  fluid  ;  this 
must  be  precipitated  by  passing  through  it  carbon  dioxide  before 
filtering. 

y.  From  mercury  in  mercurous  sulphate :  Mercurous  sulphate 
is  best  dissolved  by  warming  with  dilute  hydrochloric  acid  with 
addition  of  potassium  chlorate  or  bromine,  and  the  solution  is 
treated  according  to  a.  If  the  salt  is  boiled  with  solution  of  potas- 
sium carbonate,  the  mercurous  carbonate  first  formed  is  decom- 
posed, and  the  residue  contains  metallic  mercury  and  mercuric 
oxide ;  a  small  part  of  the  latter  passes  into  the  filtrate. 

III.    ESTIMATION    OF  FREE  SULPHURIC  ACID    IN  PRES- 
ENCE OF  SULPHATES. 

We  have  occasionally  to  estimate  the  free  acid  in  presence  of 
sulphates,  as,  for  instance,  in  vinegar,  wine,  etc.  According  to  A. 
GiRARDf  the  following  is  the  only  direct  method  which  can  be 
relied  on.  Evaporate  on  the  water-bath  to  dryness  and  exhaust  the 
residue  with  absolute  alcohol ;  determine  the  combined  acid  in  the 
residue,  and  the  free  acid  in  the  alcoholic  extract,  after  mixing  with 
water  and  evaporating  off  the  alcohol.  It  has  been  said  that  the 
object  may  be  obtained  by  the  use  of  barium  carbonate,  which  is 
supposed  to  throw  down  the  free  acid  only,  but  this  is  erroneous, 
since  alkali  sulphates  in  aqueous  solution  are  partially  decomposed 
at  the  ordinary  temperature  by  barium  carbonate.  In  some  cases 
the  amount  of  free  sulphuric  acid  present  may  be  calculated  after 
having  determined  the  total  amount  of  basic  and  acid  radicals 
present.  When  no  other  free  acid  is  present,  free  sulphuric  acid 
may  be  determined  by  the  acidimetric  process. 

*  This  is  best  done  in  a  porcelain  crucible. 

f  Compt.  rend.  58,  515;  Zeitschr.  f.  anal.   Chem.  4,  219. 


372  DETERMINATION.  [§  138. 

Supplement  to  the  Second  Division. 

§  133. 
HYDROFLUOSILICIC  ACID. 

If  you  have  hydrofluosilicic  acid  in  solution,  add  solution  of 
potassium  chloride,  then  a  volume  of  strong  alcohol  equal  to  the 
fluid  present,  collect  the  precipitated  potassium  silicofluoride  on  a 
weighed  filter,  jand  wash  with  a  mixture  of  equal  volumes  of  alco- 
hol and  water.  Dry  the  washed  precipitate  at  100°,  and  weigh. 
Mix  the  alcoholic  filtrate  with  hydrochloric  acid,  evaporate  to  dry- 
iiess,  and  treat  the  residue  with  hydrochloric  acid  and  water.  If 
this  leaves  an  undissolved  residue  of  silicic  acid,  this  is  a  sign  that 
the  examined  acid  contained  an  excess  of  silicic  acid  ;  the  weight 
of  the  residue  shows  the  amount  of  excess.  Potassium  silicofluor- 
ide dried  at  100°  has  the  formula  (K  F)a  SiF4 ;  for  its  properties, 
see  §  68.  Instead  of  weighing  it,  it  may  be  estimated  volumetric- 
ally  according  to  §  97,  4.  The  analysis  of  metallic  silicofluorides  is 
I  >est  effected  by  heating  in  platinum  vessels,  with  concentrated  sul- 
phuric acid ;  silicon  fluoride  and  hydrofluoric  acid  volatilize,  the  basic 
metals  are  left  behind  in  the  form  of  sulphates,  and  may,  in  many 
cases,  after  volatilization  of  the  excess  of  sulphuric  acid,  be  weighed 
:us  such.  If  the  metallic  silicofluorides  to  be  analyzed  contain  water, 
the  latter  cannot  be  estimated  by  mere  ignition,  since  silicon  fluoride 
would  escape  with  the  water.  II.  ROSE  recommends  the  following 
method :  Mix  them  most  intimately  with  6  parts  of  recently  ignited 
lead  oxide,  cover  the  mixture  in  a  small  retort,  with  a  layer  of 
pure  lead  oxide,  weigh  the  retort,  heat  cautiously  until  the  contents 
begin  to  fuse  together,  remove  the  aqueous  vapor  still  remaining 
in  the  vessel  by  suction,  and  weigh  the  retort  again  when  cold. 
The  diminution  of  weight  shows  the  quantity  of  water  expelled. 
Do  not  neglect  testing  the  drops  of  the  escaping  water  with 
litmus  paper;  the  result  is  accurate  only  if  they  have  no  acid 
reaction. 

F.  STOLBA*  proposes  the  following  process,  at  least  for  com- 
pounds soluble  in  water :  Put  into  a  crucible  double  as  much  inag- 
riesia  as  is  necessary  to  decompose  the  silicofluoride  to  be  analyzed, 
ignite  it  as  strongly  as  possible,  allow  to  cool,  and  weigh.  Add  water 

*  Zeitschr.  f .  anal.  Chem.  7,  93. 


§  134.]  PHOSPHORIC   ACID.  373 

to  form  a  thick  paste,  and  then  the  weighed  silicofluoride ;  if  the 
amount  of  water  present  is  not  enough  to  dissolve  the  compound, 
add  some  more,  mix  with  a  platinum  wire  which  must  afterwards 
be  wiped  off  clean,  dry,  ignite,  and  weigh.  The  increase  in  weight 
shows  the  amount  of  anhydrous  silicofluoride,  provided  no  oxide  is 
present  which  takes  up  oxygen. 


Third  Division  of  the  First  Group  of  the  Acids. 

PHOSPHORIC    ACID BORACIC   ACID OXALIC   ACID HYDROFLUORIC 

ACID. 

§  134. 

1.  PHOSPHORIC  ACID. 

I.  DETERMINATION. 

Orthophosphoric  acid  may  be  determined  in  a  great  variety  of 
ways.  The  forms  in  which  this  determination  may  be  effected 
have  been  given  already  in  §  93,  4.  The  most  appropriate  forms 
for  the  purpose,  however,  are  magnesium  pyrophosphate  and  ura- 
nyl  pyrophosphate.  The  determination  as  magnesium  pyrophos- 
phate is  frequently  preceded  by  precipitation  in  another  way, 
especially  as  ammonium  phospho-molybdate,  occasionally  as  stannic 
phosphate  or  mercurous  phosphate.  The  other  forms  in  which 
phosphoric  acid  may  be  determined  give  also,  in  part,  very  good 
results,  but  admit  only  of  a  more  limited  application.  With 
respect  to  volumetric  methods,  those  which  depend  upon  the  use 
of  standard  solution  of  uranium  are  the  best. 

With  regard  to  meta-  and  pyrophosphoric  acids,  I  have  simply 
to  remark  here  that  these  acids  cannot  be  determined  by  any  of  the 
methods  given  below.  The  best  way  to  effect  their  determination 
is  to  convert  them  into  orthophosporic  acid,  as  follows : 

a.  In  the  dry  way.  By  protracted  fusion  with  from  4  to  6 
parts  of  mixed  sodium  and  potassium  carbonates.  This  method  is, 
however,  applicable  only  in  the  case  of  alkali  meta-  and  pyrophos- 
phates,  and  of  those  metallic  meta-  or  pyrophosphates  which  are 
completely  decomposed  by  fusion  with  alkali  carbonates  ;  it  fails, 
accordingly,  for  instance,  with  the  salts  of  the  alkali-earth  metals, 
magnesium  excepted. 

ft.  In  the  ivet  way.     The  salt  is  heated  for  some  time  with  a 


374  DETERMINATION.  [§  134. 

strong  acid,  best  with  concentrated  sulphuric  acid  (WEBER*).  This 
method  leads  only  to  the  attainment  of  approximate  results,  in  the 
case  of  all  salts  whose  basic  radicals  form  soluble  salts  of  the  acid 
added,  since  in  these  cases  the  meta-  or  pyrophosphoric  acid  is 
never  completely  liberated  ;  but  the  desired  result  may  be  fully 
attained  by  the  use  of  any  acid  which  forms  insoluble  salts  compounds 
with  the  basic  radicals  present.  Respecting  the  partial  conversion 
in  the  former  case,  I  bave  found  that  it  approaches  the  nearer  to 
completeness  the  greater  the  quantity  of  free  acid  added,f  and  that 
the  ebullition  must  be  long  continued. 

BUNCE'S  statement,^  that  phosphoric  acid  volatilizes  when  a 
phosphate  is  evaporated  to  dryness  with  hydrochloric  or  nitric  acid 
and  the  residue  heated  a  little,  is  quite  erroneous  (compare  my 
paper  on  the  subject,  in  Annal.  der  Chem.  und  Pharm.,  86,  216). 
But,  on  the  other  hand,  it  must  be  borne  in  mind  that;  orthophos- 
phoric  acid  under  these  circumstances  changes,  not  indeed  at  100°, 
but  at  a  temperature  still  below  150°,  to  pyrophosphoric  acid  ;  thus, 
for  instance,  upon  evaporating  common  hydrogen  sodium  phos- 
phate with  hydrochloric  acid  in  excess,  and  drying  the  residue  at 
150°,  we  obtain  2  Nad  +  Na2H2P2O7. 

a.  Determination  as  Lead  Phosphate. 

Proceed  as  with  arsenic  acid,  §  127,  1,  a — ?>.,  evaporate  with 
a  weighed  quantity  of  oxide  of  lead,  and  ignite.  This  method  pre- 
supposes that  no  other  acid  'is  present  in  the  aqueous  or  nitric  acid 
solution;  it  has  this  great  advantage,  that  it  gives  correct  results, 
no  matter  whether  ortho-,  meta-,  or  pyrophosphoric  acid  is  present. 

b.  Determination  as  Magnesium  Pyrophosphate. 

of.  Direct  determination.  Suitable  in  all  cases  in  which  it  is 
quite  certain  that  the  acid  present  is  orthophosphorie,  either  free 
or  combined  as  an  alkali  phosphate. 

The  solution  should  be  neutral,  or  only  moderately  ammoniacal. 
Add  ammonium  chloride,  and  then  the  usual  magnesia  mixture 
(§  62,  6),  in  sufficient  but  not  too  excessive  quantity  (see  §  62,  6). 
The  precipitate  being  under  these  conditions  somewhat  slowly 
formed,  appears  distinctly  crystalline.  After  some  time  add  am- 
monia gradually  to  the  amount  of  one  third  of  the  fluid.  Allow 


*  Pogg.  Anna!.  73,  137. 

f  There  are,  however,  other  considerations  which  forbid  going  too  far  in  this 
respect,  $  Sillim.  .Tourn.  May,  1851.  405. 


§  134.]  PHOSPHORIC   ACID.  375 

to  stand  12  hours  in  a  well-covered  vessel  in  the  cold,  filter,  test 
the  filtrate  with  magnesia  mixture  and  ammonia,  and  wash  the  pre- 
cipitate with  ammonia  diluted  with  3  volumes  of  water  till  the 
washings,  when  acidified  with  nitric  acid  and  tested  with  silver 
nitrate,  are  no  longer  rendered  turbid  ;  proceed  according  to  §  104, 
2.  The  precipitate  is  not  absolutely  insoluble  in  ammoniated 
water,  therefore  it  is  well  to  wash  by  suction,  as  this  reduces  the 
necessary  amount  of  wash  water  to  a  minimum.  The  results  are 
accurate  (Expt.  No.  89,  also  KISSEL*).  If  there  is  reason  to  sus- 
pect the  purity  of  the  precipitate,  dissolve  it  in  hydrochloric  acid, 
and  throw  down  again  with  ammonia,  adding  some  magnesia 
mixture.  If  the  magnesia  mixture  is  omitted,  the  solution  being 
free  from  magnesia  will  dissolve  some  of  the  precipitate.  Com- 
pare KISSEL,  loc.  cit.  Properties  of  the  precipitate  and  residue, 
§  74.  If  the  solution  contains  pyrophosphoric  acid,  the  precipi- 
tate is  flocculent  and  dissolves  to  a  notable  degree  in  ammoniated 
water  (WEBER). 

ft.  Indirect  determination,  with  previous  precipitation  as  arfnno- 
nium  phosphomolybdate,  after  SoiorENSCHEiN.f 

Applicable  in  all  cases  in  which  the  phosphoric  acid  present  is 
orthophosphoric,  even  in  presence  of  salts  of  the  alkali-earth  metals, 
aluminium,  ferric  iron,  &c.  Tartaric  acid,  however,  and  similar!  v 
acting  organic  substances  must  be  absent.  No  considerable  quan- 
tity of  free  hydrochloric  acid  may  be  present.  Large  quantities  of 
ammonium  chloride,  and  of  metallic  chlorides  generally,  also  of 
certain  ammonium  salts,  especially  the  oxalate  and  citrate  (KoNiG)J, 
are  to  be  avoided.  Ammonium  nitrate  assists  the  precipitation  and 
neutralizes  the  injurious  action  of  very  large  quantities  of  nitrates 
and  sulphates  (E.  RICHTERS)§.  The  molybdenum  solution  described 
u  Qual.  Anal.,"  §  55,  is  employed  as  the  precipitant.  It  contains  5 
per  cent,  of  molybdic  acid.  The  fluid  to  be  examined  for  phos- 
phoric acid  should  be  concentrated,  it  may  contain  free  nitric  or 
free  sulphuric  acid.  Transfer  to  a  beaker  and  add  a  considerable 
quantity  of  the  molybdenum  solution.  About  40  parts  molybdic 
acid  must  be  added  for  every  1  part  phosphoric  anhydride,  there- 
fore 80  c.c.  of  the  molybdic  solution  for  -1  grm.  Stir,  without 
touching  the  sides,  and  keep  covered  12  hours  at  about  40°.  Then 
remove  a  portion  of  the  clear  supernatant  fluid  with  a  pipette,  mix 

*  Zeitschr.  f.  anal.  Chem.  8,  170.  \  Journ.  f.  prakt.  Chem.  53,  343. 

\  Zeitschr.  f .  anal.  Chem.  10,  305.          §  Ib.  10,  4G9. 


376  DETERMINATION.  [§  134. 

it  with  an  equal  volume  of  molybdenum  solution,  and  allow  it  to 
stand  some  time  at  40°.  If  a  further  precipitation  takes  place, 
return  the  portion  to  the  main  quantity,  add  more  molybdenum 
solution,  allow  to  stand  again  12  hours,  and  test  again.  When 
complete  precipitation  has  been  effected  pour  the  fluid  off  through 
a  small  filter  and  wash  the  precipitate  entirely  by  decantation, 
using  a  mixture  of  100  parts  molybdate,  solution,  20  parts  nitric 
acid  of  1'2  sp.  gr.,  and  80  parts  water.*  The  washing  must  be 
thorough,  and  the  last  runnings  must  not  be  precipitated  by  excess 
of  ammonia,  even  if  lime,  iron,  &c.,  was  present  in  the  solution. 
Now  dissolve  the  precipitate  in  the  least  quantity  of  ammonia, 
pour  the  fluid  through  the  small  filter,  when  the  minute  amount  of 
precipitate  thereon  will  be  dissolved,  wash  the  filter  with  ammonia 
diluted  with  three  volumes  of  water,  mix  the  filtrate  and  washings, 
and  add  hydrochloric  acid  carefully  till  the  precipitate  produced, 
instead  of  redissolving  instantly,  takes  a  little  time  to  disappear ; 
finally  throw  down  with  magnesia  mixture  (compare  a).  If  the 
ammonia  leaves  a  small  amount  of  the  precipitate  undissolved, 
treat  the  residue  with  nitric  acid  and  test  the  filtrate  with  molybdic 
solution  in  order  to  save  any  phosphoric  acid.  Results  accurate.f 
As  this  method  requires  so  large  a  quantity  of  molybdic  acid,  it 
is  usually  resorted  to  only  in  cases  where  methods  &,  a,  and  c  are 
inapplicable  ;  and  the  phosphoric  acid  in  the  quantity  of  substance 
taken  is  not  allowed  to  exceed  '3  grm.  Arsenic  acid  and  silicic 
acid,;):  if  present,  must  first  be  removed.  Of  all  the  methods  for 
determining  phosphoric  acid  which  are  admissible  in  the  presence 
of  ferric  and  aluminium  salts,  this  is  the  best  in  my  opinion,  espe- 
cially for  the  estimation  of  small  quantities  of  the  acid  in  presence 
of  large  quantities  of  these  salts. 

*  According  to  E.  RICHTERS  (Zeitschr.  f.  anal.  Chem.  10,  471)  you  may  also 
wash  with  a  solution  of  ammonium  nitrate  containing  15  grm.  in  100  c.c.  slightly 
acidified  with  nitric  acid  and  containing  a  few  per-cents  of  molybdic  acid 
solution. 

f  Zeitschr.  f.  anal.  Chem.  3,  446,  and  6,  403. 

\  Silicic  acid  may  also  be  thrown  down,  in  form  of  a  yellow  precipitate,  by 
acid  solution  of  ammonium  molybdate,  especially  in  presence  of  much  ammo- 
nium chloride  (W.  KNOP,  Chem.  Centralb.  1857,  691).  Mr.  GRUNDMANN,  who 
repeated  KNOP'S  experiments  in  my  laboratory,  obtained  the  same  results.  The 
precipitate  dissolves  in  ammonia.  If  the  solution,  after  addition  of  some  ammo- 
nium chloride,  is  allowed  to  stand  for  some  time,  the  silicic  acid  separates,  and 
the  phosphoric  acid  may  then  be  precipitated  from  the  filtrate  with  magnesia- 
mixture;  it  is,  however,  always  the  safer  way  to  remove  silicic  acid  first. 


§  134.]  PHOSPHORIC    ACID.  377 

y.  Indirect  determination,  with  previous  precipitation  as  mer- 
curous phosphate,  after  H.  HOSE.* 

Applicable  for  the  separation  of  phosphoric  acid  (also  of  pyro^ 
and  metaphosphoric  acid)  from  all  basic  radicals,  except  aluminium. 
Comp.  §  135,  L 

Dissolve  the  phosphate  in  neither  too  large  nor  too  small  a 
quantity  of  nitric  'acid,  in  a  porcelain  dish,  add  pure  metallic  mer- 
cury in  sufficient  quantity  to  leave  a  portion,  even  though  only  a 
small  one,  undissolved  by  the  free  acid.  Evaporate  on  the  water- 
bath  to  dryness.  If  the  warm  mass  still  evolves  an  odor  of  nitric 
acid,  moisten  it  with  water,  and  heat  again  on  the  water-bath,  until 
it  smells  no  longer  of  nitric  acid.  Add  now  hot  water,  pass  through 
a  small  filter,  and  wash  until  the  washings  leave  no  longer  a  fixed 
residue  upon  platinum.  Dry  the  filter,  which,  besides  mercurous- 
phosphate,  contains  also  basic  mercurous  nitrate  and  free  mercury,, 
mix  its  contents,  in  a  platinum  crucible,  with  mixed  sodium  and 
potassium  carbonates  in  excess,  roll  the  filter  into  the  shape  of  a 
ball,  place  it  in  a  hollow  made  in  the  mixture,  and  cover  the  whole 
with  a  layer  of  the  mixed  carbonates.  Expose  the  crucible,  under 
a  chimney  with  good  draught,  for  about  half  an  hour  to  a  moderate 
heat,  so  that  it  does  not  get  red-hot.  At  this  temperature,  the 
mercurous  nitrate  and  the  metallic  mercury  volatilize.  Heat  now 
over  the  lamp  to  bright  redness,  and  treat  the  residue  with  hot' 
water,  which  will  dissolve  it  completely,  if  no  ferric  oxide  be 
present,  and  if  no  oxide  of  platinum  has  been  formed.  The  latter 
may  occur  on  account  of  too  rapid  heating,  which  might  produce 
sodium  nitrate,  which  would  act  upon  the  platinum.  Supersatu- 
rate the  clear  (if  necessary,  filtered)  solution  with  hydrochloric 
acid,  add  ammonia  and  magnesia-mixture,  and  proceed  as  in  a. 

d.  Indirect  determination,  with  previous  precipitation  as  stan- 
nic phosphate. 

After  GiRAKD.f  Dissolve  the  substance  in  highly  concentrated 
nitric  acid,  remove  all  chlorine  either  by  precipitation  with  silver 
nitrate  or  by  repeated  evaporation  with  nitric  acid,  add  8  times  as- 
much  tinfoil  as  there  is  phosphoric  acid  present,  and  warm  the 
mixture  5  or  6  hours,  until  the  precipitate  has  completely  subsided, 
leaving  the  supernatant  fluid  clear.  Wash  with  hot  water  by 
decantation  and  finally  by  filtration.  The  precipitate  consists  of 

*  Pogg.  Annal.  76,  218. 

f  Compt.  rend.  54,  468;  Zeitschrift  f  analyt,  Chem.  I,  366. 


378  DETERMINATION.  [§  134. 

metastannic  acid  and  stannic  phosphate,  together  with  a  little  ferric 
and  aluminium  phosphate.  Heat  it  either  at  first  with  a  small 
quantity  of  aqua  regia,  and  then  with  ammonia  and  ammonium 
sulphide,  or  immediately  with  ammonium  sulphide  in  excess.  The 
last  process  is  recommended  by  O.  BABER,*  on  the  ground  that  the 
former  leaves  a  little  phosphoric  acid  in  the  precipitate.  The 
whole  is  digested  about  two  hours,  and  then  filtered ;  the  precipi- 
tate, consisting  of  ferrous  sulphide  and  aluminium  hydroxide,  is 
washed  with  warm  ammonium  sulphide,  then  with  water  contain- 
ing a  little  ammonium  sulphide,  dissolved  in  nitric  acid,  and  the 
solution  thus  formed  mixed  with  the  filtrate  from  the  tin  precipi- 
tate which  contains  the  principal  quantity  of  the  basic  metals. 
From  the  ammonium  -sulphide  filtrate,  which  contains  stannic  sul- 
phide and  ammonium  phosphate,  the  phosphoric  acid  is  at  once 
precipitated  by  magnesia-mixture.  I  may  add  that  GIRARD  con- 
siders 4  to  5  parts  tin  sufficient  for  1  part  P2O5.  The  results 
afforded  by  his  test-analyses  are  unexceptionable.  According  to 
jANovsKY,f  at  least  six  parts  of  tin  must  be  used.  The  tin  should 
be  free  from  arsenic. 

c.  Determination  as  TJrcmyl  Pyrophosphate. 

After  LECONTE,  A.  ARENDT,  and  W.  KNOP.^:  (Very  suitable 
in  presence  of  alkali  and  alkali-earth  metals,  but  not  in  presence  of 
any  notable  amount  of  aluminium  ;  in  presence  of  ferric  iron,  the 
method  can  be  applied  only  with  certain  modifications. )§  Where 
it  is  possible,  prepare  an  acetic  acid  solution  of  the  compound.  If 
jou  have  a  nitric  or  hydrochloric  acid  solution,  remove  the  greater 
portion  of  the  free  acid  by  evaporation,  add  ammonia  until  red 
litmus  paper  dipped  into  it  turns  very  distinctly  blue,  and  then 
redissolve  the  precipitate  formed  in  acetic  acid.  If  mineral  acids 
were  present,  add  also  some  ammonium  acetate ;  this  addition  is 
beneficial  under  any  circumstances.  Mix  the  fluid  now  with  solu- 
tion of  uranyl  acetate,  and  heat  the  mixture  to  boiling,  which  will 
cause  the  phosphoric  acid  to  separate,  in  form  of  pale  greenish- 
yellow  ammonium  uranyl  phosphate. 

*  Zeitschr.  f.  die  gesammten  Naturwissensch.  1864,  293. 

f  Zeitschr.  f.  anal.  Chem.  11,  157. 

\  LECONTE  was  the  first  to  recommend  the  method  of  precipitating  phospho- 
ric acid  from  acetic  acid  solutions  by  means  of  a  salt  of  uranium  (Jahresb.  von 
LIEBIG  und  KOPP,  fiir  1853,  642);  A.  ARENDT  and  W.  KNOP  have  subsequently 
subjected  k  to  a  careful  and  searching  examination  (Chem.  Centralbl.  1856,  769, 
803;  and  1857,  177).  §  Chem.  Centralbl.  1857,  182. 


§  134.]  PHOSPHORIC   ACID.  379 

Wash  the  precipitate,  first  by  decantation,  boiling  up  each  time, 
then  by  filtration ;  the  operation  may  be  materially  facilitated  by 
adding  a  few  per-cents  of  ammonium  nitrate  to  the  water.  Dry 
the  precipitate,  and  ignite  as  directed  §  53.  It  is  advisable  to 
evaporate  small  quantities  of  nitric  acid  on  the  ignited  precipitate 
repeatedly,  and  to  reignite.  The  residue  must  have  the  color  of 
the  yolk  of  an  egg.  For  the  properties  of  the  precipitate  and  resi- 
due, see  §  93,  4,  e.  Should  it  be  necessary  to  dissolve  the  ignited 
residue  again,  for  the  purpose  of  reprecipitating  it,  this  can  be  done 
only  after  fusing  it  with  a  large  excess  of  mixed  sodium  and  potas- 
sium carbonates,  and  thereby  converting  the  pyrophosphoric  into 
orthophosphoric  acid.  Results  accurate  ;  compare  the  test-analyses 
given  by  the  authors,  Expt.  No.  90,  and  KISSEL'S  experiments.* 

d»  Deter  minati<m  as  Bazic  Ferric  Phosphate. 

a.  Mix  the  acid  fluid  containing  the  phosphoric  acid  with  an 
excess  of  solution  of  ferric  chloride  of  known  strength,  add,  if 
necessary,  sufficient  ammonia  to  neutralize  the  greater  portion  of 
the  free  acid,  mix  with  ammonium  acetate  in  not  too  large  excess, 
and  boil.  If  the  quantity  of  solution  of  ferric  chloride  added  was 
sufficient,  the  precipitate  must  be  brownish-red.  This  precipitate 
consists  of  basic  ferric  phosphate  and  basic  ferric  acetate,  and  con- 
tains the  whole  of  the  phosphoric  acid  and  of  the  ferric  iron.  Fil- 
ter off  boiling,  wash  with  boiling  water  mixed  with  some  ammo- 
nium acetate,  dry  carefully.  [Detach  the  greater  part  of  the 
precipitate  from  the  filter,  incinerate  the  filter,  transfer '  to  the 
crucible  the  main  part  of  the  precipitate,  moisten  with  strong 
nitric  acid,  dry,  moisten  again  with  nitric  acid  and  dry  and  ignite 
— without  these  precautions  reduction  of  ferric  oxide  to  magnetic 
oxide  is  liable  to  occur.]  Deduct  from  the  weight  of  the  residue 
that  ferric  oxide  produced  from  the  solution  added  ;  the  difference 
is  the  P2  O5. 

[This  modification  of  SCHULZE'S  method  was  first  recommended 
by  A.  MULLER  ;f  it  has  been  adopted  also  by  WAY  and  OGSTON,  in 
their  analyses  of  ashes.J  MULLER'S  improvement  consists  in  the 
use  of  a  solution  of  ferric  chloride  of  known  strength,  whereby  the 
determination  of  iron  in  the  residue  is  dispensed  with.] 

ft.  J.  WEEREN'S  method,  suitable  for  the  estimation  of  the  phos- 


*  Zeitschr.  f.  anal.  Chem.  8,  167.  f  Journ.  f.  prakt.  Chem.  47,  341. 

t  Journal  of  the  Royal  Agricultural  Society,  viii.  part  i. 


380  DETERMINATION.  [§  134. 

phoric  acid  in  phosphates  of  the  alkali  and  alkali-earth  metals.* 
Mix  the  nitric  acid  solution  of  the  phosphate  under  examination, 
which  must  contain  no  other  strong  acid,  with  a  solution  of  ferric 
nitrate,  of  known  strength,  in  sufficient  proportion  to  insure  the 
formation  of  a  basic  salt  (2  or  3  parts  of  iron  should  be  present  for 
1  part  P2O6) ;  evaporate  to  dryness,  heat  the  residue  to  160°,  until 
no  more  nitric  acid  fumes  escape,  treat  with  hot  water  containing 
ammonium  nitrate  until  all  nitrates  of  the  alkali  and  alkali-earth 
metals  are  removed,  collect  the  yellow-ochreous  precipitate  on  a 
filter,  dry,  ignite  (see  §  53),  weigh,  and  deduct  from  the  weight 
the  quantity  of  iron  added  reckoned  as  ferric  oxide.  LATSCHiNowf 
recommends  heating  the  residue  to  200°,  warming  with  water  and 
a  few  drops  of  sulphuric  acid,  adding  ammonia  and  then  treating 
with  hot  solution  of  ammonium  nitrate.  He  says  that  the  phos- 
phoric acid  is  thus  rnore  completely  separated,  and  the  precipitate 
may  be  more  readily  filtered  off. 

e.  Determination  as  Normal  Magnesium  Phosphate  Mg9 
(PO.), 

(FR.  SCHULZE'S  method,  suitable  more  particularly  to  effect  the 
separation  of  phosphoric  acid  from  the  alkalies.:):) 

Mix  the  solution  of  the  alkali  phosphate,  which  contains  ammo- 
nium chloride,  with  a  weighed  excess  of  pure  magnesium  oxide, 
evaporate  to  dry  ness,  ignite  the  residue  until  the  ammonium  chlo- 
ride is  expelled,  and  separate  the  magnesium,  which  is  still  present 
in  form  of  magnesium  chloride,  by  means  of  mercuric  oxide  (§  153, 
4,  y).  Treat  the  ignited  residue  with  water,  filter  the  solution  of 
the  chlorides  of  the  alkali  metals,  wash  the  precipitate,  dry,  ignite, 
and  weigh.  The  excess  of  weight  over  that  of  the  magnesium 
oxide  used  shows  the  quantity  of  the  P2O5.  Results  satisfactory. 

f.  SCHLOSING'S  method§  does  not  appear  to  offer  any  advan- 
tages. The  phosphate  is  mixed  with  silica  and  ignited  in  carbon 
monoxide,  the  expelled  phosphorus  being  taken  up  by  copper  or  by 
silver  nitrate. 

y.  Determination  by  Volumetric  Analysis  (  With  Uranium 
Solution). 

This  method  was  recommended  originally  by  LECONTE.||      It 

*  Journ.  f.  prakt.  Chem.  67,  8.  f  Zeitschr.  1  anal.  Chem.  7,  213. 

\  Journ.  f.  prakt.  Chem.  63,  440. 
§  Zeitschr.  f.  anal.  Chem.  4,  118,  and  7,  473. 
J  Jahresber.  von  LIEBIG  u.  KOPP,  f iir  1853,  642. 


§  134.]  PHOSPHORIC    ACID.  381 

was  improved  and  described  ~  in  detail  by  NEUBAUER,*  and  was 
afterwards  recommended  by  PINCUS,  f  and  subsequently  by 
BODEKER.J  The  principle  of  the  method  is  as  follows  :  uranyl 
acetate  precipitates  from  solutions  rendered  acid  by  acetic  acid, 
hydrogen  uranyl  phosphate,  or — in  the  presence  of  considerable 
quantities  of  ammonium  salts — ammonium  uranyl  phosphate.  The 
proportion  between  the  uranium  and  the  phosphoric  acid  is  the 
same  in  both  compounds.  Both  compounds  when  freshly  precipi- 
tated and  suspended  in  water  are  left  unchanged  by  potassium 
ferrocyanide ;  uranyl  acetate,  on  the  other  hand,  is  indicated  by 
this  reagent  with  great  delicacy  by  the  formation  of  an  insoluble 
reddish-brown  precipitate. 

According  to  NEUBAUER§  the  following  solutions  are  employed : 

a.  A  solution   of  phosphoric  add  of  known  strength.     Pre- 
pared by  dissolving  10*085  grm.  pure,  crystallized,  uneffloresced, 
powdered,  and  pressed  hydrogen  sodium  phosphate  in  water  to  1 
litre.     50  c.c.  contain  *1  grm.  P2O5.     It  is  well  to  control  this  solu- 
tion by  evaporating  50  c.c.  in  a  weighed  platinum  dish  to  dryness, 
igniting  strongly,  and  weighing.     The  weight  should  be  *  1 874  grm. 

b.  An  acid  solution  of  sodium  acetate.     Prepared  by  dissolv- 
ing 100  grm.  sodium  acetate  in  900  water,  and  adding  acetic  acid 
of  1*04  sp.  gr.  to  1  litre. 

c.  A  solution  of  uranyl  acetate  (§  63,  3).     This  is  standardized 
by  means  of  the  hydrogen  sodium  phosphate  solution.     1  c.c.  indi- 
cates *005  grm.  P2O5.    The  solution  is  made  at  first  a  little  stronger 
than  necessary,  so  that  it  may  contain  in  the  litre,  say,  32*5  grm. 
UO2(C2H3O2)a  +  2H2O   or  34   grm.  UO9(C2H3O2)2  +  3H2O  (corre- 
sponding to  22   grm.   UO2O),  its  value  is  determined,  and  it  is 
diluted  accordingly.     To  determine  its  value  proceed  as  follows  : 
Transfer  50  c.c.  of  the  a  solution  to  a  beaker,  add  5  c.c.  of  the  b 
solution,  and  heat  in  a  water-bath  to  90 — 100°.     Now  run  in  ura- 
nium solution,  at  first  a  large  quantity,  at  last  in  ^  c.c.,  testing  after 
each  addition  whether  the  precipitation  is  finished  or  not.     For 
this  purpose  spread  out  one  or  two  drops  of  the  mixture  on  a  white 
porcelain  surface  and  introduce  into  the  middle,  by  means  of  a  thin 
glass  rod,  a  small  drop  of  freshly  prepared  potassium  ferrocyanide 
solution  or  a  little  of  the  powdered  salt.     As  soon  as  a  trace  of 

*  Archiv.  filr  wissenschaftliche  Heilkunde,  4,  228. 

t  Journ.  f.  prakt.  Chem.  76, 104.        \  Anal.  d.  Chem.  u.  Pharm.  117,  195. 

§  His  Anleitung  zur  Harnanalyse,  6  Aufl.  171. 


382  DETERMINATION.  [§  134. 

excess  of  uranyl  acetate  is  present,  a  reddish-brown  spot  forms  in 
the  drop,  which,  surrounded  as  it  is  by  the  colorless  or  almost 
colorless  fluid,  may  be  very  distinctly  perceived.  When  the  final 
reaction  has  just  appeared,  heat  a  few  minutes  in  the  water-bath 
and  repeat  the  testing  on  the  porcelain.  If  now  the  reaction  is 
still  plain  the  experiment  is  concluded.  If  the  uranium  solution 
had  been  exactly  of  the  required  strength,  20  c.c.  would  have  been 
used ;  but  it  is  actually  too  concentrated,  Ii3nce  less  than  20  c.c. 
must  have  been  used.  Suppose  it  was  18  c.c.,  then  the  solution 
will  be  right,  if  for  every  18  c.c.  we  add  2  c.c.  of  water.  If  in  this 
first  experiment  we  find  that  the  solution  is  much  too  strong,  the 
solution  is  diluted  with  somewhat  less  water  than  is  properly  speak- 
ing required,  another  experiment  is  made,  and  it  is  then  diluted 
exactly. 

The  actual  analysis  must  be  made  under  as  nearly  as  possible 
similar  circumstances  to  those  under  which  the  standardizing  of  the 
uranium  solution  was  performed,  especially  as  regards  the  sodium 
acetate.  This  salt  retards  the  precipitation  of  uranium  by  potas- 
sium ferrocyanide,  hence  the  test-drop  on  the  porcelain  plate 
becomes  darker  and  darker.  The  analyst  should  accustom  himself 
to  observing  the  first  appearance  of  the  slightest  brownish  colora- 
tion in  the  middle  of  the  drop,  and  should  take  this  as  the  end- 
reaction.  It  need  hardly  be  added  that  the  same  person  must 
make  the  analysis  who  has  standardized  the  solution  (NEUBAUER). 

The  method  is  applicable  to  free  phosphoric  acid,  alkali  phos- 
phates, and  magnesium  phosphate,  also  in  the  presence  of  small 
quantities  of  the  phosphates  of  other  alkali-earth  metals,  but  can- 
not be  employed  in  presence  of  ferric  and  aluminium  salts.  Dis- 
solve the  substance  in  water  or  the  least  possible  quantity  of  acetic 
acid,  add  5  c.c.  of  the  b  solution,  dilute  to  50  c.c.,  and  proceed  with 
the  addition  of  uranium  as  above.  The  results  are  very  satisfac- 
tory. Compare  KISSEL'S  experiments.*  If  the  above  process  is 
followed  in  the  presence  of  much  calcium,  for  instance  with  a  solu- 
tion of  calcium  phosphate  in  dilute  acetic  acid,  the  results  are 
almost  always  too  low,  as  little  calcium  phosphate  is  precipitated 
along  with  uranyl  phosphate.  [The  best  means  of  obviating  that 
error  is,  according  to  ABESSER,  JANI,  and  MARCKER,-)-  to  standardize 
the  uranium  solution  under  the  same  conditions  as  near  as  possible 


*  Zeitschr.  f.  anal.  Chem.  8,  167.  f  Ib.  12, 


§  135.]  PHOSPHORIC   ACID.  383 

as  exist  when  the  solution  is  used  for  the  actual  determination  of 
phosphoric  acid.  It  must  therefore  be  standardized  with  calcium 
phosphate.  Prepare  a  solution  of  suitable  strength  by  dissolving 
pure  Ca3(PO4)a  in  the  smallest  possible  quantity  of  nitric  acid  and 
diluting  to  the  desired  volume.  Determine  accurately  the  amount 
of  Ca3(PO)4  in  this  solution  by  evaporating  to  dryness  in  a  plati- 
num vessel  50  c.c.,  moistening  the  residue  with  ammonia  and  ignit- 
ing. The  residual  somewhat  hygroscopic  calcium  phosphate  is 
quickly  weighed  in  the  covered  platinum  vessel]. 

II.  SEPARATION  OF  PHOSPHORIC  ACID  FROM  THE  BASIC  RADICALS. 

§  135. 

a.  From  the  Alkalies  (see  also  d,  &,  and  Z). 

a.  Add  ammonium  chloride,  or  hydrochloric  acid,  then  lead 
acetate,  exactly,  till  no  more  precipitate  is  produced,  and  lastly 
some  pure  lead  carbonate  (prepared  by  precipitating  lead  acetate 
with  ammonium  carbonate,  BASER*),  allow  to  digest  for  some  time, 
niter  off  the  precipitate  consisting  of  lead  phosphate,  chloride,  and 
carbonate,  wash,  precipitate  from  the  filtrate  the  slight  excess  of 
lead  by  hydrogen  sulphide,  filter  and  evaporate  with  hydrochloric 
acid  (in  the  case  of  lithium,  sulphuric  acid).     If  the  phosphoric 
acid  is  to  be  estimated  in  the  same  portion,  proceed  with  the  first 
precipitate  (after  washing  to  remove  the  larger  quantity  of  chlo- 
ride), according  to  b. 

/3.  (Only  applicable  in  the  case  of  fixed  alkalies.)  Separate  the 
phosphoric  acid  as  ferric  phosphate,  according  to  one  of  the  meth- 
ods given  §  134,  d.  Or  if  you  do  not  wish  to  determine  the  phos- 
phoric acid  it  is  very  convenient  to  acidify  with  hydrochloric  acid, 
add  ferric  chloride,  dilute  rather  considerably,  add  ammonia  till  the 
fluid  is  neutral,  and  boil ;  all  the  phosphoric  acid  will  then  separate 
with  ferric  oxychloride  as  ferric  phosphate.  The  separation  of 
phosphoric  acid  may  also  be  effected  as  magnesium  phosphate 
(§  134,  e).  The  alkalies  are  contained  in  the  filtrate  as  nitrates  or 
chlorides. 

b.  From  Barium,  Strontium,  Calcium,  and  Lead. 

The  compound  under  examination  is  dissolved  in  hydrochloric 
or  nitric  acid,  and  the  solution  precipitated  with  sulphuric  acid  in 

*  Zeitschr.  f.  die  ges.  Naturwiss.  1864,  298;  Zeitschr.  f.  anal.  Chem.  4,  120 


584  DETERMINATION.  [§  135. 

slight  excess.  In  the  separation  of  phosphoric  acid  from  strontium, 
calcium,  and  lead,  alcohol  is  added  with  the  sulphuric  acid.  The 
phosphoric  acid  in  the  filtrate  is  determined  according  to  §  134,  &, 
a-,  after  removal  of  the  alcohol  by  evaporation.  The  determination 
of  the  phosphoric  acid  is  effected  most  accurately  by  saturating  the 
fluid  with  sodium  carbonate,  evaporating  to  dry  ness,  and  fusing  the 
residue  with  sodium  and  potassium  carbonates.  The  fused  mass  is 
then  dissolved  in  water,  and  the  further  process  conducted  as  in 
§  134,  b,  a. 

c.  From  Magnesium  (see  also  d,  A,  &,  I). 

Add  ferric  chloride  in  sufficient  excess,  dilute,  add  excess  of 
"barium  carbonate,  allow  to  remain  for  several  hours  with  frequent 
stirring,  filter  and  separate  magnesium  and  barium  in  the  filtrate 
-after  §  154. 

d.  From  the  whole  of  the  Alkali-earth  Metals  and  fixed  Alka- 
ities  (comp.  A,  &,  I). 

a.  Dissolve  in  the  least  possible  quantity  of  nitric  acid,  add  a 
little  ammonium  chloride,  precipitate  exactly  with  lead  acetate,  add 
a  little  lead  carbonate  (precipitated),  digest,  filter,  precipitate  the 
^excess  of  lead  rapidly  from  the  filtrate  by  hydrogen  sulphide,  filter 
and  determine  the  basic  metals  in  the  filtrate.  Results  good. 

ft.  Dissolve  in  water,  and — in  case  of  phosphates  of  the  alkali- 
earth  metals — the  least  possible  nitric  acid,  add  neutral  silver  nitrate 
and  then  silver  carbonate,  till  the  fluid  reacts  neutral.  All  phos- 
phoric acid  now  separates  as  Ag3PO4.  Warming  is  unnecessary. 
Filter,  wash  the  precipitate,  dissolve  it  in  dilute  nitric  acid,  precipi- 
tate the  silver  with  hydrochloric  acid,  and  determine  the  phosphoric 
acid  in  the  filtrate  according  to  §  134,  &,  OL.  The  filtrate  from  the 
.silver  phosphate  is  freed  from  silver  by  hydrochloric  acid,  and  the 
basic  metals  are  then  determined  according  to  the  methods  already 
given  (G.  CHANCEL*).  A  good  and  convenient  method  unless  the 
proportion  of  alkali  is  very  large.  (If  the  substance  contains  alu- 
minium or  ferric  iron,  they  are  completely  precipitated  by  the 
silver  carbonate,  and  are  found  with  the  silver  phosphate.) 

y.  Separate  the  phosphoric  acid  as  uranyl  phosphate  (§  134,  c), 
and  the  excess  of  uranium  from  the  alkali-earth  metals,  &c..  in  the 
filtrate,  according  to  §§  160  and  161,  Supplement.  Results  good. 

#.  Separate  the  phosphoric  acid  according  to  §134,  d,  OL  or  ft. 

*  Cotnpt.  rend.  49,  997 


§  135.]  PHOSPHORIC    ACID.  385 

The  alkali-earth  metals  are  obtained  in  solution  in  the  first  case,  as 
chlorides,  together  with  alkali  acetate  and  chloride ;  in  the  second 
case  as  nitrates.  .Results  good. 

e.  From  Aluminium. 

The  best  method  of  separating  phosphoric  acid  from  aluminium 
is  that  depending  on  precipitation  by  ammonium  molybdate  (I). 
The  separation  of  the  acid  as  stannic  phosphate  (A,  a)  is  also  satis- 
factory. 

Of  several  other  methods  which  have  been  used,  the  following 
(by  WACKEXRODER  and  FRESENIUS)  is  one  of  easiest  to  carry  out : 
Precipitate  the  not  too  acid  solution  with  ammonia,  taking  care 
not  to  use  a  great  excess  of  that  reagent,  and  add  barium  chloride 
as  long  as  a  precipitate  continues  to  form.  Digest  for  some  time, 
and  then  filter.  The  precipitate  contains  the  whole  of  the  alumin- 
ium and  the  whole  of  the  phosphoric  acid;  the  latter  combined 
partly  with  aluminium,  partly  with  barium.  Filter  it  off,  wash  it 
a  little,  and  dissolve  in  the  least  possible  quantity  of  hydrochloric 
acid.  Warm,  saturate  the  solution  with  barium  carbonate,  add 
pure  solution  of  potassa  in  excess,  apply  heat,  precipitate  the 
barium  which  the  solution  may  contain  with  sodium  carbonate, 
and  filter.  You  have  now  the  whole  of  the  aluminium  in  the 
solution,  the  whole  of  the  phosphoric  acid  in  the  precipitate. 
Acidify  the  solution  with  hydrochloric  acid,  boil  with  some  potas- 
sium chlorate,  and  precipitate  as  directed  §  105.  Dissolve  the  pre- 
cipitate in  hydrochloric  acid,  precipitate  the  barium  with  dilute 
sulphuric  acid,  filter,  and  determine  the  phosphoric  acid  in  the 
filtrate  by  precipitation  with  solution  of  magnesium  in  the  manner 
described  in  §  13-i,  &,  a.  (HERMANN  has  applied  a  perfectly  simi- 
lar method  in  his  analysis  of  [impure]  gibbsite.) 

f.  From  Chromium  (see  also  A,  &,  I). 

Fuse  with  sodium  carbonate  and  nitrate,  and  separate  the 
chromic  acid  and  phosphoric  acid  in  the  manner  described  §  166. 

g.  From  the  Metals  of  the  Fou-rth.  Group  (see  also  //,  #.  7\ 

a.  The  method  so  often  used  of  fusing  with  sodium  carbonate 
does  not  give  accurate  results  on  account  of  the  constant  presence 
of  some  phosphoric  acid  in  the  washed  residue.  Compare  W. 
SCHWEIKERT*  and  G.  SCHWEITZER.+  The  former  has  studied  the 


*Annal.  d.  Chem.  u.  Pharm.  145,  57;  Zeitschr.  f.  anal.  Chem.  7,  246. 
f  Zeitschr.  f  anal.  Chem.  9,  84. 


386  DETERMINATION.  [§  135. 

separation  of  zinc  from  phosphoric  acid  by  this  method,  the  latter 
the  separation  of  iron. 

/?.  Dissolve  in  hydrochloric  acid,  add  tartaric  acid,  ammonium 
chloride  and  ammonia,  and  finally,  in  a  flask  which  is  to  be  closed 
afterwards,  ammonium  sulphide,  put  the  flask  in  a  moderately 
warm  place,  allowing  the  mixture  to  deposit  until  the  fluid  appears 
of  a  yellow  color,  without  the  least  tint  of  green  ;  filter,  and  deter- 
mine the  metals  as  directed  in  §§  108  to  114.  The  phosphoric 
acid  is  found  from  the  loss  or  determined  according  to  §  134,  J,  a. 
The  magnesia-mixture  may  immediately  be  added  to  the  filtrate, 
which  contains  ammonium  sulphide.  The  washed  precipitate  is 
redissolved  in  just  sufficient  hydrochloric  acid,  and  the  solution 
reprecipitated  by  ammonia  with  addition  of  magnesia-mixture. 
This  method  is  not  well  adapted  for  nickelous  phosphate. 

h.  From  Metals  of  the  Second,  Third,  and  Fourth  Groups. 

OL.  More  especially  from  the  second  group,  aluminium,  manga- 
nese, nickel,  cobalt,  zinc  ;  and  also  from  ferric  iron,  if  the  quantity 
of  the  latter  is  not  too  considerable. 

The  phosphoric  acid  is  precipitated  as  stannic  phosphate, 
according  to  §  134,  b,  <?.  The  filtrate  contains  the  bases  free 
from  any  foreign  body  requiring  removal,  which,  of  course,  greatly 
facilitates  their  estimation.* 

i.  From  the  Metals  of  the  Fifth  and  Sixth  Groups. 

Dissolve  in  hydrochloric  or  nitric  acid,  precipitate  with  hydro- 
gen sulphide,  filter,  determine  the  bases  by  the  methods  given  in 
§§  115  to  127,  and  the  phosphoric  acid  in  the  filtrate  by  the  method 
described  §  134,  J,  a.  From  silver  the  phosphoric  acid  is  sepa- 
rated in  a  more  simple  way  still,  by  adding  hydrochloric  acid  to 
the  nitric  acid  solution  ;  from  lead  it  is  separated  most  readily  by 
the  method  described  in  b. 

Jc.  From  all  Basic  Metals,  except  Mercury  (H.  ROSE). 

The  phosphoric  acid  is  separated  as  mercurous  phosphate  by 
ROSE'S  method  (§  134,  I,  y}. 

a.  If  the.  substance  is  free  from  iron  and  aluminium,  the 
filtrate  from  the  mercurous  phosphate  contains  all  the  metals  as 
nitrates,  together  with  much  mercurous  nitrate,  and  occasionally 

*  If  the  nitric  acid  is  not  concentrated,  a  little  nitrate  of  protoxide  of  tin  is 
formed,  which  dissolves  and  must  afterwards  be  precipitated  from  the  acid  fluid 
by  sulphuretted  hydrogen.  BABEK,  Zeitschr.  f.  d.  ges.  Naturwiss.  1864,  324. 


g  135.]  PHOSPHORIC    ACID.  387 

also  some  mercuric  salt.  The  former  is  removed  by  the  addition 
of  hydrochloric  acid.  The  precipitated  mercurous  chloride  is  free 
from  other  metals :  if  large  in  quantity,  it  should  be  separated  by 
filtering ;  if  slight,  filtering  may  be  omitted.  Add  next  ammonia 
to  slight  alkaline  .reaction  (with  previous  addition  of  ammonium 
chloride  if  magnesium  is  present).  Filter  rapidly  from  the  mer- 
cury compound  which  will  be  precipitated  so  as  to  avoid  forma- 
tion of  calcium  carbonate  by  contact  with  air.  The  filtrate  contains 
the  basic  radicals  from  which  phosphoric  acid  has  been  separated. 
The  mercury  compound  which  has  been  separated  by  ammonia  is 
dried  and  ignited  (under  a  chimney  with  good  draught).  Should 
a  residue  remain,  this  must  be  examined.  If  it  consists  of  phos- 
phates of  the  alkali-earth  metals,  the  treatment  with  mercury  and 
nitric  acid  must  be  repeated;  if,  on  the  contrary,  it  consists  of 
magnesium  oxide  or  of  carbonates  of  the  alkali-earth  metals,  it  is 
dissolved  in  hydrochloric  acid,  and  the  solution  added  to  the  fluid 
containing  the  chief  portion  of  the  basic  metals,  which  may  then 
be  separated  and  determined  in  the  usual  manner.  The  following 
method  is  often  advantageously  resorted  to  instead  of  the  one 
described :  The  filtrate  from  the  mercurous  phosphate  is  evaporated 
to  dryness,  in  a  platinum  dish,  and  the  residue  ignited,  in  a  plati- 
num crucible,  under  a  chimney  with  good  draught.  If  alkali 
nitrates  are  present,  some  ammonium  carbonate  must  be  added 
from  time  to  time  during  the  process  of  ignition,  to  guard  against 
injury  to  the  crucible  from  the  formation  of  caustic  alkali.  The 
ignited  residue  is  treated,  according  to  circumstances,  first  with- 
water  and  then  with  nitric  acid,  or  at  once  with  nitric  acid. 

ft.  If  the  substance  contains  iron  but  not  aluminium,  the 
greater  part  of  the  iron  is  left  undissolved  with  the  mercurous 
phosphate.  The  dissolved  part  is  separatd  from  the  other  bases  by 
the  methods  given  in  Section  Y. ;  the  iron  in  the  undissolved  part 
is  obtained,  after  ignition  of  the  residue  with  sodium  carbonate 
and  treating  the  ignited  mass  with  water,  as  ferric  oxide  contain- 
ing alkali  (and  generally  also  some  phosphoric  acid).  This  is  dis- 
solved in  hydrochloric  acid,  and  precipitated  with  ammonia. 

y.  If  the  substance  contains  aluminium,  the  process  just  given 
cannot  be  used,  as  aluminium  phosphate  is  not  decomposed  by 
fusion  with  alkali  carbonates,  while  aluminium  nitrate,  like  ferric 
nitrate,  is  decomposed  by  simple  evaporation.  In  this  case  proceed 
as  follows :  Dissolve  the  substance  in  the  least  quantity  of  nitric 


388  DETERMINATION.  [§  135. 

acid,  precipitate  hot  with  mercurous  nitrate,  add  a  little  mercuric 
nitrate,  and  then  pure  potash  or  soda,  till  a  permanent  red  precipi- 
tate appears.  The  precipitate  contains  no  aluminium,  it  is  to  be 
treated  according  to  a  or  ft  (H .  ROSE,  E.  E.  MUNKOE*). 

1.  From  all  Bases  witJiout  exception. 

Apply  SONNENSCHEIN'S  method  (§  134,  &,  /?),  and  in  the  filtrate 
from  the  ammonium  phospho-molybdate  separate  the  bases  from 
the  molybdic  acid.  As  molybdic  acid  comports  itself  with  hydro- 
gen sulphide  and  ammonium  sulphide  like  a  metal  of  the  sixth 
group,  it  is  best  to  precipitate  metals  of  the  sixth  and  also  of  the 
fifth  group  from  acid  solution  with  hydrogen  sulphide,  before  pro- 
ceeding to  precipitate  the  phosphoric  acid  with  molybdic  acid ;  the 
latter  will  then  have  to  be  separated  only  from  the  metals  of  the 
tirst  four  groups.  This  is  done  in  the  following  manner :  Mix  the 
acid  fluid,  in  a  flask,  with  ammonia  till  it  acquires  an  alkaline 
reaction,  add  ammonium  sulphide  in  sufficient  excess,  close  the 
mouth  of  the  flask,  and  digest  the  mixture.  As  soon  as  the  solution 
appears  of  a  reddish-yellow  color,  without  the  least  tint  of  green, 
filter  off  the  fluid,  which  contains  molybdenum  and  ammonium 
sulphide,  wash  the  residue  with  water  mixed  with  some  ammonium 
sulphide,  and  separate  the  remaining  metallic  sulphides  and  hydrox- 
ides of  the  fourth  and  third  groups  by  the  methods  which  will  be 
found  in  Section  Y.  Mix  the  filtrate  cautiously  with  hydrochloric 
acid  in  moderate  excess,  remove  the  molybdenum  sulphide  accord- 
ing to  §  128,  d,  and  determine  the  metals  of  the  first  and  second 
groups  in  the  filtrate. 

This  method  of  separating  the  phosphoric  acid  from  basic  radi- 
cals is  highly  to  be  recommended ;  especially  in  cases  where  a 
small  quantity  of  phosphoric  acid  has  to  be  determined  in  presence 
of  a  very  large  quantity  of  ferric  and  aluminium  salts,  as,  for  exam- 
ple, in  iron  ores,  soils,  &c.  As  arsenic  acid  and  silicic  acid  give, 
with  molybdic  acid  and  ammonia,  similar  yellow  precipitates,  it  is 
necessary,  if  these  acids  are  present,  to  remove  them  first. 

As  the  separation  of  the  basic  metals  from  the  large  excess  of 
molybdic  acid  used  is  somewhat  tedious,  the  best  way  is  to  arrange 
matters  so  that  this  process  may  be  altogether  dispensed  with. 
Supposing,  for  instance,  you  have  a  fluid  containing  ferric  iron, 
aluminium,  and  phosphoric  acid,  estimate,  in  one  portion,  by  cau- 


Amer.  Journ.  of  Sci.  and  Arts,  May,  1871;  Zeitschr.  f.  anal.  Chem.  10,  467. 


£  136.]  BOKIC    ACID    AND    BORIC    AMIYDRIDK.  389 

tious  precipitation  with  ammonia,  the  total  amount  of  the  three 
bodies ;  in  another  portion  the  phosphoric  acid,  by  means  of  molyb- 
dic  acid;  and  in  a  third,  the  iron,  in  the  volumetric  way.  The 
aluminium  can  then  be  calculated  by  difference. 

§136. 
BOEIC  ACID  (H3BO3)  AND  BORIC  ANHYDRIDE  (B,O3). 

I.  Determination. 

Boric  acid  is  estimated  either  indirectly  or  in  the  form  ofpotas- 
sium  borofluoride. 

1.  The  determination  of  the  boric  acid  in  an  aqueous  or  alco- 
holic solution  cannot  be  effected  by  simply  evaporating  the  fluid 
and  weighing  the  residue,  as  a  notable  portion  of  the  acid  volatil- 
izes and  is  carried  off  with  the  aqueous  or  alcoholic  vapor.  *  This 
is  the  case  also  when  the  solution  is  evaporated  with  lead  oxide  in 
excess. 

a.  Mix  the  solution  of  the  boric  acid  with  a  weighed  quantity 
of  perfectly  anhydrous  pure  sodium  carbonate,  in  amount  about  \% 
times  the  supposed  quantity  of  B2O3  present.     Evaporate  the  mix- 
ture to  dryness,  heat  the  residue  to  fusion,  and  weigh.     The  residue 
contains  a  known  amount  of  Na2O,  and  unknown  quantities  of  COa 
and  B2O3  combined  as  sodium  borate  and  carbonate.     Determine 
the  CO,  by  one  of  the  methods  given  in  §  139,  and  find  the  B,O, 
from  the  difference  (H.  ROSE). 

b.  In  the  method  a,  if  between  ]  and  2  mol.  sodium  carbonate 
(  XaaCO8)  are  used  to  1  mol.  B2O3 — and  this  can  easily  be  done  if 
one  knows  approximately  the  amount  of  the  latter  present — all  the 
carbonic  acid  is  expelled  by  the  boracic  acid.    Hence  we  have  only 
to  deduct  the  Na8O  from  the  residue  to  find  the  B,OS.    As  the 
tumultuous  escape  of  carbonic  acid  may  lead  to  loss,  it  is  well,  after 
having  thoroughly  dried  the  residual  saline  mass,  to  project  it  in 
small  portions  cautiously  into  the  red-hot  crucible.     Results  good 
(F.  G.  SCHAFFGOTSCH).* 

c.  When  the  amount  of  acid  is  quite  unknown,  and  an  estima- 
tion of  carbonic  acid  in  the  residue  is  objected  to,  you  may  proceed 
thus :  Evaporate  the  solution  of  the  acid  with  addition  of  a  weighed 
quantity  of  anhydrous  neutral  borax  (sodium  metaborate  NaBO2) 

*  Pogg.  Ann.  107,  427. 


390  DETERMINATION.  [§  136. 

free  from  carbonic  acid  to  dryness,  and  heat  the  residue  to  redness 
with  great  caution  (on  account  of  the  intumescence)  till  the  weight 
is  constant.  The  amount  of  neutral  borax  must  be  so  adjusted 
that  it  may  not  be  entirely  converted  into  common  borax  (2NaBOa 
BaO3)  (H.  ROSE). 

d.  If  a  solution  contains,  besides  boric  acid,  only  alkalies  or 
magnesium,  the  acid  may  be  determined,  according  to  C.  MARIG- 
JSTAC,*  in  the  following  manner:  Neutralize  the  solution  with 
hydrochloric  acid,  add  double  magnesium  and  ammonium  chloride 
in  sufficient  quantity  to  give  at  least  2  parts  of  MgO  to  1  part  of 
B2O3,  then  add  ammonia  and  evaporate  to  dryness.  If  a  precipi- 
tate is  formed  on  adding  the  ammonia  which  does  not  redissolve 
readily  on  warming,  add  more  ammonium  chloride.  The  evapora- 
tion is  conducted,  at  least  towards  the  end,  in  a  platinum  dish,  a 
few  drops  of  ammonia  being  added  from  time  to  time.  Ignite  the 
dry  mass,  treat  with  boiling  water,  collect  the  insoluble  precipitate 
(consisting  of  magnesium  borate  mixed  with  excess  of  magnesium 
oxide)  on  a  filter,  and  wash  with  boiling  water  till  the  washings 
remain  clear  with  nitrate  of  silver.  The  filtrate  and  washings  are 
mixed  with  ammonia,  evaporated  to  dryness,  ignited,  and  washed 
with  boiling  water  as  before. 

The  two  insoluble  residues  are  ignited  together  in  the  platinum 
dish  before  used,  as  strongly  as  possible,  and  for  a  sufficiently  long 
time,  in  order  to  decompose  the  slight  traces  of  magnesium  chlo- 
ride that  might  still  be  present.  After  weighing  determine  the 
magnesium  oxide,  and  find  the  boric  acid  from  the  difference. 
The  determination  of  the  magnesium  may  be  made  by  dissolving 
the  residue  in  hydrochloric  acid  and  precipitating  as  ammonium 
magnesium  phosphate,  or  more  quickly,  and  almost  as  accurately, 
by  dissolving  in  a  known  quantity  of  standard  sulphuric  acid  at  a 
boiling  temperature  and  determining  the  excess  of  acid  with  stand- 
ard soda  (comp.  Alkalimetry). 

Should  a  little  platinum  remain  behind  on  dissolving  the  resi- 
due, it  must  be  weighed  and  subtracted  from  the  weight  of  the 
whole  (unless  the  dish  was  weighed  first).  Results  satisfactory. 
MARIGNAC  obtained  in  two  experiments  '276  instead  of  '280. 

2.  If  boric  acid  is  to  be  determined  at>  potassium  borqfluoride, 
alkalies  only  (preferably  only  potash)  may  be  present.  The  process 


*  Zeitschr.  f.  anal.  Chem.  1,  405. 


§  136.]  BORIC   ACID   AND   BORIC   ANHYDRIDE.  391 

is  conducted  as  follows :  Mix  the  fluid  with  pure  solution  of  potassa, 
adding  for  each  mol.  boric  acid  supposed  to  be  present,  at  least  1 
mol.  potassa ;  add  pure  hydrofluoric  acid  (free  from  silicic  acid)  in 
excess,  and  evaporate,  in  a  platinum  dish,  on  the  water-bath,  to 
diyness.  The  fumes  from  the  evaporating  fluid  should  redden 
litmus  paper,  otherwise  there  is  a  deficiency  of  hydrofluoric  acid. 
The  residue  consists  now  of  KF,BFS  and  KF,HF.  Treat  the  dry 
saline  mass,  at  the  common  temperature,  with  a  solution  of  1  part 
of  potassium  acetate  in  4:  parts  of  water,  let  it  stand  a  few  hours, 
with  stirring,  then  decant  the  fluid  portion  on  to  a  weighed  filter, 
and  wash  the  precipitate  repeatedly  in  the  same  way,  finally  on  the 
filter,  with  solution  of  potassium  acetate,  until  the  last  rinsings  are 
no  longer  precipitated  by  calcium  chloride.  By  this  course  of  pro- 
ceeding, the  hydrogen  potassium  fluoride  is  removed,  without  a 
particle  of  the  potassium  borofluoride  being  dissolved.  To  "remove 
the  potassium  acetate,  wash  the  precipitate  now  with  alcohol  of  78 
per  cent.,  dry  at  100°,  and  weigh.  As  potassium  chloride, -nitrate, 
and  phosphate,  sodium  salts,  and  even,  though  with  some  difficulty, 
potassium  sulphate,  dissolve  in  solution  of  potassium  acetate,  the 
presence  of  these  salts  does  not  interfere  with  the  estimation  of  the 
boric  acid;  however,  sodium  salts  must  not  be  present  in  consider- 
able proportion,  as  sodium  fluoride  dissolves  with  very  great  diffi- 
culty. The  results  obtained  by  this  method  are  satisfactory.  STKO- 
MEYER'S  experiments  gave  from  97*5  to  10O7  instead  of  100. 
When  the  amount  of  alkali  salt  to  be  removed  is  very  large,  the 
saline  mass  left  on  evaporation  should  be  warmed  with  the  solution 
of  potassium  acetate,  allowed  to  stand  12  hours  in  the  cold  and 
then  filtered.  In  this  way  the  quantity  of  potassium  acetate 
required  will  be  much  reduced.  For  the  composition  and  proper- 
ties of  potassium  borofluoride,  see  §  93,  5.  As  the  salt  is  very 
likely  to  contain  potassium  silicofluoride  it  is  indispensable  to  test 
it  for  that  substance ;  this  is  done  by  placing  a  small  sample  of  it 
on  moist  blue  litmus  paper,  and  putting  another  sample  into  cold 
concentrated  sulphuric  acid.  If  the  blue  paper  turns  red,  and 
effervescence  ensues  in  the  sulphuric  acid,  the  salt  is  impure,  and 
contains  potassium  silicofluoride.  To  remove  this  impurity,  dis- 
solve the  remainder  of  the  salt,  after  weighing  it,  in  boiling  water, 
add  ammonia,  and  evaporate,  redissolve  in  boiling  water,  add 
ammonia,  &c.,  repeating  the  same  operation  at  least  six  times. 
Finally,  after  warming  once  more  with  ammonia,  filter  off  the 


392  DETERMINATION.  [§  136. 

silicic  acid,  evaporate  to  dryness,  and  treat  again  with  solution  of 
potassium  acetate  and  alcohol  (A.  STROMEYER).*  I  was  obliged  to 
modify  STROMEYER'S  method  for  effecting  the  separation  of  the 
silicic  acid,  the  results  of  my  experiments  having  convinced  me 
that  treating  the  salt  only  once  with  ammonia,  as  recommended  by 
that  chemist,  is  not  sufficient  to  effect  the  object  in  view. 

II.  Separation  of  Boric  Acid  from  the  Basic  Radicals* 

a.  from  the  Alkalies. 

Dissolve  a  weighed  quantity  of  the  borate  in  water,  add  an 
excess  of  hydrochloric  acid,  and  evaporate  the  solution  on  the 
water-bath.  Towards  the  end  of  the  operation  add  a  few  more 
drops  of  hydrochloric  acid,  and  keep  the  residue  on  the  water-bath, 
until  no  more  hydrochloric  acid  vapors  escape.  Determine  now 
the  chlorine  in  the  residue  (§  141),  calculate  from  this  the  alkali, 
and  you  will  find  the  boric  acid  from  the  difference. 

E.  SOHWEIZER,  with  whom  this  method  originated,  states  that 
it  gave  him  very  satisfactory  results  in  the  analysis  of  borax.  It 
will  answer  also  for  the  estimation  of  the  basic  metals  in  the  case 
of  some  other  borates.  It  is  self-evident  that  the  boric  acid  may  be 
estimated,  in  another  portion  of  the  salt,  by  I.,  1,  c,  or  2.  If  you 
have  to  estimate  boric  acid  in  presence  of  large  proportions  of 
alkali  salts,  make  the  fluid  alkaline  with  potassa,  evaporate  to  dry- 
ness,  extract  the  residue  with  alcohol  and  some  hydrochloric  acid, 
add  solution  of  potassa  to  strongly  alkaline  reaction,  distil  off  the 
alcohol,  and  then  proceed  as  in  I.,  1,  #,  or  2  (Auo.  STROMEYER,  loc. 
cit.). 

LuNGEf  determined  the  soda  in  boronatrocalcite  alkalimetri- 
cally,  by  dissolving  the  mineral  in  normal  nitric  acid  and  titrat- 
ing back  with  normal  soda,  till  the  tint  of  the  litmus  added  becomes 
violet. 

1).  From  Calcium. 

Dissolve  in  hydrochloric  acid  in  the  heat,  avoiding  too  large  an 
excess,  neutralize  with  ammonia  and  precipitate  with  ammonium 
oxalate  (LUNGE,  loc.  cit.). 

c.  From  almost  all  other  Bases  except  Alkalies. 

The  compounds  are  decomposed  by  boiling  or  fusing  with 
potassium  carbonate  or  hydroxide  ;  the  precipitated  base  is  filtered 
off,  and  the  boric  acid  determined  in  the  filtrate,  according  to  I.,  1, 
*  Annal.  d.  Chem.  u.  Pharm.  100,  82.  f  Ib.  138,  53. 


§  136.]  BORIC    ACID   AND   BORIC    ANHYDRIDE.  393 

d,  or  2.  If  magnesium  was  present,  a  little  of  this  is  very  likely 
to  get  into  the  filtrate,  and — if  process  L,  2,  is  employed — upon 
neutralizing  with  hydrofluoric  acid,  this  separates  an  insoluble 
magnesium  fluoride,  which  may  either  be  filtered  off  at  once,  or 
removed  subsequently,  by  treating  the  potassium  borofluoride  with 
boiling  water,  in  which  that  salt  is  soluble,  and  the  magnesium 
fluoride  insoluble. 

d.  From  the  Metallic  Oxides  of  the  Fourth,  Fifth,  and  Sixth 
Groups. 

The  metallic  oxides  are  precipitated  by  hydrogen  sulphide,  orT 
as  the  case  may  be,  ammonium  sulphide,*  and  determined  by  the 
appropriate  methods.  The  quantity  of  boric  acid  may  often  be 
inferred  from  the  loss.  If  it  has  to  be  estimated  in  the  direct  way, 
the  filtrate,  after  addition  of  solution  of  potassa  and  some  potassium 
nitrate,  is  evaporated  to  dry  ness,  the  residue  ignited,  and  the  boric 
acid  estimated  by  I.,  1,  d,  or  2.  In  cases  where  the  metal  has  been 
precipitated  by  hydrogen  sulphide  from  acid  or  neutral  solutions, 
the  boric  acid  may  also  be  determined  in  the  filtrate — in  the  absence 
of  other  acids — by  L,  1,  a  or  b  or  c-,  after  the  complete  removal  of 
the  hydrogen  sulphide  by  transmitting  carbon  dioxide  through  the 
fluid. 

e.  From  the  whole  of  the  Fixed  Ba&ic  Radicals. 

A  portion  of  the  very  finely  pulverized  substance  is  weighedr 
put  into  a  capacious  platinum  dish,  and  digested  with  a  sufficient 
quantity  of  hydrofluoric  acid  (which  leaves  no  residue  when  evapo- 
rated in  a  platinum  dish)  ;  pure  concentrated  sulphuric  acid  is  then 
gradually  added,  drop  by  drop,  and  the  mixture  heated,  gently  at 
first,  then  more  strongly,  until  the  excess  of  the  sulphuric  acid  is 
completely  expelled.  In  this  operation  the  boric  acid  goes  off  in 
the  form  of  fluoride  of  boron  (B,O3  +  6HF  =  2BF8  +  3H,O). 
The  basic  metals  contained  in  the  residue  in  the  form  of  sulphates 
are  determined  by  the  appropriate  methods,  and  the  quantity  of 
the  boric  acid  is  found  by  difference.  It  is  of  course  taken  for 
granted  that  the  substance  is  decomposable  by  sulphuric  acid. 

*  Boric  acid  cannot  be  separated  completely  from  aluminium  by  precipitation 
of  the  hydrochloric  acid  solution  with  ammonium  sulphide  or  with  ammonium 
carbonate  (WOHLEB,  Ann.  d.  Chem.  u.  Pharm.  141, 


394  DETERMINATION.  [§  137. 


3.  OXALIC  ACID. 

I.  Determination. 

Oxalic  acid  is  either  precipitated  as  calcium  oxalate,  and  esti- 
mated after  determination  of  the  calcium  in  the  latter  as  oxide, 
carbonate,  or  sulphate;  or  the  amount  contained  in  a  compound 
is  inferred  from  the  quantity  of  solution  of  potassium  permanga- 
nate required  to  effect  its  conversion  into  carbonic  acid  ;  or  from 
the  quantity  of  gold  which  it  reduces  ;  or  from  the  amount  of  car- 
bonic acid  which  it  affords  by  oxidization. 

a.  Determination  as  Calcium  Carbonate,  <&c. 

Precipitate  with  solution  of  calcium  acetate,  added  in  moderate 
excess,  and  treat  the  precipitated  calcium  oxalate  as  directed  in 
§  103.  If  this  method  is  to  yield  accurate  results,  the  solution 
must  be  neutral  or  slightly  acid  with  acetic  acid  /  it  must  not  con- 
tain salts  of  aluminium,  chromium,  or  of  the  heavy  metals,  more 
•especially  cupric  or  ferric  salts  ;  therefore,  where  these  conditions 
do  not  exist,  they  must  tirst  be  supplied. 

b.  Determination  by  means  of  Solution  of  Potassium  Perman- 
ganate. 

Standardize  the  solution  of  potassium  permanganate,  as  directed 
§  112,  2,  a,  cc,  by  means  of  oxalic  acid  ;  then  dissolve  the  substance 
in  about  150  c.c.  water,  or  acid  and  water  (sulphuric  acid  is  the 
best  acid  to  use)  ;  add,  if  necessary,  a  further  quantity  of  sulphuric 
acid  (about  6  or  8  c.c.  strong  sulphuric  acid  should  be  present),  heat 
to  about  60°,  and  then  run  in  the  permanganate,  with  constant 
stirring,  until  the  fluid  just  shows  a  red  tint.  Knowing  the  quan- 
tity of  oxalic  acid  which  100  c.c.  of  the  standard  permanganate 
will  oxidize,  a  simple  calculation  will  give  the  quantity  of  oxalic 
acid  corresponding  to  the  c.c.  of  permanganate  used  in  the  experi- 
ment. The  results  are  very  accurate. 

c.  Determination  from  the  reduced  Gold  (H.  KOSE). 

a.  In  compounds  soluble  in  water.  Add  to  the  solution  of  the 
oxalic  acid  or  the  oxalate  a  solution  of  sodium  auric  chloride,  or 
ammonium  auric  chloride,  and  digest  for  some  time  at  a  tempera- 
ture near  ebullition,  with  exclusion  of  direct  sunlight.  Collect  the 
precipitated  gold  on  a  filter,  wash,  dry,  ignite,  and  weigh.  2  at. 


§  137.]  OXALIC   ACID.  395 

Au.  (196-71  X  2  =  393-42)  correspond  to  3  mol.  C,O3  (72  X  3  = 
216). 

ft.  In  compounds  insoluble  in  water.  Dissolve  in  the  least 
possible  amount  of  hydrochloric  acid,  dilute  with  a  very  large 
quantity  of  water,  in  a  capacious  flask,  cleaned  previously  with 
solution  of  soda ;  add  solution  of  gold  in  excess,  boil  the  mixture 
some  time,  let  the  gold  subside,  taking  care  to  exclude  sunlight, 
and  proceed  as  in  a. 

d.  Determination  as  Carbonic  Add. 

This  may  be  effected  either, 

a.  By  the  method  of  organic  analysis ;  or 

ft.  By  mixing  the  oxalic  acid  or  oxalate  with  finely  pulverized 
manganese  dioxide  in  excess,  and  adding  sulphuric  acid  to  the  mix- 
ture, in  an  apparatus  so  constructed  that  the  disengaged  CO,  passes 
off  perfectly  dry.  The  theory  of  this  method  may  be  illustrated 
by  the  following  equation  :  H,C2O4  +  MnO3  +  H,SO4  =  MnSO, 
-f-  2H,O  +  2COa.  For  the  apparatus  and  process,  I  refer  to  the 
chapter  on  the  examination  of  manganese  ores,  in  the  Special  Part 
of  this  work.  Here  I  may  remark  that  free  oxalic  acid  must  first 
be  prepared  for  the  process  by  .slight  supersaturation  with  alkali 
free  from  carbonic  acid,  and  also  that  9  parts  of  oxalic  anhydride 
(C2O3)  require  theoretically  11  parts  of  (pure)  manganese  dioxide. 
Since  an  excess  of  the  latter  substance  does  not  interfere  with  the 
accuracy  of  the  results,  it  is  easy  to  find  the  amount  to  be  added. 
The  manganese  dioxide  need  not  be  pure,  but  it  must  contain  no 
carbonate.  This  method  is  expeditious,  and  gives  very  accurate 
results,  if  the  process  is  conducted  in  an  apparatus  sufficiently  light 
to  admit  of  the  use  of  a  delicate  balance.  Instead  of  manganese 
dioxide,  potassium  chromate  may  be  used  (compare  §  130,  1,  c), 
and  instead  of  estimating  the  carbonic  acid  by  loss  it  may  be  col- 
lected by  an  absorbent  and  weighed  (§  139,  II.,  e) ;  the  latter 
method  is  always  to  be  preferred  in  the  case  of  small  quan- 
tities. 

II.  /Separation  of  Oxalic  Acid  from  the  Basic  Radicals. 
The  most  convenient  way  of  analyzing  oxalates  is,  in  all  cases, 
to  determine  in  one  portion  the  acid,  by  one  of  the  methods  given 
in  I.,  in  another  portion  the  basic  radical,  particularly  as  the  latter 
object  may  be  generally  effected  by  simple  ignition  in.  the  air, 
which  reduces  the  salt  either  to  the  metallic  state  (e.g.,  silver  oxa- 


396  DETERMINATION.  [§  138. 

late),  or  to  pure  oxide  (e.g.,  lead  oxalate),  or  to  carbonate  (e.g.,  the 
oxalates  of  the  alkalies  and  alkali-earth  metals). 

If  the  acid  and  basic  radical  have  to  be  determined  in  one  and 
the  same  portion  of  the  oxalate,  the  following  methods  may  be 
resorted  to : 

a.  The  oxalic  acid  is  determined  by  L,  c,  and  the  gold  separated 
from  the  basic  metals  in  the  filtrate  by  the  methods  given  in  Sec- 
tion V. 

J.  In  many  soluble  salts  the  oxalic  acid  may  be  determined  by 
the  method  L,  a ;  separating  the  basic  metals  afterwards  from  the 
excess  of  the  calcium  salt  by  the  methods  given  in  Section  Y. 

c.  Many  oxalates  of  metals  which  are  completely  precipitated 
"as  carbonates  or  oxides  by  excess  of  sodium  or  potassium  carbonate, 
may  be  decomposed   by   boiling  with  excess  of  these  reagents, 
metallic  oxide  or  carbonate  being  formed,  on  the  one,  and  alkali 
oxalate  on  the  other  side. 

d.  All  oxalates  of  the  metals  of  the  fourth,  fifth,  and  sixth 
groups  may  be  decomposed  with  hydrogen  sulphide  or  ammonium 
sulphide. 

§  138. 
4.  HYDROFLUORIC  ACID. 

I.  DETERMINATION. 

Free  hydrofluoric  acid  in  aqueous  solution*  is  determined  either 
with  standard  alkali  or  as  calcium  fluoride.  In  the  latter  case 
sodium  carbonate  is  added  in  moderate  excess,  then  the  solution 
being  boiled,  calcium  chloride  is  added  as  long  as  a  precipitate  con- 
tinues to  form ;  when  the  precipitate,  which  consists  of  calcium 
fluoride  and  carbonate,  has  subsided,  it  is  washed,  first  by  decanta- 
tion,  afterwards  on  the  filter,  and  dried ;  when  dry,  it  is  ignited  in 
a  platinum  crucible  (§  53) ;  water  is  then  poured  over  it  in  a  plati- 
num or  porcelain  dish,  acetic  acid  added  in  slight  excess,  the  mix- 
ture evaporated  to  dryness  on  the  water-bath,  and  heated  on  the 
latter  until  all  odor  of  acetic  acid  disappears.  The  residue,  which 
consists  of  calcium  fluoride  and  acetate,  is  heated  with  water,  the 


*  In  analyzing  fluorides  you  must  always  avoid  bringing  acid  solutions  in 
contact  with  glass  or  porcelain.  If  platinum  or  silver  dishes  of  sufficient  size  are 
not  at  hand  you  may  sometimes  use  gutta-percha  vessels,  or  glass  vessels  coated 
with  wax  or  paraffin. 


$  138.]  HYDROFLUORIC    ACID.  397 

calcium  fluoride  filtered  off,  washed,  dried,  ignited  (§  53),  and 
weighed.  As  a  control  of  the  purity  of  the  calcium  fluoride,  it  is 
well  to  convert  it  after  weighing  into  sulphate.  If  the  precipitate 
of  calcium  fluoride  and  carbonate  were  treated  with  acetic  acid, 
without  previous  ignition,  the  washing  of  the  fluoride  would  prove 
a  difficult  operation.  Presence  of  nitric  or  hydrochloric  acid  in  the 
aqueous  solution  of  the  hydrofluoric  acid  does  not  interfere  with 
the  process  (H.  ROSE). 

II.  SEPARATION  OF  FLUORINE  FROM  THE  METALS. 

1.  Fluorides  Soluble  in  Water. 

If  the  solutions  have  an  acid  reaction,  sodium  carbonate  is 
added  in  excess.  If  there  is  an  odor  of  ammonia  now,  heat  till  the 
latter  is  expelled.  If  the  sodium  carbonate  produces  no  precipitate, 
the  fluorine  is  determined  by  the  method  given  in  L,  and  the 
metals  in  the  filtrate  are  separated  from  calcium  and  sodium  by 
the  methods  given  in  Section  V.  But  if  the  sodium  carbonate  pro- 
duces a  precipitate,  the  mixture  is  heated  to  boiling,  then  filtered, 
and  the  fluorine  determined  m  the  filtrate  by  the  method  given  in 
I. ;  the  metals  are  in  the  precipitate,  which  must,  however,  first  be 
tested,  to  make  sure  that  it  contains  no  fluorine.  Neutral  solutions 
are  mixed  with  a  sufficient  quantity  of  calcium  chloride,  and  the 
mixture  heated  to  boiling  in  a  platinum  dish  or,  but  less  appropri- 
ately, in  a  porcelain  dish  ;  the  precipitate  of  calcium  fluoride  is 
allowed  to  subside,  thoroughly  washed  with  hot  water  by  decanta- 
tion,  transferred  to  the  filter,  dried,  ignited,  and  weighed.  The 
basic  metals  in  the  filtrate  are  then  separated  from  the  excess  of  the 
calcium  salt  by  the  usual  methods.  That  the  basic  metals  may  be 
determined  also  in  separate  portions  by  the  methods  given  in  2  #, 
need  hardly  be  stated. 

2.  Insoluble  Fluorides. 

a.  Decomposition  l>y  Sulphuric  Add  (Indirect  Estimation  of 
the  Fluorine). 

a.  Anhydrous  Compounds. 

The  finely  pulverized  and  weighed  substance  is  heated  for  some 
time  with  pure  concentrated  sulphuric  acid,  and  finally  ignited  until 
the  free  sulphuric  acid  is  completely  expelled.  In  the  presence 
of  alkalies,  ammonium  carbonate  'must  be  added  during  the  igni- 
tion. The  residuary  sulphate  is  weighed,  and  the  metal  contained 
in  it  calculated  ;  the  fluorine  is  estimated  by  loss.  In  cases  where 


398  DETERMINATION.  [§  138. 

we  have  to  deal  with  a  metal  whose  sulphate  gives  off  part  of  the 
sulphuric  acid  upon  ignition,  or  where  the  residue  contains  several 
metals,  it  is  necessary  to  subject  the  residue  to  analysis  before  this 
calculation  can  be  made.  In  the  case  of  many  compounds,  for 
instance  of  aluminium  fluoride  (which  after  ignition  requires  pro- 
longed heating  with  sulphuric  acid  for  its  decomposition),  long 
continued  strong  ignition  does  not  leave  the  sulphate,  but  the  oxide 
in  a  pure  state.  Topaz  (a  silicate  of  aluminium  in  isomorphous 
mixture  with  aluminium  silicofluoride)  is  not  decomposed  by  boil- 
ing sulphuric  acid,  but  it  is  decomposed  by  fusion  with  potassium 
disulphate. 

ft.  Hydrated  Fluorides. 

A  sample  of  the  substance  is  heated  in  a  tube. 

aa.  The  Water  expelled  does  not  redden  Litmus  Paper.  The 
water  is  determined  by  ignition ;  the  fluorine  and  metal  as  directed 
in  a,  a. 

lib.  The  Water  expelled  has  an  acid  reaction.  The  substance  is 
treated  with  sulphuric  acid  as  directed  in  #,  a,  to  determine  the 
metal  on  the  one  hand,  and  the  water  -|-  fluorine  on  .the  other. 
Another  weighed  portion  is  then  mixed,  in  a  small  retort,  with  about 
6  parts  of  recently  ignited  lead  oxide ;  the  mixture  is  covered  with 
a  layer  of  lead  oxide,  the  retort  weighed,  and  the  water  expelled 
by  the  application  of  heat,  increased  gradually  to  redness.  No 
hydrofluoric  acid  escapes  in  this  process.  The  weight  of  the  expelled 
water  is  inferred  from  the  loss.  The  first  operation  having  given 
us  the  water  -\-  fluorine,  and  the  second  the  water  alone,  the  dif- 
ference is  consequently  the  fluorine. 

b.  Decomposition  ~by  Fusion  with  Alkali  Carbonates. 

Many  insoluble  fluorides,  aluminium  fluoride  for  instance,  may 
be  completely  decomposed  by  fusion  with  alkali  carbonate  alone ; 
others,  such  as  calcium  fluoride,  require  the  addition  of  silicic  acid. 
In  the  first  case  the  fluorine  is  estimated  in  the  aqueous  solution  of 
the  fusion  according  to  I.,  in  the  latter  according  to  §  166,  5.  The 
temperature  must  not  be  too  high,  or  some  alkali  fluoride  may  be 
lost. 

3.    Fluorides  completely   Decomposable   by  Sulphuric 
Acid. 

As  might  be  inferred  from  2,  almost  all  fluorides  are  decom- 
posed by  heating  with  sulphuric  acid  with  evolution  of  hydroflu- 


§  138.]  HYDROFLUORIC    ACID.  399 

oric  acid.  If  silica  or  silicate  is  added  to  the  fluoride  in  sufficient 
quantity,  silicon  fluoride  and  water  escape  instead  of  hydrofluoric 
acid:  SiO,  +  4HF  =  SiF4  +  2H.O. 

On  this  reaction  methods  of  determining  fluorine  have  been 
based.  In  the  first,  which  I  published  some  years  ago,*  the  fluor- 
ide of  silicon  is  determined  by  increase  of  weight  of  absorption 
tubes ;  this  I  believe  to  be  in  many  cases  the  only  method  which 
is  applicable,  and  when  carefully  carried  out  yields  ttie  most  accu- 
rate results. 

a.  Estimation  by  Absorption  of  the  evolved  Fluoride  Silicon. 

The  method  as  here  given  is  the  result  of  a  long  series  of  experi- 
ments ;  the  conditions  laid  down  must  be  most  carefully  attended 
to.  The  fluoride  must  be  in  the  finest  powder.  As  silicic  acid  we 
use  finely  powdered  quartz,  wrhich  has  been  ignited  in  the  air  to 
destroy  any  organic  admixture.  The  sulphuric  acid  should  have  a 
sp.  gr.  of  1  •  848,  it  must  be  colorless  and  free  from  oxides  of  nitro- 
gen and  sulphurous  acid.  The  gasometer  must  be  filled  with  clean 
air,  and  not  with  air  from  the  laboratory,  for  any  dust  of  organic 
matter,  traces  of  coal  gas,  &c.,  would  interfere  with  the  accuracy  of 
the  result.  The  apparatus  required  is  shown  fig.  57.  A  contains 
atmospheric  air,  b  is  half  filled  with  sulphuric  acid,  c  contains  soda- 
lime  with  plugs  of  cotton, d pieces  of  glass  moistened  with  sulphuric 
acid.  The  air  is  thus  freed  from  carbonic  acid  and  suspended  mat- 
ter, and  dried  by  sulphuric  acid  (p.  61).  e  is  the  decomposing  flask  ; 
it  has  a  capacity  of  about  250  c.c.  f  is  half  filled  with  sulphuric 
acid ;  its  cork,  which  should  not  fit  air-tight,  bears  a  thermometer 
wThose  bulb  dips  into  the  acid,  e  andy  should  be  so  placed  on  the 
iron  plate  that  the  temperature  in  both  may  be  equal,  g  is  empty ; 
h  contains  fused  calcium  chloride  in  the  first  limb,  and  pumice 
impregnated  with  anhydrous  cupric  sulphate  in  the  second.  These 
U-tubes  serve  to  retain  the  small  amount  of  sulphuric  acid  and  the 
hydrochloric  acid  which  may  accompany  it.  The  calcium  chloride 
and  the  cupric  sulphate  must  both  be  anhydrous,  or  they  will 
decompose  and  retain  silicon  fluoride.  a,  &,  and  I  are  the  weighed 
absorption  tubes;  they  are  10  or  12  cm.  high,  and  about  12  mm. 
wide,  i  contains  in  the  first  limb  pumice  moistened  with  water 
between  plugs  of  cotton,  in  the  bend  and  half  of  the  second  limb  soda- 
lime,  in  the  upper  half  of  the  second  limb  fused  calcium  chloride 


*Zeitschr.  f.  anal.  Chem.  5,  190. 


400 


DETERMINATION. 


[§138. 


between  pings  of  cotton.  The  tube  after  being  charged  weighs  about 
40  or  50  grm.     ~k  completes  the  absorption ;  it  is  filled  half  with 


soda-lime  and  half  with  fused  calcium  chloride.  I  takes  up  again 
the  small  amount  of  water  carried  away  from  i  and  &;  the  bend  is 
filled  with  pieces  of  glass  moistened  with  sulphuric  acid.  These 


§  138.]  HYDROFLUORIC    ACID.  401 

absorption  tubes  retain  the  silicon  fluoride,  the  carbonic  acid  which 
may  be  possibly  evolved  from  the  soda-lime  by  hydrofluosilicic  acid, 
and  the  aqueous  vapor ;  and  the  air  escapes  through  the  unweighed 
guard  tube  m  into  the  atmosphere.  The  latter  contains  in  the  first 
limb  calcium  chloride,  in  the  second  soda-lime.  The  flexible  con- 
nections should  not  be  long,  and  should  be  washed  and  dried 
before  use. 

When  the  apparatus  has  been  tested  and  found  air-tight,  place 
the  weighed  and  very  finely  divided  substance  in  e.  The  substance 
should  be  free  from  carbonic  acid,  and  the  quantity  taken  should 
give  not  less  than  -1  grm.  silicon  fluoride  if  possible.  Add  for 
every  part  of  fluoride  supposed  to  be  present  10  or  15  parts  of  finely 
powdered  quartz  (previously  strongly  ignited  in  the  air),  and  then 
40  or  50  c.c.  pure  concentrated  sulphuric  acid.  Connect  e,  on  the 
one  hand,  with  d,  and,  on  the  other,  with  g,  and  pass  a  moderate 
current  of  air,  which  should  enter  the  fluid  in  the  decomposing  flask 
from  the  bottom.  Heat  the  iron  plate,  shake  e  frequently  and  raise 
the  temperature  very  gradually,  till  the  thermometer  in  f  indicates 
150°  to  160°.  The  commencement  of  the  decomposition  shows 
itself  not  only  by  the  appearance  of  bubbles  of  gas  in  the  fluid, 
more  particularly  at  the  edge,  but  also  by  the  separation  of  hydrated 
silica  in  i.  The  bubbles  of  gas  will  disappear  on  shaking  the  fluid  ; 
as  soon  as  they  cease  to  form  again  remove  the  lamp ;  the  time 
usually  occupied  in  the  decomposition  is  one  hour  for  small  quantities 
of  fluoride  ( •  1  grm.),  two  or  three  hours  for  large  quantities  (1  grm.). 
After  a  while  shut  off  the  current  of  air,  remove  the  weighed  tubes 
2,  &,  and  /,  and  during  the  weighing  of  these  connect  h  with  m  by 
means  of  a  glass  tube.  After  weighing  replace  2",  &,  and  /,  heat 
again  to  150°  or  160°,  and  pass  the  air  again  for  half  an  hour  or  an 
hour,  weighing  *,  &,  and  I  again.  If  any  alteration  of  weight  has 
occurred,  the  process  must  be  continued. 

The  increase  in  weight  of  the  absorption  tubes  after  deducting 
-  001  grm.  for  every  hour  during  which  the  air  has  been  passing 
(i.e.,  for  every  6  litres  of  air)  represents  the  amount  of  silicon 
fluoride.  The  small  correction  is  necessary  because  air,  even  when 
it  comes  in  contact  only  with  short  washed  pieces  of  india-rubber, 
always  gives  traces  of  sulphurous  and  carbonic  acid  when  passed 
through  hot  concentrated  sulphuric  acid.  The  results  thus  obtained 
are  very  satisfactory,  and  differ  from  the  truth  at  the  most  by  a 
few  milligrammes. 


402  DETERMINATION.  [§  130. 

b.  Other  methods  of  Estimating  the  Silicon  Fluoride  expelled. 

a.  Method  of  WOHLEE.  Only  applicable  when  the  substance 
is  readily  decomposed  by  sulphuric  acid,  and  the  amount  of  fluorine 
is  large.  Transfer  the  very  finely  divided  substance,  if  necessary, 
intimately  mixed  with  10  or  15  parts  of  ignited  quartz  powder,  to  a 
small  flask,  add  pure  sulphuric  acid,  close  quickly  with  a  cork  fitted 
with  a  small  tube  filled  with  fused  calcium  chloride  (or  better  still, 
half  with  fused  calcium  chloride  and  half  with  anhydrous  cupric 
sulphate  on  pumice),  weigh  the  whole  apparatus  as  quickly  as  pos- 
sible, warm  it  till  no  more  fumes  of  silicon  fluoride  escape,  remove 
the  last  particles  of  gas  in  the  apparatus  by  an  air  pump,  allow  to 
cool,  and  weigh.  The  loss  of  weight  indicates  the  amount  of  silicon 
fluoride. 

ft.  [S.  L.  PENFIELD*  determines  the  amount  of  expelled  silicon 
fluoride  by  an  indirect  volumetric  method  ;  viz. :  by  passing  it  into 
a  solution  of  potassium  chloride,  and  titrating  the  hydrochloric  acid 
which  is  set  free  with  standard  ammonia  solution.  3SiF4  -f-  2 
H20  =  2  H2F2SiF4  +  Si02  and  H2F2SiF4  +  2KC1  =  (KF)2SiF4  +  2 
HC1.  Two  mol.  HC1  thus  liberated  correspond  to  six  at.  F. 

'  The  process  of  decomposing  the  fluorine  compound  is  conducted 
as  in  «,  and  the  same  apparatus  may  be  used  except  that  the  four 
last  U-tubes  *,  &,  /,  m,  are  replaced  by  two  larger  U-tubes  for  hold- 
ing the  solution  of  potassium  chloride. 

The  aqueous  solution  of  KC1  is  mixed  with  an  equal  volume  of 
alcohol  to  effect  complete  precipitation  of  the  hydroflupsilicic  acid. 
The  titration  may  be  either  effected  directly  in  U-tubes  (the  second 
of  which  will  contain  but  a  very  small  quantity  of  acid)  or  after 
transferring  to  a  beaker  and  rinsing  the  tubes  with  alcohol  and 
water.  Care  must  be  taken  to  loosen  and  break  up  the  silicic  acid 
and  to  have  at  least  half  of  the  final  volume  at  the  end  of  the  titra- 
tion consist  of  alcohol.  Kesults  given  by  the  author  (loc.  cit.)  very 
satisfactory.] 

*  American  Chem.  Journ.  i.  p.  27. 


§  139.]  CARBONIC    ACID.  .  403 

Fourth  Division  of  the  First  Group  of  the  Adds. 

CARBONIC  ACID SILICIC  ACID. 

§  139. 
1.  CARBONIC  Aero. 

I.  Determination. 

a.  In  a  mixture  of  Gases. 

After  thoroughly  drying  the  gases  with  a  ball  of  calcium  chloride, 
or  saturating  with  moisture  (§  16),  measure  them  accurately  in  a 
graduated  tube  over  mercury,  insert  a  ball  of  hydrate  of  potassa,* 
cast  on  a  platinum  wire  in  a  pistol  bullet-mould,  take  care  that  the 
end  of  the  platinum  wire  remains  under  the  surface  of  the  mercury, 
leave  in  the  tube  for  24  hours,  or  until  the  volume  of  the  gas  ceases 
to  show  further  diminution ;  withdraw  the  ball,  and  measure  the 
gas  remaining,  reinsert  the  same  or  a  fresh  ball  of  potassa,  and 
repeat  till  no  further  absorption  takes  place.  The  carbonic  acid 
gas  is  inferred  from  the  difference,  provided  the  gaseous  mixture 
contained  no  other  gas  liable  to  absorption  by  potassa  (compare 
§§  12-16).  In  very  accurate  analyses  you  must  bear  in  mind 
that  carbonic  acid  does  not  exactly  follow  the  law  of  MARIOTTE. 

If  the  amount  of  carbonic  acid  is  very  small,  this  process  does 
not  yield  sufficiently  accurate  results.  In  such  cases  one  of  the. 
methods  recommended  in  "The  Analysis  of  Atmospheric  Air" 
should  be  employed.  Several  kinds  of  special  apparatus  are  in  use 
for  the  estimation  of  carbonic  acid  in  coal  gas  and  for  the  purposes 
of  sugar  works.  I  may  mention  those  proposed  by  F.  RuDORFFf 
and  LEHMANN  and  H.  WAHLERTJ:  for  the  first  purpose,  and  by  C. 
SCHEIBLER§  and  C.  STAMMERJ!  for  the  second.  Besides  these  volu- 
metric methods  the  gravimetric  processes  given  by  myself  for  the 
analysis  of  gaseous  mixtures^  may  often  be  used  with  great  advan- 
tage. 

*  The  ordinary  hydrate  is  not  adapted  for  the  purpose.  It  should  be  fused 
with  a  quarter  of  its  weight  of  water  in  a  platinum  crucible. 

f  Pogg.  Annal.  125,  71.  f  Zeitschr.  f.  anal.  Chem.  7,  58. 

§  Dingler's  polyt.  Journ.  183,  306.  |  Ib.  102,  368. 

11  Zeitschr.  f.  anal.  Chem.  3,  343. 


404  DETERMINATION.  [§  139. 

J.  In  Aqueous  Solution. 

a.  WITH  CALCIUM  HYDROXIDE. 

Into  a  flask,  holding  about  300  c.c.,  put  2'5  to  3  grin,  calcium 
hydroxide  perfectly  free  from  carbonate.*  Provide  the  flask  with 
a  good  india-rubber  stopper,  tare  or  weigh  exactly,  add  the  car- 
bonic acid  water  with  gentle  agitation  till  the  flask  is  two  thirds  or 
three  quarters  fall,  and  close  at  once. 

In  adding  the  carbonic  acid  water  every  care  must  of  course  be 
taken  to  guard  against  loss  of  carbonic  acid.  If  the  water  flows 
from  a  pipe,  it  is  allowed  simply  to  run  in.  If  it  is  in  a  jug  or 
bottle,  cool  it  to  4°,  and  transfer  the  quantity  required  with  a 
syphon.f  If  the  water  is  in  a  basin  or  well,  provide  the  flask 
with  a  stopper  in  which  two  glass  tubes  are  inserted,  one  a  few 
inches  long,  pushed  down  only  to  the  lower  surface  of  the  stopper, 
the  other  extending  through  the  stopper  a  short  distance  into  the 
flask,  but  only  to  the  upper  surface  of  the  stopper.  Sink  the  flask 
into  the  water,  and  water  will  enter  one  tube  and  air  escape  through 
the  other.  Water  which  is  not  very  rich  in  free  carbonic  acid  may 
be  removed  from  the  basin  or  well  by  a  plunging-syphon. 

Now  weigh  the  flask  with  its  stopper  again,  and  you  will  find 
the  quantity  of  water  taken.  No  way  of  measuring  the  water  is 
so  accurate  in  retaining  all  the  carbonic  acid  and  in  giving  the 
quantity  of  water  taken. 

If  there  is  much  interval  between  the  mixing  of  the  water  and 
the  lime  and  the  estimation  of  the  carbonic  acid  in  the  precipitate, 
the  calcium  carbonate,  which  is  at  first  amorphous,  passes  spontane- 
ously into  the  crystalline  condition ;  but  if  the  carbonic  acid  is  to 
be  determined  soon  after  the  mixing,  heat  for  some  time  on  the 
water-bath,  raising  the  stopper  occasionally,  in  order  to  hasten  the 
change  of  the  calcium  carbonate.  Now,  without  disturbing  the 
precipitate,  filter  the  clear  fluid  through  a  small  plaited  filter, 
which  will  take  a  very  short  time,  throw  the  filter  at  once  into  the 
flask  containing  the  precipitate  and  the  rest  of  the  fluid,  and  pro- 
ceed according  to  II.,  e.  This  process  has  been  in  use  for  10  years 
in  my  laboratory  for  all  mineral  water  analyses ;  it  is  extremely 


*  This  is  prepared  by  slaking  freshly  burnt  lime  with  water  in  such  a  man- 
ner that  the  hydrate  obtained  appears  dry  and  pulverulent.  It  is  preserved  in 
small  bottles,  the  corks  or  stoppers  of  which  are  covered  with  sealing  wax. 

f  If  the  water  is  poured  directly  from  the  jug  into  the  flask,  carbonic  acid 
gas  is  very  likely  to  get  into  the  latter  as  well  as  the  water. 


§  139.  j  CARBONIC  ACID.  405 

simple,  and  gives  excellent  results.*  If  the  water  contains  alkali 
carbonate,  put  a  quantity  of  calcium  chloride  sufficient  to  decom- 
pose the  alkali  carbonate  with  the  lime  in '  the  flask  before  adding 
the  water. 

ft.  AFTER  PETTEXKOFER.f 

The  principle  of  this  simple  and  expeditious  process  consists  in 
mixing  the  carbonic  acid  water  with  a  measured  quantity  of  stand- 
ard lime  water  (or,  under  certain  circumstances,  baryta  water)  in 
excess.  After  complete  separation  of  the  calcium  or  barium  carbo- 
nate, the  excess  of  calcium  or  barium  in  the  fluid  is  determined  in 
an  aliquot  part  by  means  of  standard  solution  of  oxalic  acid ;  the 
difference  gives  the  calcium  or  barium  precipitated  by  the  carbonic 
acid,  and  consequently  the  amount  of  the  latter  present. 

If  a  water  contains  only  free  carbonic  acid,  the  analyst  has  only 
to  bear  in  mind — if  lime  water  is  employed — that  the  calcium  car- 
bonate formed  is  at  first,  as  long  as  it  remains  amorphous,  very 
perceptibly  soluble  in  water,  to  which  it  communicates  an  alkaline 
reaction.  Hence  the  unprecipitated  lime  in  the  fluid  cannot  be 
estimated  till  the  calcium  carbonate  has  separated  in  the  crystalline 
form,  which  takes  8  or  10  hours,  unless  the  mixture  is  warmed  to 
70°  or  80°.  On  this  account  it  is  generally  best  to  use  baryta 
water  (see  "  Analysis  of  Atmospheric  Air"). 

If,  on  the  contrary,  a  water  contains  an  alkali  carbonate  or  any 
other  alkali  salt  whose  acid  would  be  precipitated  by  lime  or  baryta, 
a  neutral  solution  of  calcium  or  barium  chloride  must  first  be  added 
to  decompose  the  same.  This  addition,  too,  prevents  any  incon- 
venience arising  from  the  presence  of  free  alkali  in  the  lime  or 
baryta  water,  or  of  magnesium  carbonate  in  the  carbonic  acid 
water;  this  inconvenience  consists  in  the  fact  that  oxalate  of  an 
alkali  or  of  magnesium  enters  into  double  decomposition  with  cal- 
cium carbonate  (which  is  seldom  entirely  absent  from  the  fluid  to 
be  analyzed),  forming  calcium  oxalate  and  carbonate  of  the  alkali 
or  of  magnesium,  which  latter  will  of  course  again  take  up  oxalic 
acid. 

In  the  presence  of  magnesium  salts  in  the  carbonic  acid  water, 
in  order  to  avoid  the  precipitation  of  the  magnesium,  a  little 
ammonium  chloride  must  also  be  added,  but  in  this  case  heat  must 

*  Zeitschr.  f.  anal.  Chem.  2,  49  and  341. 

f  BDCHXER'S  neues  Repert.  10,  1;  Journ.  f.  prakt.  Chem.  82,  32;  Annal.  d. 
Chem.  u.  Pharm.  ii.,  Supplementb.  1 ;  Zeitschr.  f.  anal.  Chem.  1,  92. 


406  DETERMINATION.  [§  139. 

not  be  applied  to  induce  the  calcium  carbonate  to  become  more 
quickly  crystalline,  as  ammonia  would  be  thereby  expelled. 

In  making  the  determination  the  first  thing  to  be  done  is  to 
ascertain  the  relation  between  the  lime  or  baryta  water  and  a 
standard  solution  of  oxalic  acid.  PETTENKOFER  makes  the  latter 
solution  by  dissolving  2'8636  grm.  pure  uneffloresced  dry  crystal- 
lized oxalic  acid  to  1  litre ;  1  c.c.  of  this  is  equivalent  to  1  mgrm. 
carbonic  acid.  The  lime  water  is  standardized  as  follows  :  Measure 
45  c.c.  into  a  little  flask  which  can  be  closed  by  the  thumb,  and 
then  run  in  from  the  burette  the  solution  of  oxalic  acid  till  the 
alkaline  reaction  has  just  vanished.  During  the  operation  the 
flask  is  closed  with  the  thumb  and  gently  shaken.  The  end  is 
attained  as  soon  as  a  drop  taken  out  with  a  glass  rod  and  applied  to 
delicate  turmeric  paper*  produces  no  brown  ring.  The  first 
experiment  is  a  rough  one,  the  second  should  be  exact. 

The  analysis  of  a  carbonic  acid  water  (a  spring  water,  for 
instance)  is  performed  by  transferring  100  c.c.  to  a  dry  flask,  add- 
ing 3  c.c.  of  a  neutral  and  nearly  saturated  solution  of  calcium  or 
barium  chloride,  and  2  c.c.  of  a  saturated  solution  of  ammonium 
chloride,  then  45  c.c.  of  the  standard  lime  or  baryta  water;  close 
the  flask  with  an  india-rubber  stopper,  shake  and  allow  to  stand  12 
hours.  The  fluid  contents  of  the  flask  measure  consequently  150 
c.c.  From  the  clear  fluidf  take  out  by  means  of  a  pipette  two  por- 
tions of  50  c.c.  each,  and  determine  the  free  lime  or  baryta  by 
means  of  oxalic  acid,  in  the  first  portion  approximately,  in  the 
second  exactly.  Multiply  the  c.c.  used  in  the  last  experiment  by 
3  and  deduct  the  product  from  the  c.c.  of  oxalic  acid  which  corre- 
spond to  45  c.c.  of  lime  or  baryta  water.  The  difference  shows  the 
lime  or  baryta  precipitated  by  carbonic  acid,  each  c.c.  corresponds 
to  1  mgrm.  carbonic  acid. 


*  For  the  preparation  of  this  bibulous  paper  should  be  used,  the  ash  of  which 
is  free  from  carbonate  of  lime.  Swedish  filtering-paper  answers  best.  J.  GOTT- 
LIEB (Journ.  f.  prakt.  Chem.  107,  488;  Zeitschr.  f.  anal.  Chem.  9,  251)  prefers 
aqueous  tincture  of  litmus,  prepared  from  litmus  first  exhausted  with  spirit  and 
used  in  a  very  dilute  state.  E.  SCHULZE  and  M.  MARCKER  (Zeitschr.  f.  anal. 
Chem.  9,  334)  employ  corallin  or  rosolic  acid,  which  they  say  is  specially  adapted 
for  Ihe  purpose.  The  alcoholic  solution  is  cautiously  neutralized  with  potash, 
and  a  drop  or  two  of  this  tincture  is  added.  F.  SCHULZE  (Zeitschr.  f.  anal.  Chem. 
9,  292)  recommends  spirituous  tincture  of  turmeric. 

f  It  is  not  admissible  to  use  a  filter  (A.  MULLER,  Zeitschr.  f  anal.  Chem  1 
84). 


§  139.]  CARBONIC    ACID.  407 

The  method  is  convenient  and  good  ;  it  is  especially  to  be 
recommended  for  dilute  carbonic  acid  water.  When  calcium  sul- 
phate or  carbonate  is  present,  as  is  almost  always  the  case  in  spring 
water,  you  must  always  before  titrating  await  the  conversion  of  the 
amorphous  calcium  carbonate  to  the  crystalline  state,  even  if  baryta 
water  is  used  (K.  KNAPP*)..  Baryta  water  therefore  possesses  no 
advantages  over  lime  water  for  the  analysis  of  spring  waters. 

II.   Separation   of   Carbonic   Acid  from   the   Basic 
Radicals,  and  its  Estimation  in  Carbonates. 

a.  Estimation  in  Normal  Alkali  Carbonates  and  Alkali-earth 
Carbonates. 

If  the  salts  are  unquestionably  normal  carbonates,  and  there  is 
no  other  salt  with  power  to  neutralize  an  acid  present,  we  may 
determine  the  quantity  of  the  basic  radical  by  the  alkalimetric 
method  (§§  196,  198),  and  calculate  the  amount  of  CO,  necessary 
to  form  with  it  normal  carbonate. 

b.  Separation  from  Basic  Metals  in  Salts  which  upon  ignition 
readily  and  completely  yield  their  Carbonic  Acid. 

Such  are,  for  instance,  the  carbonates  of  zinc,  cadmium,  lead, 
copper,  magnesium,  &c. 

a.  Anhydrous  Carbonates. — Ignite  the  weighed  substance,  in  a 
platinum  crucible  (cadmium  and  lead  carbonates  in  a  porcelain 
crucible),  until  the  weight  of  the  residue  remains  constant.  The 
results  are,  of  course,  very  accurate.  Substances  liable  to  absorb 
oxygen  upon  ignition  in  the  air  are  ignited  in  a  bulb-tube,  through 
which  a  stream  of  dry  carbon  dioxide  gas  is  conducted.  The  car- 
bonic acid  is  inferred  from  the  loss. 

ft.  Hydritted  Carbonates. — The  substance  is  ignited  in  a  bulb- 
tube  through  which  dried  air  or,  in  presence  of  oxidizable  sub- 
stances, carbon  dioxide  is  transmitted,  and  which  is  connected  with 
a  calcium  chloride  tube,  by  means  of  a  dry,  close-fitting  cork. 
During  the  ignition,  the  posterior  end  of  the  bulb-tube  is,  by 
means  of  a  small  lamp,  kept  sufficiently  hot  to  prevent  the  con- 
densation of  water  in  it,  care  being  taken,  however,  to  guard  against 
burning  the  cork.  The  loss  of  weight  of  the  tube  gives  the  amount 
of  the  water  -f-  the  carbonic  acid ;  the  increase  of  weight  gained  by 
the  calcium  chloride  tube  gives  the  amount  of  the  water,  and  the 
difference  accordingly  that  of  the  carbonic  acid.  A  somewhat 

*  Annal.  d.  Chem.  u.  Pharm.  158,  112;  Zeitschr.  f.  anal.  Chem.  10,  861. 


408  DETERMINATION.  [§  139, 

wide  glass  tube  may  also  be  put  in  the  place  of  the  bulb-tube,  and 
the  substance  introduced  into  it  in  a  little  boat,  which  is  weighed 
before  and  after  the  operation. 

c.  Separation  from  all  fixed  Basic  Radicals,  without  exception, 
in  Anhydrous  Carbonates. 

Fuse  vitrified  borax  in  a  weighed  platinum  crucible,  allow  to 
cool  in  the  desiccator,  weigh,  then  transfer  the  well-dried  substance 
to  the  crucible  and  weigh  again.  The  weights  of  both  carbonate 
and  borax  are  thus  ascertained.  They  should  be  in  about  the  pro- 
portion of  1  :  4-.  Heat  is  then  applied,  which  is  gradually  increased 
to  redness,  and  maintained  at  this  temperature  until  the  contents 
of  the  crucible  are  in  a  state  of  calm  fusion.  The  crucible  is  now 
allowed  to  cool,  and  weighed.  The  loss  of  weight  is  carbonic  acid. 
The  results  are  very  accurate  (SCHAFFGOTSCH). 

I  must  add  that  borax-glass  may  be  kept  in  a  state  of  fusion  at 
a  red  heat  for  J  to  \  an  hour  without  the  occurrence  of  any  vola- 
tilization, but  that  at  a  white  heat  (by  igniting  over  the  gas-bel- 
lows), even  in  a  few  minutes,  it  suffers  a  decided  loss.*  A  few 
bubbles  of  carbonic  acid  remaining  in  the  fusing  mass  are  without 
any  influence  on  the  result. 

Instead  of  vitrilied  borax  fused  potassium  dichromate  may  be 
used,  in  the  proportion  of  5  to  1  of  the  carbonate  (H.  RosEf).  The 
heat  applied  in  this  case  must  be  low,  and  great  caution  must  be 
used,  or  the  dichromate  will  lose  weight  of  itself.;):  The  carbonic 
acid  may  be  expelled  from  alkali  carbonates,  by  strong  ignition 
with  ignited  silica  (H.  EOSE§). 

d.  Separation    by   decomposition   with   Acids.      (Estimation 
from  the  loss  of  weight.) 

tv.   Carbonates  of  metals  which  form  Soluble  Salts  with 
Sulphuric  Acid. 

The  process  is  conducted  in  the  apparatus  illustrated  by  fig.  58. 
The  size  of  the  flask  depends  upon  the  capacity  of  the  balance. 
B  may  be  smaller  than  A.  The  tube  a  is  closed  at  b  with  a  little  wax 
ball,  or  a  small  piece  of  india-rubber  tube,  stopped  with  half  an  inch 
of  rod ;  the  other  end  of  the  tube  a  is  open,  as  are  also  both  ends 
of  c  and  d.  The  flask  B  is  nearly  half  filled  with  concentrated 
sulphuric  acid,  free  from  oxides  of  nitrogen  and  sulphurous  acid. 


*  Zeitschr.  f.  anal.  Chem.  1,  65.  f  Pogg.  Annal.  116,  131. 

\  Zeitschr.  f.  anal.  Chem,  1,  188.  §  Pogg.  Annal.  116,  686. 


§  139.J  CAKBONIC   ACIB.  409- 

The  tubes  must  fit  air-tight  in  the  corks,  and  the  latter  equally  *o 
in  the  flasks.  The  weighed  substance  is  put  into  A  ;  this  flask  is 
then  filled  about  one  third  with  water,  the  cork  properly  inserted, 
and  the  apparatus  tared  on  the  balance.  A  few  bubbles  of  air 
are  now  sucked  out  of  d,  by  means  of  an  india-rubber  tube.  This 
serves  to  rarefy  the  air  in  A  also,  and  causes  the  sulphuric  acid  in 
B  to  ascend  in  the  tube  c.  The  latter  is  watched  for  some  time, 
to  ascertain  whether  the  column  of  sulphuric  acid  in  it  remains 
stationary,  which  is  a  proof  that  the  apparatus  is  air-tight.  Air  is 
then  again  sucked  out  of  d,  which  causes  a  portion  of  the  sulphuric 
acid  to  flow  over  into  A.  The  carbonate  in  the  latter  flask  is 
decomposed  by  the  sulphuric  acid,  and  the  liberated  carbonic  acid, 
completely  dried  in  its  passage  through  the  sulphuric  acid  in  B9 
escapes  through  d.  When  the  evolu- 
tion of  the  gas  slackens  a  fresh  portion 
of  sulphuric  acid  is  made  to  pass  over 
into  A.  by  renewed  suction  through 
d ;  the  operation  being  repeated  until 
the  whole  of  the  carbonate  is  decom- 
posed. A  more  vigorous  suction  is 
now  applied,  to  make  a  large  amount 
of  sulphuric  acid  pass  over  into  A, 
whereby  the  contents  of  that  flask  are 
considerably  heated ;  when  the  evolu- 
tion of  gas  bubbles  has  completely 

.,  .  -,         -,  FIG.  58. 

ceased,  the  stopper  on  a  is  opened,  and 

suction  applied  to  d,  until  the  air  sucked  out  tastes  no  longer  of 
carbonic  acid.*  When  the  apparatus  is  quite  cold  it  is  replaced 
upon  the  balance,  and  the  equilibrium  restored  by  additional  weights. 
The  sum  of  the  weights  so  added  indicates  the  amount  of  carbonic 
acid  originally  present  in  the  substance. 

If  the  flasks  A  and  B  are  selected  of  small  size,  the  apparatus 
may  be  so  constructed  that,  together  with  the  contents,  it  need  not 
weigh  above  TO  grammes,  admitting  thus  of  being  weighed  on  a 
delicate  balance.  The  results  obtained  by  the  use  of  this  apparatus, 
first  suggested  by  WILL  and  myself,  are  very  accurate,  provided 
the  quantity  of  the  carbonic  acid  be  not  too  trifling.  Various 

*  In  accurate  experiments,  it  is  advisable  to  connect  the  end  b  of  the  tube  a 
with  a  calcium  chloride  tube  during  the  process  of  suction,  and  to  use  an  aspira- 
tor or  hydraulic  air-pump  instead  of  the  mouth. 


410  DETERMINATION".  [§  139. 

modifications  of  the  apparatus  have  been  proposed,  principally  in 
order  to  make  it  lighter. 

If  sulphites  or  sulphides  are  present,  together  with  the  carbon- 
ates, their  injurious  influence  is  best  obviated  by  adding  to  the 
carbonate  solution  of  normal  potassium  chromate  in  more  than 
sufficient  quantity  to  effect  their  oxidation.  If  chlorides  are  pres- 
ent, in  order  to  prevent  the  evolution  of  hydrochloric  acid,  add  to 
the  evolution  flask  a  sufficient  quantity  of  silver  sulphate  in  solu- 
tion, or  connect  the  exit  tube  d  with  a  small  prepared  U-tube, 
which  is,  of  course,  first  tared  with  the  apparatus,  and  afterwards 
weighed  with  it.  This  U-tube  is  prepared — in  accordance  with  the 
happy  proposal  of  STOLBA — by  filling  with  fragments  of  pumice 
which  have  been  boiled  with  an  excess  of  concentrated  solution  of 
cupric  sulphate,  till  the  air  has  been  expelled,  and  then  dried  and 
heated  to  complete  dehydration  of  the  copper  salt.  If  the  U-tube 
is  only  8  cm.  high  and  has  a  bore  of  1  cm.,  it  answers  the  purpose 
very  well.  The  outer  end  is  provided  with  a  perforated  cork  and 
short  glass  tube.  We  apply  suction  to  this  by  means  of  a  flexible 
tube,  instead  of  to  d. 

ft.  After  S.  W.  JOHNSON.*     All  Carbonates  which  dis- 
solve freely  in  cold  dilute  acid. 

The  apparatus  may  consist  of  a  light  flask  or  bottle  with  wide 
mouth  which  is  closed  by  a  soft  rubber  stopper,  through  which 
there  passes,  on  the  one  hand,  a  calcium  chloride  tube,  the  lower 
bulb  of  which  contains  cotton,  and,  on  the  other,  the  neck  of  a 
vessel  which  contains  the  dilute  acid.  This  acid  reservoir  is  so 
constructed  that  on  suitably  inclining  it,  its  contents  will  flow 
freely  into  the  flask.  For  this  purpose  the  tube  connecting  with 
the  latter  has  an  internal  diameter  of  seven  millimetres,  and  its 
extremity  is  cut  off  obliquely  ;  at  its  other  end,  the  acid  reservoir 
terminates  in  an  upturned  narrow  tube.  This  and  the  upper 
termination  of  the  calcium  chloride  tube  are  chosen  of  such  diame- 
ter that  they  fit  quite  snugly  into  short,  narrow,  and  thick-walled 
rubber  connectors  which  are  again  provided  with  glass-rod  stop- 
pers; all  these  joints  must  be  gas-tight.  In  figure  59  the  apparatus 
is  represented  in  one  third  its  proper  dimensions. 

The   weighed    substance,    in    case    of    calcium    carbonate,    e.g., 
is  placed  at  the  bottom  of  the  flask,  most  conveniently   in   the 


*  American  Journal  of  Science  and  Arts,  vol.  xlv.  iii.,  July,  1869. 


CARBONIC   ACID. 


411 


form  of  small  fragments.  The  acid  vessel  is  nearly  filled  witli 
hydrochloric  acid  of  sp.  gr.  1-1.  It  and  the  calcium  chloride  tube  are 
tightly  adjusted  to  the  neck  of  the  flask,  and  the  glass-rod  stoppers 
being  removed,  the  apparatus  is  connected  at  €  with  a  self-regulat- 
ing generator  of  washed  carbonic  acid,  and  a  rather  rapid  stream  of 
the  gas  is  transmitted  through  the  apparatus  for  15  minutes,  or 
until  the  liquid  is  saturated  and  the  air  is  thoroughly  displaced. 
Then  the  opening  at  d  is  stopped  and  afterward  the  apparatus  is 
disconnected  with  the  carbonic  acid  generator  and  stopped  at  c. 
During  these  as  well  as  the  subsequent  operations,  the  apparatus 
must  be  so  handled  that  its  temperature  shall  not  change.  It  is 
immediately  weighed.  When  removed  from  the  balance,  loosen 
the  stopper  at  d,  and,  holding  the  flask  by  a  wooden  clamp,  incline 
it  so  that  the  acid  may  flow  over  upon  the  carbonate.  The  decom- 
position should  proceed  slowly,  so  that  the 
escaping  gas  may  be  thoroughly  dried.  As 
soon  as  solution  of  the  carbonate  is  complete, 
replace  the  stopper  at  d,  and  weigh  again. 
Should  there  be  any  leak  in  the  apparatus  the 
fact  is  made  evident  by  a  slow  but  steady  loss 
of  weight,  when  it  is  brought  upon  the  balance. 
If  all  the  joints  are  sufficiently  tight,  the  weight 
remains  the  same  for  at  least  fifteen  minutes. 

When  properly  executed  the  process  gives 
extremely  accurate  results  ;  a  slight  change  of 
temperature  or  of  atmospheric  pressure  be- 
tween the  two  weighings  of  course  greatly  im- 
pairs the  results  or  renders  them  worthless. 
Since  the  apparatus  usually  rises  a  little  in 
temperature  during  the  solution  of  the  carbon- 
ate, it  is  better,  as  soon  as  the  substance  is  de- 
composed, to  stopper  the  CaCl,  tube  and  let 
the  whole  stand  fifteen  minutes,  then  to  connect  as  before  with 
the  gas-generator  and  pass  dried  COa  for  a  minute,  and  finally  to 
stopper  again  and  bring  upon  the  balance.  In  seven  analyses  of 
pure  calcite  in  quantities  ranging  from  O5  to  0'9  grm.,  the  follow- 
ing percentages  of  carbonic  acid  were  obtained,  viz. :  44*07,  44-07, 
43-98,  44-01,  44-04,  44-11,  44-16 ;  calculation  requires  44-00. 

In  case  of  alkali-carbonates  which  absorb  carbonic  acid  gas,  it  is 
necessary  to  modify  the  apparatus.      Instead   of   the    light   flask, 


FIG.  59. 


412  DETERMINATION.  [§  139. 

we  may  employ  a  small  bottle  of  thick  glass  and  wider  mouth,  and 
a  thrice  perforated  rubber  stopper.  Through  the  third  orifice  pass 
a  narrow  tube  3  to  4  inches  long  enlarged  below  to  a  small  bulb  to 
contain  the  carbonate.  This  bulb  must  be  so  thin  that  on  pushing 
down  the  tube  within  the  bottle  it  shall  be  easily  crushed  to  pieces 
against  the  bottom  of  the  latter.  The  carbonate  is  weighed  into 
the  bulb-tube,  the  latter  is  wiped  clean  down  to  the  bulb,  corked 
and  fixed  in  the  stopper.  The  apparatus  is  filled  as  before  with 
CO2  and  weighed.  Then  the  bulb  is  broken  and  the  process  fin- 
ished as  before  described.  In  three  estimations  on  sodium  carbo- 
nate, 4:1-54,  4:1-64,  and  41*58  percent,  of  CO3  were  obtained.  Cal- 
culation requires  41 '51  per  cent.] 

e.  All  Carbonates  without  exception  (Determination  by  absorp- 
tion and  weighing  of  CO2),  H.  ROSE. 

The  flask  for  decomposing  the  carbonate  should  be  small  (150 
c.c.),  in  order  to  facilitate  subsequent  removal  of  carbonic  acid  by 
aspiration,  unless  the  substance  froths  strongly  during  its  decom- 
position, in  which  case  a  larger  flask  must  be  used.  The  end  of 
the  funnel  tube,  after  it  is  inserted  in  the  rubber  stopper  which  is 
fitted  to  the  flask,  is  drawn  to  a  less  diameter  and  bent  upwards  in 
the  form  of  a  hook,  to  prevent  the  entrance  of  gas-bubbles.  Above 
the  stop-cock  its  internal  diameter  should  not  be  so  small  as  to  pre- 
vent water  when  poured  in  from  filling  it,  and  this  portion  should 
be  so  long  that  the  pressure  of  the  liquid  filling  it  will  suffice  to 
force  gas  through  the  apparatus.  A  piece  of  glass  tube  bent  at  a 
right  angle  is  fitted  to  the  funnel  by  means  of  a  piece  of  rubber 
tube  slipped  over  it. 

The  nearly  horizontal  glass  tube  (about  0*7  metre  long)  is  of 
thin  glass,  and  of  a  diameter  not  less  than  12  millimetres.  It  is 
inclined  to  such  extent  that  water  condensing  in  it  may  flow  back. 
The  upper  half  is  filled  with  granulated  dried  calcium  chloride, 
secured  in  place  by  a  little  cotton  or  asbestos  at  each  end.  In  the 
end  of  the  large  tube  a  small  tube  is  fitted  by  means  of  a  rubber 
stopper,  and  to  this  is  joined  by  a'  rubber  tube  the  potash  appara- 
tus and  soda-lime  tube  (weighable  either  jointly  or  separately) 
charged  with  absorbents,  as  described  §§  174,  175.  The  flask  is 
removed  to  receive  the  weighed  substance,  and  replaced  without 
disturbing  the  position  of  the  rest  of  the  apparatus.  It  can  now 
be  ascertained  whether  the  apparatus  will  leak  gas  by  forcing  a 
little  air  (free  from  carbonic  acid)  through  the  funnel  tube,  closing 


§  139.]  CARBONIC    ACID.  413 

the  stop-cock,  and  observing  whether  the  unequal  height  of  liquid 
in  the  two  limbs  of  the  potash  apparatus  remains  for  a  few  minutes. 
Introduce  a  little  water  through  the  funnel  tube,  and  next  acid 
slowly  by  turning  the  stop-cock  until  evolution  of  CO2  ceases. 
The  small  right-angled  tube,  to  which  is  attached  a  large  tube 
filled  with  fragments  of  potash  (see  §  175),  is  now  inserted  in 
the  glass  funnel,  and  a  slow  current  of  air  (1  bubble  per  second)  is 
drawn  through  the  apparatus  by  means  of  an  aspirator  (fig.  62) 
connected  with  the  soda-lime  tube.  The  aspirator  should  not  be 
connected  directly  to  the  soda-lime  tube,  but  to  a  calcium-chloride 
tube,  which  ought  to  be  connected  with  the  latter  during  the 
whole  operation.  As  soon  as  the  current  of  air  is  established, 


Fig.  60. 

apply  the  smallest  possible  flame  of  a  Bunsen  lamp,  best  main- 
tained constant  by  capping  the  burner  with  wire  gauze  until  the 
fluid  just  boils.  Keep  up  the  gentle  boiling  a  few  minutes  until 
water  condenses  in  the  tube,  but  not  until  condensed  drops  appear 
quite  up  to  the  calcium  chloride.  Remove  then  the  lamp,  and 
aspirate  a  while  longer  somewhat  faster.  The  volume  of  air  neces- 
sary to  remove  the  carbonic  acid  depends  upon  the  size  of  the 
decomposing  flask.  When  the  operation  is  completed,  disconnect 
the  absorbing  apparatus,  close  the  ends  with  caps  of  rubber  tubing, 
and  weigh  after  lapse  of  half  an  hour. 

For  liberating  the  carbonic  acid,  sulphuric  acid  (the  concen- 
trated diluted  with  4  or  5  times  its  volume  of  water)  is  best 


414 


DETERMINATION. 


[§  139. 


adapted,  provided  it  readily  decomposes  the  substance  without 
formation  of  insoluble  sulphates. 

"When  there  are  objections  to  using  sulphuric  acid,  dilute  hydro- 
chloric acid  (containing  about  10  per  cent)  may  be  used,  or  more 
rarely  nitric  acid.  Nitric  acid  cannot  be  used  when  substances  are 
present  which  cause  its  decomposition  ;  e.g.,  ferrous  salts  and  sul- 
phides. 

When  sulphuric  acid  is  used,  the  evolution  of  HaS  from  sul- 


Fig.  62. 

phides,  if  present,  may  be  prevented  by  adding  first  a  solution  of 
chromic  acid  or  mercuric  chloride.  If  sulphites  are  present,  use 
chromic  acid  or  potassium  chromate.  When  hydrochloric  acid  is 
employed,  the  disturbing  influence  of  compounds  which  cause  evo- 
lution of  chlorine  may  be  prevented  by  allowing  some  concentrated 
solution  of  stannous  chloride  to  run  into  the  flask  before  addition 
of  the  acid.  When  hydrochloric  acid  is  used,  or  even  sulphuric  in 
the  presence  of  chlorides,  it  is  best  to  guard  against  the  possibility 
of  carrying  HC1  gas  into  the  potash  apparatus  by  substituting 
STOLBA'S  preparation  of  anhydrous  copper  sulphate  and  pumice- 


§  139.]  CARBONIC    ACID.  415 

stone  (see  page  410)  for  that  portion  of  the  calcium  chloride  which 
fills  10-15  cm.  of  the  end  of  the  tube. 

A  modification*  of  the  above-described  apparatus,  possessing 
some  obvious  advantages,  is  shown  by  fig.  61.  In  place  of  the 
empty  part  of  the  long  glass  tube  shown  in  fig.  60  is  substituted  a 
smaller  strong  tube,  provided  with  a  cooling  apparatus  through 
which  water  circulates.  This  is  connected  by  a  piece  of  close- 
fitting  rubber  tube  with  the  remaining  part  d.  Some  suitable 
form  of  apparatus  for  absorbing  CO,  must,  of  course,  be  attached 
to  d  in  the  manner  shown  by  fig.  60.  The 
calcium-chloride  tube,  used  to  prevent  moist 
air  from  entering  the  absorbing  apparatus, 
is  conveniently  supported  by  attaching  it  to 
the  aspirator  (fig.  62).  The  aspirator  may 
be  connected  with  the  apparatus  from  the 
beginning  to  the  end  of  the  operation,  with 
its  stop-cock  so  adjusted  that  water  flows 
from  it  drop  by  drop.  In  conducting  the 
operation,  a  little  variation  from  the  before 
described  manipulation  is  admissible  on  ac- 
count of  the  presence  of  the  condensing  ap- 
paratus. After  enough  acid  has  been  ad- 
mitted to  effect  decomposition,  the  stop-cock 
of  a  is  closed,  a  little  liquid  still  being  al- 
lowed to  remain  above  it.  Heat  is  then 
applied  as  before  directed,  but  continued 
longer  until  the  CO2  is  almost  or  quite  ex- 
pelled from  the  flask  by  steam.  This  point 
7~  ~  is  indicated  by  almost,  or  nearly,  entire  ces- 

sation of  dropping  of  water  from  the  aspi- 
rator. Diminish  now  the  heat,  and  immediately  after  open  the 
stop-cock  of  a  and  let  air  (free  from  COa)  enter  and  replace  the 
condensing  steam.  Boil  again  to  expel  the  air  which  has  entered, 
after  which  a  small  volume  of  air  drawn  through  the  apparatus  by 
the  aspirator  will  ensure  the  bringing  of  all  the  CO,  into  the  absoib- 
ing  apparatus. 

f.  Estimation  ~by  Measuring  the  Gas. 

This  process  is  applicable  in  the  case  of  all  salts  which  are 


*  Devised  by  H.  L.  WELLS,  of  the  Sheffield  Laboratory. 


416 


DETERMINATION. 


[§  139. 


TABLE  OF  THE  WEIGHT  OF  A  CUBIC 

In  Milligrammes,  from  720  to  770  mm.  ofpress- 

MlLLIMETRES. 


720 

722 

724 

726 

728 

730 

732 

734 

736 

738 

740 

742 

744 

IQo  1.77446 

! 
1.77945'1.78445 

1.78944 

1.79443 

1.79942 

1.80441 

1.80941 

1.81440 

1.81940 

1.82438 

1.82937 

1.83437 

11* 

1.76668  1.77165  1.77662 

1.78160 

1.78657 

1.79155 

1.79652 

1.80149 

1.80647 

1.81144 

1.81642 

1.82139 

1.82636 

12°  1.75881 

1.76377 

1.76873 

1.77368 

1.77864 

1.78359 

1.78855 

1.79351 

1.79846 

1.80342 

1.80838 

1.81333 

1.81829 

13° 

1.75092 

1.75587 

1.76081 

1.76576 

1.77070 

1.77565 

1.78059 

1.78554 

1.79048 

1.79543 

1.80037 

1.80532 

1.81026 

14°;  1.74301 

1.74795 

1.75288 

1.75781 

1.76275 

1.76768 

1.77261 

1.77754 

1.78248 

1.78741 

1.79234 

1.79728 

1.80221 

150  1  1.73502 

1.73993 

1.74484 

1.74974 

1.75465 

1.75955 

1.76446 

1.76937 

1.77427 

1.77918 

1.78408 

1.78899 

1.79390 

16°  1.72699 

1.73188 

1.73677 

1.74166 

1.74655 

1.75144 

1.75633 

1.76122 

1.76611 

1.77100 

1.77590 

1.78078 

1.78567 

17°  1.71888 

1.72376 

1.72862 

1.73349 

1.73836 

1.74322 

1.74809 

1.75296 

1.75783 

1.76269 

1.76756 

1.77243 

1.77729 

18°  1.71069 

1.71554 

1.72040 

1.72525 

1.73011 

1.73497 

1.73982 

1.74468 

1.74953 

1.75439 

1.75925 

1.76410 

1.76896 

j 

19°  1.70239 

1.70723 

1.71207 

1.71691 

1.72175 

1.72659 

1.73143 

1.73627 

1.74111 

1.74595 

1.75078 

1.75562 

1.76046 

20°  1.69412 

1.69894 

1.70377 

1.70859 

1.71341 

1.71823 

1.72305 

1.72788 

1.73270 

1.73725 

1.74234 

1.74716 

1.75199 

21° 

1.68571  11.69051 

1.69532 

1.70012 

1.70493 

1.70974 

1.71454 

1.71935 

1.72415 

1.72896 

1.73377 

1.73857 

1.74338 

22° 

1.67722  1.68201  jl.68680 

1.69151 

1.69638 

1.70117 

1.70596 

1.71075 

1.71554 

1.72033 

1.72512 

1.72991 

1.73470 

23° 

1.66862  1.67340 

1.67817 

1.68294 

1.68772 

1.69249 

1.69727 

1.70204 

1.70681 

1.71159 

1.71636 

1.72114 

1.72591 

24° 

1.65994,1.66470 

1.66945 

1.67421 

1.67897 

1.68372 

1.68848 

1.69324 

1.69799 

1.70275 

1.70751 

1.71227 

1.71702 

25° 

1.65113  1.65587I1.66081 

1.66535 

1.67009 

1.67484 

1.67958 

1.68432 

1.68906 

1.69380 

1.69854 

1.70329 

1.70803 

720 

722 

724 

726 

728 

730 

732 

734 

736 

738 

740 

742 

744 

MILLIMETRES. 


§  139.] 


CAEBONIC   ACID. 


417 


CENTIMETRE  OF  CARBONIC  ACID. 

ure  of  mercury,  and  from  10°  to  25°  Cent. 

MILLIMETRES. 


746 

748'     750 

752 

754 

756  !  758 

760 

762 

764 

766 

768 

770 

i 

1 

i 

j 

i 

1.83936 

1.84435 

1.84934  1.85433 

1.85933  1.86432 

1.86931  1.87430 

1.87930 

1.884291.88928 

1.894271.89926 

10° 

. 

1.831341.83631 

1.84129  1.84626 

1.85123  1.85621 

1.86118 

1.86616 

1.87113  1.87610 

1.88108 

1.886051.89103 

11° 

1.82324 

1.82820 

1.833151.83811 

1.84307 

1.84802 

1.85298 

1.85793 

1.86289 

1.86785 

1.87280 

1.87776 

1.88271 

12° 

1.81521 

1.82015 

1.825101.83004 

1.83499 

1.83993 

1.84488  1.84982 

1.85477 

1.85971 

1.86466 

1.86960  1.87455 

13° 

1.80714 

1.81208 

1.81701 

1.82194 

1.82687 

1.83181 

1.83674 

1.84167 

1.84661 

1.85154 

1.85647 

1.86141 

1.86634 

14° 

1.79880 

1.80371 

1.80861 

1.81352 

1.81843 

1.82333 

1.82824 

1.83314 

1.83805 

1.84296 

1.84786 

1.852771.85767    15° 

1.79056 

1.79545 

1.800341.80523 

1.81012 

1.81501 

1.81990 

1.82479 

1.82968 

1.83457 

1.83946 

1.84435 

1.84924 

16° 

1.78216 

1.78703 

1.79189  1.79676 

1.80163 

1.80650 

1.81136 

1.81623 

1.82110 

1.82596 

1.83083 

1.83570  1.&4056    170 

1.77381 

1.77867 

1.783531.78838 

1.79324 

1.79809 

1.80295 

1.80781 

1.81266 

1.81752 

1.82337 

1.827231.83209    18o 

1.76530 

1.77014 

1.77498  1.77982 

1.78466 

1.78950 

1.79434 

1.79917 

1.80401 

1.80885 

1.81369 

1.81853  1.82337 

19° 

1.75681 

1.76113 

1.766451.77127 

1.77610 

1.78092 

1.78574 

1.79056 

1.79538 

1.80021 

1.80503 

1.809851.81467 

20° 

1.74818 

I 
1.75299  1.75780  1.76260 

1.76741 

1.77221 

1.77702 

1.78183 

1.78663 

1.79144 

1.79624 

1.80105  1.80586 

21° 

1.73949 

1.74428 

1.74907 

1.75386 

1.75865 

1.76344 

1.76823 

1.77302 

1.77781 

1.78260 

1.78739 

1.79218 

1.79697 

ft- 

1.73068 

1.73546 

1.74023 

1.74501 

1.74978 

1.75455 

1.75933 

1.76410 

1.76888 

1.77365 

1.77842 

1.78320 

1.78797 

23° 

1.72178 

1.72654 

1.73129 

1.73605 

1.74081 

1.74556 

1.75032 

1.75508 

1.75984 

1.76459 

1.76935 

1.77411 

1.77886 

24° 

1.71277 

1.71751 

1.72225  1.72699 

1.73173 

1.73648 

1.74122 

1.74596 

1.75070 

1.75544 

1.76018 

1.76492 

1.76967 

25° 

746 

748 

750 

752 

754 

756 

758 

760 

762 

764 

766 

768 

770 

MILLIMETRES. 


418 


DETERMINATION. 


[§  139. 


8  5 

8  S 

8  $ 

10 

§  * 

10 

1  s 

•JU 

CO   ^ 

id 

8  S 

10 

OS    j^. 

10' 

8  1 

00   22 

T-H       ^^ 

•*' 

8  1 

00   i$ 

id 

00   £ 

10' 

8  § 

CO 

s  w. 

*  2 

•^f 
id 

E  e 

10 

£  o 

co" 

CO    *~ 

*"  3 

8  3 

co  £2 

10 
10 

J>   ^ 

10 

$>« 

1O 

S  o 

8  3 

s  <a 

10 

OS 

£  » 

10 

8  S 

s  % 

CO* 

^ 
03   id 

o 
id 

oo 
*>   «o 

1O 

CD 

OS 

id 

8  5 

8  3 

00 

CO   03 

10   10* 

S  -8 

10' 

s  2 

s  s 

CO 

8  3 

«»   ^ 

S   OT 

id 

g  § 

10' 

/v»   CO 

8  5 

CO 

c3  s 

id 

s  s 

10   id 

3  i 

1^    O5 

id 

s  a. 

CO 

8  1 

g   1 

8  1 

OS    °? 

«  8- 

co' 

8  1 

2  w 
id 

8  3 

8  1 

00   "3s. 

CO 

c5   ° 

10 

S8  8. 

10 

8  1 

8  S 

00 

a  3 

s  s 

id 

S  8 

10 

CO 

00   °° 
10 

CO   § 
OJ 

8'  1 

«  8. 

10 

g  S 

10 

CO    ^ 

id 

10   ^ 

8  1 

$   8 

id 

JO   |§ 

"°   id 

s  1 

TH 

S  § 

t- 

^J   CO, 

id 

50   id 

id 

CO 
CO   """J 

8  5 

id 

CO 
CO    *° 
10 

s  i 

<M   O 

CO   °   ' 

CO   *°   ' 

id 

50   id 

§2  8. 

10 

TH 

s  3 

-  3  1 

s  1 

55  I 

Evolved  
Absorbed  

Evolved  
Absorbed  

Evolved  
Absorbed  

Evolved  
Absorbed  

Evolved  
Absorbed  

§  140.]  SILICIC  ACID.  419 

decomposed  by  hydrochloric  acid  in  the  cold.  It  is  distinguished 
for  rapid  and  convenient  execution  and  very  satisfactory  results. 
[The  azotometer,  fig.  63,  is  employed,  and  the  details  of  the 
process  are  for  the  most  part  similar  to  those  followed  in  the 
estimation  of  ammonia  as  described  on  page  222.  The  weighed 
carbonate  is  put  in  the  bottle  a,  and  the  tube/"  is  charged  with  5 
c.c.  of  H.  Cl.,  sp.  gr.  1-125.  When  the  burette  is  adjusted  to  zero, 
the  acid  is  poured  at  once  upon  the  carbonate.  The  precautions  to 
be  observed  in  the  measurement  of  the  gas  are  as  detailed  on  page 
222.  It  is  not  needful  to  wait  so  long  for  the  gas  to  cool.  The 
necessary  corrections  are  applied  by  aid  of  the  tables  given  by 
Dietrich,  pages  416-418.  Their  use  is  perfectly  similar  to  that  of 
the  tables  given  on  pages  223-225.] 

§  140. 
2.  SILICIC  Aero. 

I.  DETERMINATION. 

The  direct  estimation  of  silicic  acid  is  almost  invariably  effected 
by  converting  the  soluble  modification  of  the  acid  into  the  insol- 
uble modification,  by  evaporating  and  completely  drying ;  the 
insoluble  modification  is  then,  after  removal  .of  all  foreign  matter, 
ignited  strongly  (over  the  bellows  blowpipe)  and  weighed. 

For  the  guidance  of  the  student  I  would  observe  here  that,  to 
guard  against  mistakes,  he  should  always  test  the  purity  of  the 
weighed  silicic  acid.  The  methods  of  testing  will  be  found 
below. 

If  you  have  free  silicic  acid  in  the  state  of  hydrate,  in  an  aque- 
ous or  acid  solution  free  from  other  fixed  bodies,  simply  evaporate 
the  solution  in  a  platinum  dish,  ignite  and  weigh  the  residue. 

Respecting  a  volumetric  estimation  of  silicic  acid  (conversion 
into  potassium  silicofluoride  and  acidimetric  determination  of  the 
same,  see  §  97,  4),  I  must  refer  to  STOLBA.* 

II.  SEPARATION  OF  SILICIC  ACID  FROM  THE  BASIC  RAD- 
ICALS. 

a.  In  all  compounds  which  are  decomposed  T>y  Hydrochloric 
or  Nitric  Acid,  on  digestion  in  open  vessels. 


*  Zcitschr.  f.  anal.  Chem.  4,  163. 


420  DETERMINATION.  [§  140. 

To  this  class  belong  the  silicates  soluble  in  water,  as  well  as 
many  of  the  insoluble  silicates,  as,  for  instance,  nearly  all  zeolites. 
Several  minerals  not  decomposable  of  themselves  by  acids,  become 
so  by  persistent  ignition  in  a  state  of  fine  powder  (F.  MOHK*).  If 
the  ignition  is  too  strong,  particles  of  alkali  may  be  lost. 

The  substance  is  very  finely  powdered, f  dried  at  1 00°,  and  put 
into  a  platinum  or  porcelain  dish  (in  the  case  of  silicates  whose  solu- 
tion might  be  attended  with  disengagement  of  chlorine,  platinum 
cannot  be  used) ;  a  little  water  is  then  added,  and  the  powder 
mixed  to  a  uniform  paste.  Moderately  concentrated  hydrochloric 
acid,  or — if  the  substance  contains  lead  or  silver — nitric  acid,  is  now 
added,  and  the  mixture  digested  at  a  very  gentle  heat,  with  con- 
stant stirring,  until  the  substance  is  completely  decomposed,  in 
other  terms,  until  the  glass  rod,  which  is  rounded  at  the  end, 
encounters  no  more  gritty  powder,  and  the  stirring  proceeds 
smoothly  without  the  least  grating. 

The  silicates  of  this  class  do  not  all  comport  themselves  in  the 
same  manner  in  this  process,  but  show  some  differences ;  thus  most 
of  them  form  a  bulky  gelatinous  mass,  whilst  in  the  case  of  others 
the  silicic  acid  separates  as  a  light  pulverulent  precipitate ;  again, 
many  of  them  are  decomposed  readily  and  rapidly,  whilst  others 
require  protracted  digestion. 

When  the  decomposition  is  effected,  the  mixture  is  evaporated 
to  dryness  on  the  water-bath,  and  the  residue  heated,  with  frequent 
stirring,  until  all  the  small  lumps  have  crumbled  to  pieces,  and  the 
whole  mass  is  thoroughly  dry,  and  until  no  more  acid  fumes  escape. 
It  is  always  the  safest  way  to  conduct  the  drying  on  the  water-bath. 
Occasionally  it  is  well  to  moisten  the  dry  mass  with  water  and  evap- 
orate again.  In  cases  where  it  appears  desirable  to  accelerate  the 
desiccation  by  the  application  of  a  stronger  heat,  an  air-bath  may 
be  had  recourse  to ;  which  may  be  constructed  in  a  simple  way,  by 
suspending  the  dish  containing  the  substance,  with  the  aid  of  wire, 
in  a  somewhat  larger  dish  of  silver  or  iron,  in  a  manner  to  leave 
everywhere  between  the  two  dishes  a  small  space  of  uniform  width. 
Direct  heating  over  the  lamp  is  not  advisable,  as  in  the  most 
strongly  heated  parts  the  silicic  acid  is  liable  to  unite  again  with 

*  Zeitschr.  f.  anal.  Chem.  7,  293. 

t  Very  hard  silicates  cannot  be  powdered  in  an  agate  mortar  without  taking 
up  silica;  these  must,  therefore,  be  powdered  in  a  steel  mortar,  sifted,  and  freed 
from  particles  of  steel  with  the  magnet. 


§  140.]  SILICIC  ACID.  421 

the  separated  bases  to  compounds  which  are  not  decomposed,  or 
only  imperfectly,  by  hydrochloric  acid. 

When  the  mass  is  cold,  it  is  brought  to  a  state  of  semi-fluidity 
by  thoroughly  moistening  it  with  hydrochloric  acid  ;  after  which 
it  is  allowed  to  stand  for  half  an  hour,  then  warmed  on  a  water- 
bath,  diluted  with  hot  water,  stirred,  allowed  to  deposit,  and  the 
fluid  decanted  on  to  a  filter ;  the  residuary  silicic  acid  is  again 
stirred  with  hydrochloric  acid,  warmed,  diluted,  and  the  fluid  once 
more  decanted  ;  after  a  third  repetition  of  the  same  operation,  the 
precipitate  also  is  transferred  to  the  filter,  thoroughly  washed  with 
hot  water,  well  dried,  and  ignited  at  last  as  strongly  as  possible,  as 
directed  in  §  52.  For  the  properties  of  the  residue,  see  §  93,  9. 
The  results  are  accurate.  The  basic  metals,  which  are  in  the  filtrate 
as  chlorides,  are  determined  by  the  methods  given  above.  Devia- 
tions from  the  instructions  here  given  are  likely  to  entail  loss  of 
substance  ;  thus,  for  instance,  if  the  mass  is  not  thoroughly  dried, 
a  not  inconsiderable  portion  of  the  silicic  acid  passes  into  the  solu- 
tion, whereas,  if  the  instructions  are  strictly  complied  with,  only 
traces  of  the  acid  are  dissolved  ;  in  accurate  analyses,  however,  even 
such  minute  traces  must  not  be  neglected,  but  should  be  separated 
from  the  metals  precipitated  from  the  solution.  The  separation 
may,  as  a  rule,  be  readily  effected  by  dissolving  them,  after  ignition 
and  weighing,  in  hydrochloric  or  sulphuric  acid,  by  long  digestion 
in  the  heat,  the  traces  of  silicic  acid  being  left  undissolved.  Some- 
times it  is  better  to  fuse  the  metallic  oxides  with  potassium  disul- 
phate,  or  to  reduce  them  to  the  metallic  state  by  ignition  in  hydro- 
gen, and  then  to  treat  with  hydrochloric  acid.  Again,  if  the  silicic 
acid  is  not  thoroughly  dried  previous  to  ignition,  the  aqueous  vapor 
disengaged  upon  the  rapid  application  of  a  strong  heat  may  carry 
away  particles  of  the  light  and  loose  silica. 

The  silicic  acid  may  be  tested  as  follows :  This  testing  must  on 
no  account  be  omitted  if  the  silica  has  been  separated  in  a  pulveru- 
lent and  not  in  a  gelatinous  form.  Heat  a  portion  on  a  water-bath 
with  moderately  concentrated  solution  of  sodium  carbonate  for  an 
hour  in  a  platinum  or  silver  dish  ;  with  less  advantage  in  a  porce- 
lain dish.  EGGERTZ"*  recommends,  for  •  1  grm.  silicic  acid,  6  c.c. 
of  a  saturated  solution  of  sodium  carbonate  and  12  c.c.  of  water. 
Pure  silica  would  dissolve.  If  a  residue  remains,  pour  off  the  clear 

*  Zeitschr.  f .  anal.  Chem.  7,  502. 


422  DETERMINATION.  [§  140. 

fluid  and  heat  again  with  a  small  quantity  of  sodium  carbonate.  If 
a  residue  still  remains,  weigh  the  rest  of  the  impure  silica  and 
treat  it  according  to  &,  to  estimate  the  amount  of  impurity. 

If  you  have  pure  hydrofluoric  acid,  you  may  also  test  the  silicic 
acid  in  a  very  easy  manner,  by  treating  it  with  this  acid  and  a  few 
drops  of  sulphuric  acid  in  a  platinum  dish  ;  upon  the  evaporation 
of  the  solution,  the  silicic  acid,  if  pure,  will  volatilize  completely 
(as  fluoride  of  silicon).  If  a  residue  remains,  moisten  this  once 
more  with  hydrofluoric  acid,  add  a  few  drops  of  sulphuric  acid, 
evaporate,  arid  ignite  ;  the  residue  consists  of  the  sulphates  of  the 
metals  retained  by  the  silicic  acid,  as  well  as  any  titanic  acid  that 
was  present  (BEKZELIUS).  Ammonium  fluoride  may  be  used 
instead  of  hydrofluoric  acid. 

b.  Compounds  which  are  not  decomposed  "by  Hydrochloric  or 
Nitric  Acid,  on  digestion  in  open  vessels. 

a.  Decomposition  by  fusion  with  Alkali  Carbonate. 

Reduce  the  substance  to  an  impalpable  powder,  by  triturat'ion 
and,  if  necessary,  sifting  (§  25) ;  transfer  to  a  platinum  crucible, 
and  mix  with  about  4  times  the  weight  of  pure  anhydrous  sodium 
carbonate  or  sodium  and  potassium  carbonate,  with  the  aid  of  a 
rounded  glass  rod ;  wipe  the  rod  against  a  small  portion  of  sodium 
carbonate  on  a  card,  and  transfer  this  also  from  the  card  to  the 
crucible.  Cover  the  latter  well,  and  heat,  according  to  size,  over  a 
gas  or  spirit-lamp  with  double  draught,  or  a  blast  gas-lamp  ;  or 
insert  in  a  Hessian  crucible,  compactly  filled  up  writh  calcined 
magnesia,  and  heat  in  a  charcoal  fire. 

Apply  at  first  a  moderate  heat  for  some  time  to  make  the  mass 
simply  agglutinate ;  the  carbonic  acid  will,  in  that  case,  escape  from 
the  porous  mass  with  ease  and  unattended  with  spirting.  Increase 
the  heat  afterwards,  finally  to  a  very  high  degree,  and  terminate 
the  operation  only  when  the  mass  appears  in  a  state  of  calm  fusion, 
and  gives  no  more  bubbles. 

The  platinum  crucible  in  which  the  fusion  is  conducted  must 
not  be  too  small ;  in  fact,  the  mixture  should  only  half  fill  it.  The 
larger  the  crucible,  the  less  risk  of  loss  of  substance.  As  it  is  of 
importance  to  watch  the  progress  of  the  operation,  the  lid  must  be 
easily  removable  ;  a  concave  cover,  simply  lying  on  the  top,  is  there- 
fore preferable  to  an  overlapping  lid.  If  the  process  is  conducted 
over  the  spirit  or  simple  gas-lamp,  the  mixed  sodium  and  potas- 


§  140.J  SILICIC   ACID.  423 

siurn  carbonates  are  preferable  to  sodium  carbonate,  as  they  fuse 
much  more  readily  than  the  latter.  In  heating  over  a  lamp,  the 
crucible  should  always  be  supported  on  a  triangle  of  platinum  wire, 
with  the  opening  just  sufficiently  wide  to  allow  the  crucible  to 
drop  into  it  fully  one  third,  yet  to  retain  it  firmly,  even  with  the 
wire  at  an  intense  red  heat.  When  conducting  the  process  over  a 
spirit-lamp  with  double  draught,  or  over  a  simple  gas-lamp,  it  is 
also  advisable,  towards  the  end  of  the  operation,  when  the  heat  is 
to  be  raised  to  the  highest  degree,  to  put  a  chimney  over  the  cruci- 
ble, with  the  lower  border  resting  on  the  ends  of  the  iron  triangle 
which  supports  the  platinum  triangle ;  this  chimney  should  be 
about  12  or  14  cm.  high,  and  the  upper  opening  measure  about  4 
cm.  in  diameter.  The  little  clay  chimneys  recommended  by  O.  L. 
ERDMAXX  are  still  more  serviceable  (fig.  21,  p.  24,  "  Qual.  Anal."). 
When  the  fusion  is  ended,  the  red-hot  crucible  is  removed  with 
tongs,  and  placed  on  a  cold,  thick,  clean  iron  plate,  on  which  it 
will  rapidly  COQ!  ;  it  is  then  generally  easy  to  detach  the  fused  cake 
in  one  piece. 

The  cake  (or  the  crucible  with  its  contents)  is  put  into  a  beaker, 
from  10  to  15  times  the  quantity  of  water  poured  over  it,  and  heat 
applied  for  half  an  hour,  then  hydrochloric  acid  is  gradually  added, 
or,  under  certain  circumstances,  nitric  acid;  the  beaker  is  kept 
covered  with  a  glass  plate,  or,  which  is  much  better,  with  a  large 
watch-glass  or  porcelain  dish,  perfectly  clean  outside,  to  prevent 
the  loss  of  the  drops  of  fluid  which  the  escaping  carbonic  acid  car- 
ries along  with  it ;  the  drops  thus  intercepted  by  the  cover  are 
afterwards  rinsed  into  the  beaker.  The  crucible  is  also  rinsed  with 
water  mixed  with  dilute  acid,  and  the  solution  obtained  added  to 
the  fluid  in  the  beaker. 

The  solution  is  promoted  by  the  application  of  a  gentle  heat, 
which  is  continued  for  some  time  after  this  is  effected  to  insure  the 
complete  expulsion  of  the  carbonic  acid ;  since  otherwise  some  loss 
of  substance  might  be  incurred,  in  the  subsequent  process  of  evapo- 
ration, by  spirting  caused  by  the  escape  of  that  gas.  If  in  the  pro- 
cess of  treating  the  fused  mass  with  hydrochloric  acid,  a  saline 
powder  subsides  (sodium  or  potassium  chloride),  this  is  a  sign  that 
more  water  is  required. 

If  the  decomposition  of  the  mineral  has  succeeded  to  the  full 
extent,  the  hydrochloric  acid  solution  is  either  perfectly  clear,  or 
light  flakes  of  silicic  acid  only  float  in  it.  But  if  a  heavy  powder 


424  DETEKMHSTATION.  [§  140. 

subsides,  which  feels  gritty  under  the  glass  rod,  this  consists  of 
undecomposed  mineral.  The  cause  of  such  imperfect  decomposi- 
tion is  generally  to  be  ascribed  to  imperfect  pulverization.  In 
such  cases  the  undecomposed  portion  may  be  fused  once  more  with 
alkali  carbonate  ;  the  better  way,  however,  is  to  repeat  the  process 
with  a  fresh  portion  of  mineral  more  finely  pulverized. 

The  hydrochloric  or  nitric  acid  solution  obtained  is  poured, 
together  with  the  precipitate  of  silicic  acid,  which  is  usually  floating- 
in  it,  into  a  porcelain  or,  better,  into  a  platinum  dish,  and  treated 
as  directed  in  II.,  a.  That  the  fluid  may  not  be  too  much  diluted, 
the  beaker  should  be  rinsed  only  once,  or  not  at  all,  and  the  few 
remaining  drops  of  solution  dried  in  it ;  the  trifling  residue  thus 
obtained  is  treated  in  the  same  way  as  the  residue  left  in  the  evapo- 
rating basin.  This  is  the  method  most  commonly  employed  to 
effect  the  decomposition  of  silicates  that  are  undecomposable  by 
acids ;  that  it  cannot  be  used  to  determine  alkalies  in  silicates  is 
self-evident. 

§.  Decomposition  ly  means  of  Hydrofluoric  Acid. 

aa.  By  Aqueous  Hydrofluoric  Acid. 

The  silicate  should  be  finely  pulverized,  dried  at  100°  (in  some 
cases  ignition  is  advisable*).  It  is  mixed,  in  a  platinum  dish,  with 
rather  concentrated,  slightly  fuming  hydrofluoric  acid,  the  acid 
being  added  gradually,  and  the  mixture  stirred  with  a  thick  plati- 
num wire.  The  mixture,  which  has  the  consistence  of  a  thin  paste, 
is  digested  some  time  on  a  water-bath  at  a  gentle  heat,  and  pure 
concentrated  sulphuric  acid,  diluted  with  an  equal  quantity  of 
water,  is  then  added,  drop  by  drop,  in  more  than  sufficent  quantity 
to  convert  all  the  basic  metals  present  into  sulphates.  The  mixture 
is  now  evaporated  on  the  water-bath,  during  which  operation  sili- 
con fluoride  gas  and  hydrofluoric  acid  gas  are  continually  volatiliz- 
ing ;  then  it  is  finally  exposed  to  a  stronger  heat  at  some  height  above 
the  lamp,  until  the  excess  of  sulphuric  acid  is  almost  completely 
expelled.  The  mass,  when  cold,  is  thoroughly  moistened  with  con- 
centrated hydrochloric  acid,  and  allowed  to  stand  at  rest  for  one 
hour;  water  is  then  added,  and  a  gentle  heat  applied.  If  the 
decomposition  has  fully  succeeded,  the  whole  must  dissolve  to  a 
clear  fluid.  If  an  undissolved  residue  is  left,  the  mixture  is  heated 

*  Many  minerals  are  much  more  readily  decomposed  by  hydrofluoric  acid 
also,  if  they  are  previously  ignited  in  a  state  of  fine  division  (HERMANN,  RAM- 
MELSBERG,  FR.  HOUR,  Zeitschr.  f.  anal.  Chem.  7,  291). 


§  140.]  SILICIC  ACID.  425 

for  some  time  on  the  water-bath,  then  allowed  to  deposit,  the  clear 
supernatant  fluid  decanted  as  far  as  practicable,  the  residue  dried, 
and  then  treated  again  with  hydrofluoric  acid  and  sulphuric  acid, 
and,  lastly,  with  hydrochloric  acid,  which  will  now  effect  complete 
solution,  provided  the  analyzed  substance  was  very  finely  pulver- 
ized, and  free  from  barium,  strontium  (and  lead).  The  solution  is 
added  to  the  first.  The  basic  metals  in  the  solution  (which  con- 
tains them  as  sulphates,  and  contains  also  free  hydrochloric  acid) 
are  determined  by  the  methods  which  will  be  found  in  Section  Y. 

This  method,  which  is  certainly  one  of  the  best  to  effect  the 
decomposition  of  silicates,  was  proposed  by  BERZELIUS.  It  has 
been  but  little  used  hitherto,  because  we  did  not  know  how  to  pre- 
pare hydrofluoric  acid,  except  with  the  aid  of  a  distilling  appa- 
ratus of  platinum,  or,  at  least,  with  a  platinum  head  ;  nor  to  keep 
it,  except  in  platinum  vessels.  These  difficulties  can  now  be  con- 
sidered as  overcome,  comp.  §  58,  2.  Never  omit  testing  the  acid 
before  using  it. 

The  hydrofluoric  acid  may  also  be  employed  in  combination 
with  hydrochloric  acid ;  thus  1  grm.  of  finely  elutriated  felspar, 
mixed  with  40  c.c.  water,  7  c.c.  hydrochloric  acid  of  25^  and  3J  c.c. 
hydrofluoric  acid,  and  heated  to  near  the  boiling  point,  dissolves 
completely  in  three  minutes.  4  c.c.  sulphuric  acid  are  then  added, 
the  barium  sulphate  which  may  separate  is  filtered  off,  and  the 
filtrate  evaporated  till  no  more  hydrofluoric  acid  escapes  (AL. 

MlTSCHERLICH*). 

The  execution  of  the  method  requires  the  greatest  possible  care, 
both  the  liquid  and  the  gaseous  hydrofluoric  acid  being  most 
injurious  substances.  The  treatment  of  the  silicate  with  the  acid 
and  the  evaporation  must  be  conducted  in  the  open  air,  otherwise 
the  windows  and  all  glass  apparatus  will  be  attacked.  As  the  silicic 
acid  is  in  this  method  simply  inferred  from  the  loss,+  a  combination 
with  method  a  is  often  resorted  to. 

bb.  By  Ammonium  Fluoride. 

Mix  the  very  finely  powdered  substance  in  a  platinum  dish 
with  four  times  its  weight  of  ammonium  fluoride,  moisten  well 
with  concentrated  sulphuric  acid,  heat  on  the  water-bath  till  the 

*  Journ.  f.  prakt.  Chem.  81,  108. 

f  The  silicon  escaping  in  the  form  of  fluoride  may  sometimes  be  determined 
directly,  by  the  method  of  STORY  MASKELYNE  (Zeitschr.  f.  anal.  Chem.  9,  380), 
which,  however,  requires  a  platinum  retort  of  peculiar  construction. 


426  DETERMINATION.  [§  140. 

•evolution  of  silicon  fluoride  and  hydrofluoric  acid  slackens,  add 
more  sulphuric  acid,  heat  again,  finally  somewhat  more  strongly 
till  the  greater  part  of  the  sulphuric  acid  has  escaped,  and  treat  the 
residue  according  to  aa  (L.  v.  BABO,  J.  POTYKA,  R.  HOFFMANN*). 
H.  Kosfif  first  warms  the  silicate  gently  with  seven  times  its 
amount  of  the  fluoride  and  some  water,  then  heats  gradually  to 
redness  till  no  more  fumes  escape,  and  finally  treats  with  sulphuric 
.acid. 

cc.  By  Fluoride  of  Hydrogen  and  Potassium,  dec. 

In  silicates,  which  more  or  less  resist  the  action  of  hydrofluoric 
acid,  such  as  zircon  and  beryl,  the  basic  metals  with  the  exception 
of  the  alkalies  may  be  determined  by  fusing  with  fluoride  of 
hydrogen  and  potassium  (MARIGNAC,  GiBBsf),  or  by  mixing  with 
3  parts  of  sodium  fluoride,  adding  1 2  parts  of  potassium  disulphate 
to  the  crucible,  and  then  heating  at  first  very  gently,  afterwards 
more  strongly  till  the  mass  fuses  calmly.  The  residue  is  dissolved 
in  water  or  hydrochloric  acid  (CLAKKE§). 

\y.  .Decomposition  by  ignition  with  Calcium  Carbonate  and 
Ammonium  Chloride.  PROF.  J.  L.  SMITH'S  METHOD  for  separating 
alkalies. 

Mix  1  part  of  the  pulverized  silicate  with  1  part  of  dry  ammo- 
nium chloride,  by  gentle  trituration  in  a  smooth  mortar,  then  add 
S  parts  of  calcium  carbonate  ("  Qual.  Anal."  p.  87)  and  mix  inti- 
mately. Bring  the  mixture  into  a  platinum  crucible,  rinsing  the 
mortar  with  a  little  calcium  carbonate.  Warm  the  crucible  gradu- 
ally over  a  small  Bunsen  burner  until  fumes  of  ammonium  salts  no 
longer  appear,  then  heat  with  the  flame  of  a  Bunsen  burner  until 
the  lower  three-fourths  only  of  the  crucible  are  brought  to  a  red 
heat.  Keep  this  temperature  constant  from  40  to  60  minutes. 
The  temperature  desired  is  that  which  suffices  to  keep  in  state  of 
fusion  the  calcium  chloride  formed  by  the  reaction  of  ammonium 
chloride  with  calcium  carbonate.  The  mass,  however,  does  not 
become  liquid  since  the  fused  calcium  chloride  is  absorbed  by  the 
large  quantity  of  calcium  carbonate  present.  If  the  silicate  is 
fused  by  application  of  too  strong  heat,  disintegration  of  the  mass 
at  the  end  of  the  operation  with  water  cannot  be  effected.  More- 
over, too  high  a  temperature  causes  volatilization  of  alkali  chlo- 

*  Zeitschr.  f .  anal.  Chem.  6,  366.  f  Pogg.  Annal.  108,  20. 

J  Zeitschr.  f.  anal.  Chem.  3,  399.  §  Ib.  7,  463. 


§  140.]  SILICIC  ACID.  427 

rides.  Certain  silicates — e.g.,  those  which  contain  much  ferrous 
iron — may  fuse  when  heated  with  the  above  mixture,  even  if  no 
higher  temperature  is  employed  than  is  necessary  to  effect  decom- 
position. If  this  occurs,  it  is  better  to  repeat  the  ignition  with  a 
new  portion  of  the  silicate,  using  8  to  10  parts  of  calcium  carbo- 
nate. The  mass  contracts  in  volume  during  the  ignition,  and  is 
usually  easily  detached  from  the  crucible.  Boil  it  in  a  covered 
porcelain  dish,  with  50-75  c.c.  water,  half  an  hour,  replacing  water 
lost  by  evaporation.  Decant  the  solution  from  the  residue  upon  a 
filter,  boil  the  residue  a  few  minutes  with  water,  and  decant  again. 
If  the  residue  is  now  all  in  a  finely  disintegrated  state,  it  may  be 
brought  upon  the  filter  and  washed.  But  if,  as  is  often  the  case,  a 
portion  remains  coherent  or  in  a  coarsely  granular  state,  it  must  be 
reduced  to  a  fine  state  of  division  by  trituration  with  a  porcelain 
or  agate  pestle  in  the  dish,  and  boiling  with  water  again.  By  a 
few  repetitions  of  the  trituration,  boiling  and  decanting,  allowing 
the  fine  suspended  portion  to  pass  upon  the  filter  each  time,  the 
whole  can  usually  be  transferred  to  the  filter  in  properly  disinte- 
grated condition  in  course  of  an  hour.  Xext  wash  until  a  few  drops 
of  the  washings  acidified  with  nitric  acid  give  but  a  slight  turbid- 
ity with  silver  nitrate.  The  filtrate  now  contains  the  alkalies  of 
the  silicate  as  chlorides  together  with  calcium  chloride  and  hydrox- 
ide. It  is  not  advisable  to  concentrate  this  filtrate  in  a  glass  vessel, 
since  it  might  take  an  appreciable  quantity  of  sodium  from  the 
glass.  Precipitate,  therefore,  the  calcium  at  once  with  ammonium 
carbonate  ;  allow  the  precipitate  to  settle,  and  concentrate  the 
supernatant  solution  in  a  porcelain  (or  platinum)  dish,  decanting  it 
into  the  latter,  portionwise  if  necessary,  rinsing  finally  the  precipi- 
tate into  the  porcelain  dish.  When  the  whole  is  thus  reduced  to 
about  30  c.c.,  add  a  little  more  ammonium  carbonate  and  ammonia, 
heat  and  filter  into  a  platinum  (or  porcelain)  dish,  evaporate  to 
dry  ness  on  a  water-bath,  expel  ammonium  chloride  by  ignition, 
dissolve  the  residual  alkali  chlorides  in  3  to  5  c.c.  of  water.  A 
little  black  or  dark-brown  flocculent  matter  usually  remains  undis- 
solved,  while  the  solution  may  still  contain  traces  of  calcium.  Add 
two  or  three  drops  of  ammonium  carbonate  and  ammonia,  warm 
gently,  and  filter  through  a  very  small  filter  -into  a  weighable  plati- 
num vessel.  Evaporate  to  dryness  on  a  water-bath,  heat  to  in- 
cipient fusion  of  the  alkali  chlorides,  and  after  cooling  weigh. 
Prof.  SMITH'S  method  is  the  most  convenient  of  all  methods 


428  DETERMINATION.  [§  141. 

for  extracting  alkalies  from  silicates,  and  is  universally  applicable, 
except  perhaps  in  presence  of  boric  acid.  When  carried  out  as 
here  described,  the  results  are  sufficiently  accurate  in  most  cases. 
If,  however,  the  silicate  is  rich  in  alkalies,  a  loss  amounting  to  0*1  or 
0*2  per  cent  of  the  mineral  is  possible.  If  great  accuracy  is  desired 
in  such  cases,  a  repetition  of  the  whole  process  may  be  applied  to 
the  residue  left  by  treatment  of  the  ignited  mass  with  water.  It- 
need  hardly  be  mentioned  that  unless  care  be  takei)  to  use  reagents 
perfectly  free  from  soda  and  to  avoid  action  of  solutions  on  glass, 
an  amount  of  soda  may  be  introduced  from  these  sources  equal  to 
0*1  or  0'2  per  cent  of  the  silicate.] 

Second  Group. 

CHLORINE  —  BROMINE—  IODINE  —  CYANOGEN  —  SFLPHUB. 


1.  CHLORINE. 

I.  Determination. 

Chlorine  may  be  determined  very  accurately  in  the  gravimetric 
as  well  as  in  the  volumetric  way.* 

a.  Gravimetric  Method.  —  Determination  as  Silver  Chloride. 

Solution  of  silver  nitrate,  mixed  with  some  nitric  acid,  is  added 
in  excess  to  the  solution  of  the  chloride,  the  precipitated  chloride 
is  made  to  unite  by  heating  and  agitating,  washed  by  decantation 
and  nitration,  dried,  and  ignited.  The  details  of  the  process  have 
been  given  in  §  115,  1,  a.  Care  must  be  taken  not  to  heat  the 
solution  mixed  with  nitric  acid,  before  the  nitrate  of  silver  has 
been  added  in  excess.  As  soon  as  the  latter  is  present  in  excess, 
the  silver  chloride  separates  immediately  and  completely  upon 
shaking  or  stirring,  and  the  supernatant  fluid  becomes  perfectly 
clear  after  standing  a  short  time  in  a  warm  place.  The  determina- 
tion of  chlorine  by  means  of  silver  is  therefore  more  readily  effected 
than  that  of  silver  by  means  of  hydrochloric  acid. 

1).  Volumetric  Methods. 

a.  By  Solution  of  Silver  Nitrate. 

In  §  115,  5,  we  have  seen  how  the  silver  in  a  fluid  may  be  esti- 
mated by  adding  a  standard  solution  of  sodium  chloride  until  no 


*  For  the  acidimetric  estimation  of  free  hydrochloric  acid,  see  §  192. 


§  141.]  CHLORINE.  429 

further  precipitation  ensues ;  in  the  same  way  we  may  determine 
also,  by  means  of  a  standard  solution  of  silver,  the  amount  of  hydro- 
chloric acid  in  a  fluid,  or  of  chlorine  in  combination  with  a  metal. 
PELOUZE  has  used  this  method  for  the  determination  of  several 
atomic  weights.  LEVOL*  proposed  a  modification  which  serves  to 
indicate  more  readily  the  exact  point  of  complete  precipitation. 
To  the  fluid,  which  must  be  neutral,  he  added  one  tenth  volume 
of  a  saturated  solution  of  sodium  phosphate.  When  the  whole  of 
the  chlorine  has  been  precipitated  by  the  silver,  the  further  addi- 
tion of  the  solution  of  silver  produces  a  yellow  precipitate  which 
does  not  disappear  upon  shaking  the  vessel.  FR.  MOHR  has  since 
replaced,  with  the  most  complete  success,  the  sodium  phosphate  by 
potassium  chromate. 

This  convenient  and  accurate  method  requires  a  perfectly  neu- 
tral solution  of  silver  nitrate  of  known  value.  The  strength  most 
convenient  is,  1  litre  =  1  at.  Cl.  I  recommend  the  following 
method  of  preparation :  Dissolve  18*80  to  18*85  grin,  pure  fused 
silver  nitrate  in  1100  c.c.  water,  and  filter  the  solution  if  required ; 
the  solution  is  purposely  made  too  strong  at  first.  Now  weigh  off 
exactly  four  portions  of  pure  sodium  chloride,  each  of  *10  to  *18 
grin.,  one  after  another.  The  salt  should  be  moderately  ignited, 
not  fused,  powdered  roughly  while  still  warm,  and  introduced  into 
a  small  dry  tube,  that  can  be  well  closed.  The  weighing  off  is  per- 
formed by  first  weighing  the  filled  tube,  then  shaking  out  into  a 
dry  beaker  the  quantity  required,  weighing  again,  dropping  a 
second  portion  into  beaker  No.  2,  weighing  again,  and  so  on. 
Each  portion  is  dissolved  in  20  to  30  c.c.  water,  and  about  3  drops 
of  a  cold  saturated  solution  of  pure  normal  potassium  chromate 
added. 

Fill  a  HOUR'S  burette  (in  very  accurate  analysis  an  ERDMANN'S 
float  should  be  used)  with  the  silver  solution,  and  run  it  slowly, 
with  constant  stirring,  into  the  light  yellow  solution  contained  in 
one  of  the  beakers.  Each  drop  produces,  where  it  falls,  a  red  spot, 
which  on  stirring  disappears,  o  \ving  to  the  instant  decomposition 
of  the  silver  chromate  with  the  sodium  chloride.  At  last,  how- 
ever, the  slight  red  coloration  remains.  Now  all  chlorine  has  com- 
bined with  silver,  and  a  little  silver  chromate  has  been  permanently 
formed.  Read  off  the  burette  and  reckon  how  much  silver  solu- 

*  Journ.  f.  prakt.  Chem.  60,  384. 


430  DETERMINATION.  [§  141. 

tion  would  have  been  required  for  -1  mol.  sodium  chloride,  i.e., 
5*85  grm.  Suppose  we  have  used  to  "110  sodium  chloride  18*7  c.c. 
silver  solution. 

•110 :  5-85  : :  18-7  :  x;  x  =  994-5. 

E~ow,  without  throwing  away  the  contents  of  the  first  beaker, 
make  a  second  and  third  experiment  in  the  same  manner,  of  course 
always  taking  notice  to  regard  the  same  shade  of  red  as  the  sign  of 
the  end.  The  results  of  these  are  reckoned  out  in  the  same  way 
as  the  first.  Suppose  they  gave  for  5'85  NaCl  995-0  and  993-0 
respectively,  we  take  the  mean  of  the  three  numbers,  which  is 
994*2,  and  we  now  know  that  we  have  only  to  take  this  number  of 
c.c.  of  silver  solution,  and  make  it  up  to  1000  c.c.  with  5*8  water, 
in  order  to  obtain  a  solution  of  the  required  strength,  i.e.,  1000  c.c. 
—  -1  mol.  JSTaCl.  But  if  994-2  requires  5-8  water,  1000  requires 
5*83.  Hence  we  fill  a  litre-flask  (previously  dried  or  rinsed  with 
a  small  portion  of  the  solution)  up  to  the  "  holding "  mark  with 
the  solution,  add  5*83  c.c.  water,  insert  a  caoutchouc  stopper,  and 
shake. 

The  solution  must  now  be  correct ;  however,  to  make  quite 
sure,  we  perform  another  experiment  with  it.  To  this  end  rinse 
the  empty  burette  with  the  new  solution,  fill  it  with  the  same  and 
test  with  the  portion  of  salt  in  beaker  No.  4.  The  c.c.  used  of 
silver  solution  must  now,  if  multiplied  by  -00585,  give  exactly  the 
weight  of  the  salt. 

Being  now  in  possession  of  a  standard  silver  solution,  and  being 
practised  in  exactly  hitting  the  transition  from  yellow  to  the  shade 
of  red,  we  are  in  the  position  to  determine  with  precision  chlorine 
in  the  form  of  hydrochloric  acid  or  of  a  metallic  chloride  soluble  in 
water.  The  fluid  to  be  tested  must  be  neutral — free  acids  dissolve 
the  silver  chromate.  The  solution  of  the  substance  is  therefore, 
if  necessary,  rendered  neutral  by  addition  of  nitric  acid  or  sodium 
carbonate  (it  should  be  rather  alkaline  than  acid),  about  3  drops 
of  the  solution  of  chromate  added,  and  then  silver  from  the  burette, 
till  the  reddish  coloration  is  just  perceptible.  The  number  of  c.c. 
used  has  only  to  be  multiplied  by  the  atomic  weight  of  chlorine 
or  the  mol.  weight  of  the  metallic  chloride  and  divided  by  10,000 
to  give  the  amount  of  these  respectively  present. 

If  the  operator  fears  he  has  added  too  much  silver  solution,  i.e., 
if  the  red  color  is  too  strongly  marked,  he  may  add  1  c.c.  of  a  solu- 


§  141.]  CHLORINE.  431 

tion  of  sodium  chloride  containing  5*85  in  a  litre  (and  therefore 
corresponding  to  the  silver  solution),  and  then  add  the  silver  drop 
by  drop  again.  Of  course  in  this  case  1  c.c.  must  be  deducted  from 
the  amount  of  silver  solution  used. 

The  results  are  very  satisfactory.  The  fluid  to  be  analyzed 
should  be  about  the  same  volume  as  the  solutions  employed  in 
standardizing  the  silver  solution,  and  also  about  the  same  strength, 
otherwise  the  small  quantity  of  silver  which  produces  the  colora- 
tion will  not  stand  in  the  same  proportion  to  the  chlorine  present. 
This  small  quantity  of  silver  solution  is  extremely  small,  varying 
between  -05  and  '1  c.c.:  the  inaccuracy  hereby  arising  even  in  the 
case  of  quantities  of  chlorine  differing  widely  from  that  originally 
used  in  standardizing  the  silver  solution  is  therefore  almost  incon- 
siderable. If  the  amount  of  silver  solution  necessary  to  impart  the 
coloration  always  remained  the  same,  we  should  have  simply  to 
deduct  the  amount  in  question  with  all  experiments,  in  order  to 
avoid  this  small  inaccuracy  entirely ,  since,  however,  the  greater 
the  quantity  of  silver  chloride  the  more  silver  chromate  is  required 
for  visible  coloration,  this  method  of  proceeding  would  not  increase 
the  exactness  of  the  results. 

ft.  By  Solution  of  Silver  Nitrate  and  Iodide  of  Starch 
(PisAisn's  method*). 

Add  to  the  solution  of  the  chloride,  acidified  with  nitric  acid,  a 
slight  excess  of  standard  solution  of  silver  nitrate,  warm,  and  filter. 
Determine  the  excess  of  silver  in  the  filtrate  by  means  of  solution 
of  iodide  of  starch  (see  p.  295),  and  deduct  this  from  the  amount 
of  silver  solution  used.  The  difference  shows  the  quantity  of  silver 
which  has  combined  with  the  chlorine;  calculate  from  this  the 
amount  of  the  latter.  Results  satisfactory. 

Of  these  volumetric  methods  of  estimating  chlorine,  the  first 
deserves  the  preference  in  all  ordinary  cases.  PISANI'S  method 
(5,  ft)  is  especially  suited  for  the  estimation  of  very  minute  quan- 
tities of  chlorine,  but  is  not  applicable  when— as  in  nitre  analyses- 
— large  quantities  of  alkaline  nitrate  are  present  (p.  290). 

II.  Separation  of  Chlorine  from  the  Metals, 
a.  In  Soluble  Chlorides. 

The  same  method  as  in  L,  a.  The  metals  in  the  filtrate  are 
separated  from  the  excess  of  the  salt  of  silver  by  the  methods 

*  Annal.  d.  Mines,  10,  83  ;  LTEBIG  and  KOPP'S  Jahresbericht,  1856,  751. 


432  DETERMINATION.  [§  141. 

which  will  be  found  in  Section  Y.  Chlorides  soluble  in  water  may 
also  be  completely  decomposed  by  cold  digestion  with  oxide  or 
carbonate  of  silver.  Silver  chloride  is  obtained,  while  the  metal 
combined  with  the  chlorine  is  converted  into  oxide  or  carbonate 
and  either  remains  in  solution  or  falls  down  with  the  silver  chlo- 
ride. Take  care  that  no  traces  of  oxide  or  carbonate  of  silver  pass 
into  the  filtrate. 

Stannous  chloride,  mercuric  chloride,  platinic  chloride,  the 
chlorides  of  antimony,  and  the  green  chloride  of  chromium,  form 
exceptions  from  the  rule. 

ex.  From  stannic  chloride,  silver  nitrate  would  precipitate, 
besides  silver  chloride,  a  compound  of  stannic  oxide  and  silver 
oxide.  To  precipitate  the  tin,  therefore,  the  solution  is  mixed  with 
concentrated  solution  of  ammonium  nitrate,  boiled,  allowed  to 
deposit,  decanted,  and  filtered  (compare  §  126,  1,  Z>),  and  the  chlo- 
rine in  the  filtrate  is  precipitated  with  solution  of  silver.  LOWEN- 
THAL,  the  inventor  of  this  method,  has  proved  its  accuracy.* 

ft.  When  mercuric  chloride  is  precipitated  with  solution  of 
silver  nitrate,  the  silver  chloride  thrown  down  contains  an  admix- 
ture of  mercury.  The  mercury  is,  therefore,  first  precipitated  by 
hydrogen  sulphide,  and  the  chlorine  in  the  filtrate  determined  as 
directed  in  §  169. 

y.  The  chlorides  of  antimony  are  also  decomposed  in  the  man- 
ner described  in  ft.  The  separation  of  basic  salt  upon  the  addi- 
tion of  water  may  be  avoided  by  addition  of  tartaric  acid.  The 
antimonious  sulphide  should  be  tested  for  chlorine. 

#.  Solution  of  silver  fails  to  precipitate  the  whole  of  the  chlo- 
rine from  solution  of  the  green  chloride  of  chromium  (PELIGOT). 
The  chromium  is,  therefore,  first  precipitated  with  ammonia,  the 
fluid  filtered,  and  the  chlorine  in  the  filtrate  precipitated  as  in  I.,  a. 

f.  From  platinic  chloride  silver  nitrate  throws  down  a  com- 
pound of  platinous  chloride  and  silver  chloride  (CoMAiLLEf).  We 
may  either  ignite  the  platinic  chloride  in  a  current  of  hydrogen 
and. pass  the  hydrochloric  acid  produced  into  solution  of  silver 
(BON&DOBFF)  ;  or  we  may  evaporate  the  solution  with  sodium  car- 
bonate, fuse  the  residue  in  a  platinum  crucible  and  determine  the 
chloride  in  the  aqueous  solution  of  the  fusion.  Or,  thirdly,  we 
may  (after  TOPSOE;};)  digest  the  moderately  dilute  solution  in  the 

*  Journ.  f.  prakt.  Cliem.  66,  371.  f  Zeitschr.  f.  anal.  Chem.  6,  121. 

t  Zeitschr.  f.  anal.  Chem.  9,  30. 


§  141.]  CHLORINE.  433 

cold  with  zinc  clippings  till  hydrogen  ceases  to  escape,  add  ammo- 
nia in  excess,  heat  on  a  water-bath  till  the  fluid  is  fully  decolorized, 
all  the  platinum  being  precipitated,  and  finally  determine  the  chlo- 
rine in  the  filtrate. 

b.  In  Insoluble  Chlorides. 

a.  Chlorides  soluble  in  Nitric  Acid. 

Dissolve  the  chloride  in  nitric  acid,  without  applying  heat,  and 
proceed  as  in  I.,  a. 

fi.    Chlorides  insoluble  in  Nitric  Acid  (lead  chloride, 
silver  chloride,  mercurous  chloride). 

aa.  Lead  chloride  is  decomposed  by  digestion  with  alkali 
hydrogen  carbonate  and  water.  The  process  is  exactly  the  same 
as  for  the  decomposition  of  lead  sulphate  (§  132,  II.,  b,  /?). 

bb.  Silver  chloride  is  ignited  in  a  porcelain  crucible,  with  3 
parts  of  sodium  and  potassium  carbonate,  until  the  mass  com- 
mences to  agglutinate.  Upon  treating  with  water,  the  metallic 
silver  is  left  undissolved ;  the  solution  contains  the  alkali  chloride, 
which  is  then  treated  as  in  I.,  a. 

Silver  chloride  may  also  be  readily  decomposed  by  long  diges- 
tion with  pure  iron  (reduced  by  hydrogen)  and  dilute  sulphuric 
acid.  Zinc  may  be  used  instead  of  iron,  but  it  does  not  answer  so 
well.  The  separated  metallic  silver  may  be  washed,  heated  with 
dilute  sulphuric  acid,  washed  again  and  weighed ;  it  must  after- 
wards be  ascertained,  however,  whether  it  dissolves  in  nitric  acid. 
The  chlorine  is  determined  in  the  chloride  of  iron  or  zinc  as  in 
I,  a, 

cc.  Mercurous  chloride  is  decomposed  by  digestion  with  solu- 
tion of  soda  or  potassa.  The  hydrochloric  acid  in  the  filtrate  is 
determined  as  in  I.,  a.  The  mercurous  oxide  is  dissolved  in  nitric 
or  nitrohydrochloric  acid,  and  the  mercury  determined  as  directed 
in  §  117  or  §  118. 

c.  The  soluble  chlorides  of  the  metals  of  the  fourth*  fifth,  and 
sixth  groups  may  generally  be  decomposed  also  by  hydrogen  sul- 
phide or  ammonium,  sulphide.     The   chlorine   in   the   filtrate  is 
determined  as  in  §  169.     It  must  not  be  omitted  to  test  the  pre- 
cipitated sulphides  for  chlorine.     Several  chlorides,  cadmium  chlo- 
ride for  instance,  give  sulphides  free  from  chlorine  with  ammonium 
sulphide,  but  not  with  hydrogen  sulphide. 

d.  In  many  metallic  chlorides,  for  instance  in  those  of  the  first 
and  second  groups,  the  chlorine  may  be  determined  also  by  evapo- 


434  DETERMINATION.  [§  142. 

rating  with  sulphuric  acid,  converting  the  metal  thus  into  a  sul- 
phate, which  is  then  ignited  and  weighed  as  such ;  the  chlorine 
being  calculated  from  the  loss.  This  method  is  not  applicable  in 
the  case  of  silver  chloride  and  lead  chloride,  which  are  only  imper- 
fectly and  with  difficulty  decomposed  by  sulphuric  acid ;  nor  in 
the  case  of  mercuric  chloride  and  stannic  chloride,  which  sulphuric 
acid  fails  almost  or  altogether  to  decompose. 

Supplement. 

§142. 
DETERMINATION  OF  CHLORINE  IN  THE  FREE  STATE. 

Chlorine  in  the  free  state  may  be  determined  both  in  the  volu- 
metric and  in  the  gravimetric  way.  The  volumetric  methods, 
however,  deserve  the  preference  in  most  cases.  They  are  very 
numerous. 

I  shall  only  here  adduce  that  one  which  is  undoubtedly  the 
most  accurate  and  at  the  same  time  the  most  convenient.* 

1.   Volumetric  Method. 
With  Potassium  Iodide  (after  BUNSEN). 

Bring  the  chlorine,  in  the  gaseous  form  or  in  aqueous  solution, 
into  contact  with  an  excess  of  solution  of  potassium  iodide  in  water. 
Each  at.  chlorine  liberates  1  at.  iodine,  which  remains  dissolved  in 
the  excess  of  potassium  iodide.  By  determining  the  liberated  iodine 
by  means  of  sodium  thiosulphate  as  in  §  146,  you  will  accordingly 
learn  the  quantity  of  chlorine,  and,  in  fact,  with  the  greatest  accuracy. 
If  you  have  to  determine  the  chlorine  of  chlorine  water,  measure 
a  portion  off  with  a  pipette.  So  as  to  prevent  any  of  the  gas 
entering  the  mouth,  connect  the  upper  end  of  the  pipette  with  a 
tube  containing  moist  hydrate  of  potassa  laid  between  cotton. 
When  the  pipette  has  been  correctly  filled  allow  its  contents  to  flow, 
with  stirring,  into  an  excess  of  solution  of  potassium  iodide  (1  in  10). 
There  is  no  difficulty  about  knowing  whether  the  latter  is  sufficiently 
in  excess,  for  if  not,  a  black  precipitate  is  formed.  If  the  chlorine 
is  evolved  in  the  gaseous  condition,  you  may  employ  either  the 
apparatus  given  in  §  130,  I.,  d,  /?,  or  the  following,  which  is 
especially  suitable  where  the  chlorine  is  not  pure,  but  is  mixed 
with  other  gases. 

*  Compare  "  Chlorimetry"  in  the  Special  Part. 


§  142.]  CHLORINE.  435 

a  is  a  little  flask,  from  which  the  chlorine  is  evolved  by  boiling 
the  substance  with  hydrochloric  acid,  a  small  lump  of  magnesite 
being  added  ;  it  is  connected  with  the  tube,  &,  by  means  of  a  flexible 
tube.  The  latter  must  be  free  from  sulphur — should  it  contain 
sulphur  it  is  well  boiled  with  dilute  potassa  and  then  thoroughly 
washed.  The  thinner  tube,  <?,  which  has  been  fused  to  the  bulb  of  J, 
leads  through  the  caoutchouc  stopper  (which  has  been  deprived  of  sul- 
phur) to  the  bulbed  TJ-tube,  d,  which  contains  solution  of  potassium 
iodide,  and  which  for  safety  is  connected  with  the  plain  U-tube,  0,  also 
containing  potassium  iodide  solution.  Both  tubes  stand  in  a  beaker 


Fig.  64. 

filled  with  water.  The  apparatus  offers  the  advantages  that  the 
fluid  cannot  return,  that  the  potassium  iodide  remains  cold,  and 
that  the  absorption  is  complete.  After  all  the  chlorine  has  been 
expelled  by  boiling  long  enough,  rinse  d  and  e  out  into  a  beaker  and 
titrate  with  standard  sodium  thiosulphate  (§  146). 

2.   Gravimetric  Method. 

The  fluid  under  examination,  which  must  be  free  from  sulphu- 
ric acid,  say,  for  instance,  30  grm.  chlorine  water,  is  mixed  in  a  stop- 
pered bottle,  with  a  slight  excess  of  sodium  thiosulphate,  say  •  5  grm., 
the  stopper  inserted,  and  the  bottle  kept  for  a  short  time  in  a 


436  DETERMINATION.  [§  143. 

warm  place;  after  wliicli  the  odor  of  chlorine  is  found  to  have 
gone  off.  The  mixture  is  then  heated  to  boiling  with  some  hydro- 
chloric acid  in  excess,  to  destroy  the  excess  of  sodium  thiosulphate, 
filtered,  and  the  sulphuric  acid  in  the  filtrate  determined  by  barium 
chloride  (§  132).  1  mol.  sulphuric  acid  corresponds  to  4  at.  chlorine 

(WlCKE*). 

In  fluids  containing,  besides  free  chlorine,  also  hydrochloric  acid, 
or  a  metallic  chloride,  the  chlorine  existing  in  a  state  of  combination 
may  be  determined,  in  presence  of  the  free  chlorine,  in  the  follow- 
ing way : 

A  weighed  portion  of  the  fluid  is  mixed  with  solution  of  sulphur- 
ous acid  in  excess,  after  some  time  nitric  acid  is  added,  and  then  potas- 
sium chromate  to  destroy  the  excess  of  sulphurous  acid,  and  the 
whole  of  the  chlorine  is  precipitated  as  silver  chloride.  The  quantity 
of  the  free  chlorine  is  then  determined  in  another  weighed  portion, 
by  means  of  potassium  iodide ;  the  difference  gives  the  amount  of 
combined  chlorine. f 


Having  thus  seen  in  how  simple  and  accurate  a  manner  the 
quantity  of  free  chlorine  may  be  determined  by  BTTNSEN'S  method, 
it  will  be  readily  understood  that  all  oxides  and  peroxides  which 
yield  chlorine  when  heated  with  hydrochloric  acid,  may  be  analyzed 
by  heating  them  with  concentrated  hydrochloric  acid,  with  addition 
of  a  small  lump  of  magnesite,  and  determining  the  amount  of 
chlorine  evolved. 


2.  BROMINE. 

I.  Determination. 
a.   Gravimetric  Methods. 

Estimation  as  silver  bromide.     Free  hydrobromic  acid  —  in  a 
solution  free  from  hydrochloric  acid  or  chlorides  —  is  precipitated 


*  Annal.  d,  Chem.  u.  Pharm.  99,  99. 

f  If  chlorine  water  is  mixed  at  once  with  silver  nitrate,  f  only  of  the  chlorine 
is  obtained  as  silver  chloride  :  601  +  3Ag2O  =  SAgCl  -+-  AgClO3  (H.  ROSE,  WELT- 
ZIEN,  Annal.  d.  Chem.  u.  Pharm.  91,  45).  If  chlorine  water  is  mixed  with 
ammonia  in  excess,  there  are  formed  at  first  ammonium  chloride  and  ammonium 
hypochlorite,  the  latter  then  gradually  decomposes  into  nitrogen  and  ammonium 
chloride  ;  however,  a  little  ammonium  chlorate  is  also  formed 
Journ.  f.  prakt.  Chem.  84,  386;  Zeitschrift  f.  analyt.  Chem.  2,  59). 


§  143.]  BROMINE.  437 

by  silver  solution,  and  the  further  process  is  conducted  as  in  the 
case  of  hydrochloric  acid  (g  141).  For  the  properties  of  silver  bro- 
mide, see  §  94,  2.  The  results  are  perfectly  accurate. 

b.  Volumetric  Methods. 

Like  chlorine  in  hydrochloric  acid  and  alkali  chlorides,  bromine 
may  be  estimated  in  the  analogous  compounds  by  standard  silver 
solution  (§  141, 1.,  &,  or),  by  solution  of  silver  and  iodide  of  starch 
(§  141,  I.,  &,  /?).  But  these  methods  are  seldom  applicable,  as  they 
cannot  be  used  in  the  presence  of  hydrochloric  acid  and  metallic 
chlorides. 

The  following  methods  must  therefore  be  detailed ;  they  are 
especially  useful  for  the  estimation  of  small  quantities  of  bromine 
in  solutions  containing  chlorides,  but  in  point  of  accuracy  they 
leave  much  to  be  desired.* 

a.  With  chlorine  water  and  chloroform  (after  A.  REiMANNf). 
This  method  depends  on  the  facts  that  chlorine  when  added  to 
bromides  first  liberates  the  bromine  and  then  combines  with  it,  and 
that  bromine  colors  chloroform  yellow  or  orange,  while  bromine 
chloride  merely  communicates  a  yellowish  tinge  to  that  fluid.  The 
process  is  as  follows :  Mix  the  liquid  containing  a  bromide  of  an 
alkali  nietal  in  neutral  solution,  in  a  stoppered  bottle  with  a  drop 
of  pure  chloroform  about  the  size  of  a  hazel-nut,  then  add  standard 
chlorine  water  from  a  burette,  protected  from  the  light  by  being 
surrounded  with  black  paper.  On  shaking,  the  chloroform  becomes 
yellow,  on  further  addition  of  chlorine  water,  orange,  then  yellow 
again,  and  lastly — at  the  moment  when  2  at.  chlorine  have  been 
used  for  1  at.  bromine — yellowish  white  (KBr  +  2C1  =  KC1  + 
BrCl).  Considerable  practice  and  skill  are  required  before  the 
operator  can  tell  the  end-reaction.  He  will  be  assisted  by  placing 
the  bottle  on  white  paper  and  comparing  the  color  of  the  chloro- 
form with  that  of  a  dilute  solution  of  yellow  potassium  chromate 
of  the  required  color.  The  strength  of  the  chlorine  water  should 
depend  on  the  amount  of  the  bromine  to  be  determined.  It  should 
be  so  adjusted  that  about  100  c.c.  may  be  used.  The  chlorine  water 
is  standardized  with  potassium  iodide  and  sodium  thiosulphate 
(§  142,  1).  The  method  is  especially  suited  for  the  determination 
of  small  quantities  of  bromine  in  mother  liquors,  kelp,  &c.  The 
results  are  approximate :  e.g.,  "0180  instead  of  -0185 — -055  instead 


Compare  §  169.  f  Annal.  d.  Chem.  u.  Pharm.  115,  140. 


438  DETERMINATION.  [§  143. 

of  -059 — -0112  instead  of  '0100,  &c.  If  the  fluid  contains  organic 
substances,  it  is — after  being  rendered  alkaline  with  caustic  soda — 
evaporated  to  dryness,  the  residue  ignited  in  a  silver  dish,  extracted 
with  water,  the  solution  neutralized  exactly  with  hydrochloric  acid, 
and  then  tested. 

/?.  HEINE'S  colorimetric  method*  The  bromine  is  liberated 
by  means  of  chlorine,  and  taken  up  with  ether;  the  solution  is 
compared,  with  respect  to  color,  with  an  ethereal  solution  of  bro- 
mine of  known  strength,  and  the  quantity  of  bromine,  in  it  thus 
ascertained.  TEHLING^  obtained  satisfactory  results  by  this  method. 
It  will  at  once  be  seen  that  the  amount  of  bromine  contained  in 
the  fluid  to  be  analyzed  must  be  known  in  some  measure  before 
this  method  can  be  resorted  to.  As  the  brine  examined  by  FEHL- 
ING  could  contain  at  the  most  *02  grm.  bromine  in  60  grin.,  he 
prepared  ten  different  test  fluids,  by  adding  to  ten  several  portions 
of  60  grm.  each  of  a  saturated  solution  of  common  salt  increasing 
quantities  of  potassium  bromide,  containing  respectively  from  -002 
grm.  to  '020  grm.  bromine.  He  added  an  equal  volume  of  ether 
to  the  test  fluids,  and  then  chlorine  water,  until  there  was  no  fur- 
ther darkening  observed  in  the  color  of  the  ether.  It  being  of  the 
highest  importance  to  hit  this  point  exactly,  since  too  little  as  well 
as  too  much  chlorine  makes  the  color  appear  lighter,  FEHLING  pre- 
pared three  samples  of  each  test  fluid,  and  then  chose  the  darkest 
of  them  for  the  comparison.  60  grm.  are  now  taken;):  of  the 
mother  liquor  to  be  examined,  the  same  volume  of  ether  added  as 
was  added  to  the  test  fluids,  and  then  chlorine  water.  Every 
experiment  is  repeated  several  times.  Direct  sunlight  must  be 
avoided,  and  the  operation  conducted  with  proper  expedition.  In 
my  opinion  it  is  well  to  replace  the  ether  by  chloroform  or  car- 
bon bisulphide.  CAIGNET§  substituted  sodium  hypochlorite  for  the 
chlorine  water,  and  removed  the  colored  carbon  bisulphide  from 
time  to  time. 

II.  Separation  of  Bromine  from  the  Metals. 
The  metallic  bromides  are  analyzed  exactly  like  the  correspond- 
ing chlorides  (§  141,  II.,  a  to  d\  the  whole  of  these  methods  being 


*  Journ.  f.  prakt.  Chem.  36,  184     Proposed  to  effect  the  determination  of 
bromine  in  mother  liquors.  f  Journ.  f  prakt.  Chem.  45,  269. 

\  The  best  way  is  to  take  them  by  measure. 
§  Zeitschr.  f.  anal.  Chem.  9,  427. 


§  145.]  IODINE.  439 

applicable  to  bromides  as  well  as  chlorides.  In  the  decomposition 
of  bromides  by  sulphuric  acid  (§  141,  II.,  d\  porcelain  crucibles 
must  be  used  instead  of  platinum  ones,  as  the  latter  would  be 
attacked  by  the  liberated  bromine.  Some  bromides,  it  must  be 
remembered,  are  not  completely  decomposed  by  sulphuric  acid ; 
for  instance,  mercuric  bromide  is  not.  The  soluble  bromides  may 
be  converted  into  chlorides  by  evaporation  with  hydrochloric  acid 
and  excess  of  chlorine  water ;  but  this  process  cannot  be  applied 
where  the  chloride  is  liable  to  be  carried  away  with  the  steam ;  for 
instance,  in  the  case  of  mercuric  bromide. 

Supplement. 

§  144- 
DETERMINATION  OF  FREE  BROMINE. 

Free  bromine  in  aqueous  solution,  or  evolved  in  the  gaseous 
form,  is  caused  to  act  on  excess  of  solution  of  potassium  iodide. 
Each  at.  bromine  liberates  1  at.  iodine,  which  is  most  conveniently 
determined  by  means  of  sodium  thiosulphate  (§  146).  As  regards 
the  best  mode  of  bringing  about  the  action  of  the  bromine  on  the 
potassium  iodide,  compare  §  142,  1. 

The  determination  of  free  bromine  in  presence  of  hydrobromic 
acid  or  metallic  bromides  is  effected  in  the  same  manner  as  that  of 
free  chlorine  in  presence  of  hydrochloric  acid  (see  §  142). 

§145. 
3.  IODINE. 

I.  Determination* 

a.  Gravimetric  Methods. 

a.  Estimation  as  silver  iodide.  If  yon  have  hydriodic  acid  in 
solution,  free  from  hydrochloric  and  hydrobromic  acids,  precipitate 
with  silver  nitrate,  and  proceed  exactly  as  with  hydrochloric  acid 
(§  141).  If  the  solution  is  colored  with  free  iodine,  first  add 
sulphurous  acid  cautiously  till  the  color  is  removed.  The  particles 
of  silver  iodide  adhering  to  the  filter  are  not  reduced  on  incinera- 
tion, but  a  little  of  the  iodide  is  liable  to  volatilize  if  the  heat  is 

*  For  the  methods  to  be  adopted  in  the  presence  of  bromine  and  chlorine, 
see  §  169. 


440  DETERMINATION.  [§  145. 

too  high.  Hence  the  filter  should  be  got  as  clean  as  possible,  and 
the  heat  during  incineration  should  not  be  unduly  raised.  For  the 
properties  of  silver  iodide,  see  §  94,  3.  The  results  are  perfectly 
accurate. 

/?.  Estimation  as  palladious  iodide.  The  following  method, 
recommended  first  by  LASSAIGNE,  is  resorted  to  exclusively  to  effect 
the  separation  of  iodine  from  chlorine  and  bromine,  for  which  pur- 
pose it  is  extremely  well  adapted.  The  solution  may  not  contain 
any  alcohol.  Acidify  it  slightly  with  hydrochloric  acid,  and  add  a 
solution  of  palladious  chloride,  as  long  as  a  precipitate  forms ;  let 
the  mixture  stand  from  24  to  48  hours  in  a  warm  place,  filter  the 
brownish-black  precipitate  off  on  a  weighed  filter,  wash  with  warm 
water,  and  dry  at  100°,  until  the  weight  remains  constant.  For 
the  properties  of  the  precipitate,  see  §  94,  3.  This  method  gives 
very  accurate  results.  Instead  of  simply  drying  the  palladious 
iodide,  and  weighing  it  in  that  form,  you  may  ignite  it  in  a  current 
of  hydrogen  in  a  crucible  of  porcelain  or  platinum,*  and  calculate 
the  iodine  from  the  residuary  palladium  (H.  ROSE).  Compare 
§  122,  1. 

b.  Volumetric  Methods. 

a.  The  methods  given  for  hydrochloric  acid  by  precipitating 
with  silver  solution  (§  141,  I.,  J,  or),  and  by  silver  solution  and 
iodide  of  starch  (§  141,  I.,  J,  /?),  may  be  used  for  hydriodic  acid 
and  alkali  iodides ;  the  absence  of  chlorine  and  bromine  being  of 
course  presupposed. 

(3.  With  nitrous  acid  and  carbon  disulphide.  This  excellent 
method  has  been  in  frequent  use  in  my  laboratory  for  a  length  of 
time  ;  it  may  be  used  for  small  or  large  quantities  of  iodine.  We 
require : 

aa.  Solution  of  potassium  iodide  of  known  strength.  Made  by 
drying  the  pure  salt  at  180°  (see  p.  121)  and  dissolving  an  exactly 
weighed  quantity  (about  5  grm.)  to  1  litre. 

bb.  Solution  of  sodium  thiosulphate  containing  about  13  or  13*5 
grm.  of  the  pure  crystallized  salt  in  1  litre. 

cc.  Solution  of  nitrous  acid  in  sulphuric  acid.  Prepared  by 
passing  nitrous  acid  gas  into  sulphuric  acid  to  saturation. 

dd.  Pure  carbon  disulphide. 

ee.  Solution  of  sodium  hydrogen  carbonate.     Made  by  dissolv- 


*  This  substance  is  not  injured  by  the  operation. 


§  145.]  IODINE.  441 

ing  5  grm.  in  1000  c.c.  cold  water  and  adding  1  c.c.  of  hydrochloric 
acid  to  the  solution. 

Begin  by  standardizing  the  thiosulphate  as  follows:  Take  a 
well-stoppered  bottle  of  about  400  c.c.  capacity,  transfer  to  it  50 
c.c.  of  the  potassium  iodide  solution,  add  about  150  c.c.  water,  20 
c.c.  carbon  disulphide,  some  dilute  sulphuric  acid,  and  10  drops  of 
the  solution  of  nitrous  acid  in  sulphuric  acid.  Insert  the  stopper 
and  shake  the  bottle  violently  for  some  time,  allow  to  settle,  and 
ascertain  by  adding  a  few  more  drops  of  the  nitrous  acid  that  the 
whole  of  the  iodine  has  been  liberated.  Shake  again,  allow  to 
settle,  and  pour  the  supernatant  fluid  as  completely  as  possible 
into  a  flask,  leaving  the  carbon  disulphide  in  the  bottle,  add  200 
c.c.  water  to  the  latter,  shake  well,  pour  off  the  water  into  the  flask 
and  repeat  the  washing  till  the  last  water  has  no  acid  reaction.  To 
the  contents  of  the  flask  add  10  c.c.  carbon  disulphide,  shake  well, 
pour  off  into  a  second  flask,  wash  the  disulphide  a  little,  and  finally 
shake  the  contents  of  the  second  flask  again  with  some  fresh  disul- 
phide, which  should  now  be  barely  tinged.  Collect  the  disulphide 
from  both  flasks  on  a  filter  moistened  with  water,  wash  it  till  the 
washings  are  no  longer  acid,  place  the  funnel  in  the  bottle  and 
pierce  the  point  of  the  filter  so  that  the  disulphide  from  all  the 
operations  may  be  mixed.  Add  30  c.c.  of  the  sodium  hydrogen 
carbonate  and  then  the  thiosulphate  from  a  burette,  with  continual 
shaking,  till  the  disulphide  has  lost  its  color.  The  number  of  c.c. 
of  thiosulphate  used  will  correspond  to  the  iodine  in  50  c.c.  of 
potassium  iodide  solution. 

The  analysis  is  performed  exactly  as  above.  The  thiosulphate 
requires  to  be  standardized  before  every  fresh  series  of  experi- 
ments, as  it  is  liable  to  slight  alteration.  The  presence  of  chlorides 
has  no  influence  whatever  on  the  results.  In  determining  minute 
quantities  of  iodine  let  the  solutions  be  ten  times  weaker,  and  use 
smaller  quantities  and  smaller  vessels. 

The  results  are  entirely  concordant  and  exact. 

y.  By  distillation  with  ferric  chloride  (DUFLOS).  When  hydri- 
odic  acid  or  a  metallic  iodide  is  heated  in  a  retort  with  solution 
of  pure  ferric  chloride,  the  whole  of  the  iodine  escapes  with  the 
aqueous  vapor,  and.  ferrous  chloride  is  formed  (Fe2Cl6  -(-  2HI  = 
2FeCla  -f-  2HC1  -j-  21).  The  iodine  passing  over  is  received  in 
solution  of  potassium  iodide  and  determined  by  sodium  thiosul- 
phate, as  directed  §  146.  In  employing  this  method  it  must  be 


442  DETERMINATION.  [§  143. 

borne  in  mind  that  the  ferric  chloride  must  be  free  from  chlorine 
and  nitric  acid.  It  is  best  to  prepare  it  from  ferric  oxide  and 
hydrochloric  acid.  We  must  not  forget  too  that  the  separated 
iodine  is  liable  to  act  on  cork  and  caoutchouc ;  the  apparatus 
should  therefore  be  constructed  according  to  fig.  64,  p.  435. 

6.  H.  STRUVE'S  colorimetric  method  may  be  used  in  many  cases. 
In  this  method  the  amount  of  iodine  is  estimated  by  the  depth  of 
color  which  the  separated  iodine  gives  to  a  measured  quantity  of 
carbon  di sulphide. 

II.  Separation  of  Iodine  from  the  Metals. 

The  metallic  iodides  are  in  general  analyzed  like  the  corre- 
sponding chlorides.  From  iodides  of  the  alkali  metals  containing 
free  alkali  the  iodine  may  be  precipitated  as  silver  iodide,  by  first 
saturating  the  free  alkali  almost  completely  with  nitric  acid,  then 
adding  solution  of  silver  nitrate  in  excess,  and  finally  nitric  acid  to 
strongly  acid  reaction.  If  an  excess  of  acid  were  added  at  the 
beginning,  free  iodine  might  separate,  which  is  not  converted  com- 
pletely into  silver  iodide  by  solution  of  silver  nitrate.  In  com- 
pounds soluble  in  water  the  iodine  may  generally  be  precipitated 
as  palladious  iodide ;  you  may  also  determine  the  base  in  one  por- 
tion (decomposing  the  compound  with  concentrated  sulphuric  acid) 
and  the  iodine  in  another  portion  according  to  I.,  J,  y. 

Iodine  cannot  be  separated  from  platinum  directly  with  silver 
nitrate,  as  insoluble  platinum  salts  would  be  thrown  down  with  the 
silver  iodide.  For  this  purpose  H.  TOPSOE*  recommends  the  fol- 
lowing process :  Dissolve  the  substance  in  a  good  amount  of  water, 
.add  solution  of  sodium  hydrogen  sulphite  and  sulphurous  acid, 
heat  on  a  water-bath  till  the  color  has  entirely  disappeared,  and  the 
platinum  is  consequently  converted  into  platinous  sulphite.  In 
this  operation  a  white  flocculent  precipitate  of  sodium  platinous 
sulphite  which  is  difficultly  soluble  separates ;  it  redissolves  on 
addition  of  sulphurous  acid.  After  heating  on  the  water-bath  for 
.some  time,  allow  to  cool  completely,  precipitate  with  silver  solu- 
tion, which  should  not  be  added  in  large  excess,  add  nitric  acid, 
heat  for  about  an  hour  to  redissolve  the  silver  sulphite  first  thrown 
•down  with  the  iodide,  and  then  filter  off  the  latter.  Occasionally 
it  is  to  be  preferred  to  add  sulphurous  acid  instead  of  the  sulphite, 
and  ftien,  when  the  fluid  has  been  heated  and  the  color  has  gone, 

*  Zeitschr.  f .  anal.  Chem.  9,  30. 


§  146.]  IODINE.  443 

to  add  an  excess  of  ammonia.  In  this  way  the  platinum  compound 
is  not  thrown  down,  and  the  silver  sulphite  does  not  separate  after 
the  addition  of  silver  solution  till  nitric  acid  is  added,  and  is  imme- 
diately redissolved  by  the  excess  of  the  same. 

For  the  analysis  of  insoluble  iodides,  especially  silver  and  lead 
iodides,  mercurous  and  cuprous  iodides,  E.  MEUSEL*  strongly 
recommends  sodium  thiosulphate,  in  which  these  salts  dissolve. 
Yery  little  water  should  be  used,  and  as  small  a  quantity  of  the 
thiosulphate  as  possible.  The  metal  is  precipitated  from  the  solu- 
tion by  ammonium  sulphide  in  the  form  of  sulphide.  Evaporate 
the  filtrate  with  soda,  and  heat  the  residue  in  a  platinum  dish  to 
incipient  redness  to  destroy  sodium  thiosulphate  and  tetrathionate. 
Dissolve  the  fusion  in  water  by  the  aid  of  heat,  and  determine  the 
iodine  in  it  by  L,  5,  y.  A  large  quantity  of  ferric  chloride  will  be 
required  to  decompose  the  sodium  sulphite ;  the  residue  in  the 
retort  should  have  a  deep  reddish-brown  color. 

Silver  iodide  may  be  decomposed  also  by  fusing  with  sodium 
carbonate,  but  not  by  igniting  in  a  current  of  hydrogen,  and  not 
completely  by  zinc  or  iron*  Mercurous  iodide  may  be  easily 
decomposed  by  distilling  with  8  or  10  parts  of  a  mixture  of  1  part 
potassium  cyanide  and  2  parts  quicklime.  For  the  apparatus,  see 
fig.  54,  p.  307 ;  db  is  filled  with  magnesite  (II.  KosE-f).  Palladi- 
ous  iodide  may  be  decomposed  by  igniting  in  hydrogen.  Cuprous 
iodide  and  many  other  iodides  may  be  decomposed  by  boiling  with 
potassium  or  sodium  carbonate.  Portions  of  metal,  which  may 
pass  into  the  alkaline  solution,  may  be  thrown  down  by  ammonium 
sulphide,  or  by  acidifying  with  acetic  acid,  and  passing  hydrogen 
sulphide. 

Supplement. 

§  146. 
DETERMINATION  OF  FREE  IODINE. 

The  determination  of  free  iodine  is  an  operation  of  great  impor- 
tance in  analytical  chemistry,  since,  as  BUNSEN$  first  pointed  out,  it 
is  a  means  for  the  estimation  of  all  those  substances  which,  when 
brought  in  contact  with  potassium  iodide,  separate  from  the  same 
a  definite  quantity  of  iodine  (e.g.,  chlorine,  bromine,  &c.),  or,  when 

*  Zeitschr.  f.  anal.  Chem.  9,  208.  \  Ib.  2,  1. 

{  Annal.  d.  Chem.  u.  Pharm.  86,  265. 


444  DETERMINATION.  [§  146. 

boiled  with  hydrochloric  acid,  yield  a  definite  quantity  of  chlorine 
(e.g.,  chromic  acid,  peroxide  of  manganese,  &c.).  By  causing  the 
chlorine  produced  to  act  on  potassium  iodide,  we  obtain  the  equiva- 
lent quantity  of  free  iodine. 

Of  the  various  methods  which  have  been  proposed  for  the  esti- 
mation of  free  iodine,  the  oldest  is  that  of  SCHWARZ.*  It  is  based 
upon  the  following  reaction  :  2Na9SaO3  +  21  =  2NaI  +  NaaS4O6. 
24'8  grin,  pure  crystallized  sodium  thiosulphate  are  dissolved  to  1 
litre.  1000  c.c.  of  the  solution  correspond  to  12'685,  i.e.)  to.l  at. 
iodine.  This  solution  is  added  to  the  solution  of  the  substance  in 
potassium  iodide  until  the  fluid  appears  bright  yellow,  3  or  4  c.c. 
thin  and  very  clear  starch-paste  are  then  added,  which  must  pro- 
duce blue  coloratipn,  and  finally  again  sodium  thiosulphate,  until 
the  blue  fluid  is  decolorized. 

This  method,  though  in  itself  excellent,  is  open  to  this  objec- 
tion, that  it  is  difficult  to  obtain  a  solution  of  absolutely  exact  value 
by  weighing  off  sodium  thiosulphate,  as  the  salt  is  not  readily  pro- 
curable in  a  perfectly  pure  and  dry  condition,  and  although  the 
solution  does  not  change  rapidly  or  to  any  great  extent,  it  is  still 
liable  to  gradual  alteration,  especially  under  the  influence  of  light. 

BUNSEN'S  researches  on  the  volumetric  estimation  of  iodine 
cited  above  produced  a  very  important  and  beneficial  effect  on  the 
whole  domain  of  chemical  analysis.  His  process  depends  on  the 
fact  that  when  iodine  comes  in  contact  with  an  aqueous  solution 
of  sulphurous  acid,  a  decomposition  takes  place  in  accordance  with 
the  equation  H2SO3  +  H2O  +  21  =  H2SO4  +  2(HI),  provided  the 
solution  does  not  contain  more  than  *04  to  "05  per  cent,  of  anhy- 
drous sulphurous  acid.  If  the  solution  is  more  concentrated, 
another  reaction  also  takes  place  to  a  greater  or  less  extent — 
namely,  H2SO4  +  2HI  =  H2SO3  +  H2O  +  21. 

In  this  method,  a  solution  of  iodine  in  potassium  iodide  con- 
taining a  known  quantity  of  free  iodine  is  employed,  and  we  com- 
mence by  determining  the  relation  between  it  and  a  sufficiently 
dilute  solution  of  sulphurous  acid.  In  applying  the  method,  the 
iodine  to  be  estimated  is  dissolved  in  potassium  iodide,  the  stand- 
ard sulphurous  acid  is  added  to  decoloration,  then  thin  starch-paste, 
and  finally  standard  iodine  solution  till  the  blue  color  of  iodide  of 
starch  is  just  visible. 

*  Anleit.  zu  Maassanal.  Nachtrftge,  1853,  22. 


§  146  ]  IODINE.  445 

We  calculate  now  the  c.c.  of  iodine  solution  which  correspond 
to  the  sulphurous  acid  employed,  and  deduct  therefrom  the  c.c.  of 
iodine  added  to  destroy  the  excess  of  sulphurous  acid.  The 
remainder  gives  the  number  of  c.c.  of  iodine  solution  which 
contain  a  quantity  of  iodine  equal  to  that  in  the  substance  ana- 
lyzed. 

On  account  of  the  rapidity  with  which  solution  of  sulphurous 
acid  changes,  this  method  is  somewhat  inconvenient,  and  has  given 
place  to  the  following,  which  is  now  universally  employed.  It 
retains  the  basis  of  BDNSEN'S  method,  but  substitutes  sodium  thio- 
sulphate for  sulphurous  acid,  employing  the  reaction  of  SCHWARZ'S 
method.  With  F.  MOHR*  I  give  this  "  combined  method "  the  -. 
preference,  because,  first,  we  are  not  bound  to  a  definite  strength 
of  the  thiosulphate ;  secondly,  the  solution  of  thiosulphate  is  far  less 
affected  by  the  oxygen  of  the  air  than  sulphurous  acid  ;  and  thirdly, 
it  loses  nothing  by  evaporation.  FiNKENEKf  even  says,  that  the 
use  of  thiosulphate  makes  the  method  more  accurate,  his  experi- 
ments having  shown  that  in  using  BUNSEN'S  method  the  results 
differ;  if,  on  one  occasion,  we  add  the  sulphurous  acid  to  the 
iodine,  and,  on  another,  the  iodine  to  the  sulphurous  acid. 

a.  REQUISITES  FOR  THE  COMBINED  METHOD. 

a.  Iodine  solution  of  known  strength.  Dissolve  6'2  to  6'3 
grm.  iodine  with  the  aid  of  about  9  grm.  potassium  iodide  (free 
from  iodic  acid)  to  about  1200  c.c. 

/?.  Solution  of  sodium  thiosulphate.  Dissolve  12' 2  to  12*3 
grm.  of  the  pure  and  dry  salt  to  about  1200  c.c. 

y.  Solution  of  potassium  iodide.  Dissolve  1  part  of  the  salt 
{free  from  iodic  acid)  in  about  10  parts  of  water.  The  solution 
must  be  colorless  and  must  remain  so  immediately  after  the  addi- 
tion of  dilute  sulphuric  or  hydrochloric  acid  (either  must  be  iron- 
free). 

8.  Starch  solution.  Stir  the  purest  starch  powder  gradually 
with  about  100  parts  cold  water  and  heat  to  boiling  with  constant 
stirring.  Allow  to  cool  quietly,  and  pour  off  the  fluid  from  any 
deposit.  The  solution  should  be  almost  clear  and  free  from  all 
lumps.  The  starch  solution  is  best  prepared  fresh  before  each 
series  of  experiments. 


*  Lehrb.  d.  chem. -analy t.  Titrirmethode,  3  Aufl.  256. 

•f  H.  ROSE,  Handb.  d.  anal.  Chem.  6  Aufl.  von  FINKENER,  2,  937. 


446  DETERMINATION.  [§  146. 

I.  PRELIMINARY  DETERMINATIONS. 

a.  Determination  of  the  relation  between  the  Iodine  Solution 
and  Thiosulphate  Solution. 

Fill  two  burettes  with  the  solutions.  Run  20  c.c.  of  the  thio- 
sulphate into  a  beaker,  add  some  water  and  3  or  4  c.c.  starch  solu- 
tion, then  add  the  iodine  till  a  blue  coloration  is  just  produced.  If 
you  have  added  a  drop  too  much,  run  in  one  or  two  drops  more  of 
the  thiosulphate,  and  then  more  cautiously  the  iodine  solution. 
After  a  few  minutes  read  off  the  height  of  the  fluid  in  both  burettes. 
Suppose  we  had  used  20  c.c.  thiosulphate  to  20-2  c.c.  iodine. 

ft.  Exact  Determination  of  the  Iodine  in  the  Solution. 

This  is  done  immediately  before  each  series  of  analyses  with 
the  aid  of  an  exactly  weighed  quantity  of  pure  and  dry  iodine. 
Experience  has  convinced  me  that  solution  of  iodine  in  potassium 
iodide,  even  when  kept  cool  and  in  the  dark,  is  much  more  liable 
to  change  than  is  usually  supposed.* 

The  process  is  conducted  in  the  following  manner :  Select  three 
watch-glasses,  a,  £>,  and  c,  which  fit  each  other;  weigh  J  and  c 
together  accurately.  Put  about  0'5  grm.  pure  dry  iodine  (prepared 
according  to  §  65,  6)  into  «,  place  it  on  an  iron  plate,  heat  gently, 
till  dense  fumes  of  iodine  escape.  Now  cover  it  with  I)  and  regu- 
late the  heat  so  that  the  iodine  may  sublime  entirely  or  almost 
entirely  into  o.  Next  remove  b  while  still  hot,  and  give  it  a  gentle 
swing  in  the  air  to  remove  the  still  uncondensed  iodine  fumes  and 
any  traces  of  aqueous  vapor,  cover  it  with  c,  allow  to  cool  under 
the  desiccator,  weigh  and  transfer  the  two  watch-glasses  together 
with  the  weighed  iodine  to  a  capacious  beaker,  containing  a  suffi- 
cient quantity  of  potassium  iodide  solution  to  dissolve  the  whole  of 
the  iodine  to  a  clear  fluid.  Add  water  and  then  thiosulphate  from 
a  burette  till  the  color  is  gone ;  now  add  3  or  4  c.c.  of  starch-paste 
and  iodine  solution  (a,  <*)  from  a  second  burette  till  a  blue  tinge 
just  appears.  Having  read  off  both  burettes,  the  following  simple 
calculation  will  give  you  the  iodine  in  the  solution  #,  a : 

Suppose  we  had  weighed  off  '150  grm.  iodine,  and  used  29'5 
c.c.  thiosulphate  and  '3  c.c.  iodine  solution. 

*  I  filled  several  small  well-stoppered  bottles  with  some  solution  of  iodine  in 
potassium  iodide,  whose  standard  had  been  accurately  determined,  and  placed 
them  in  a  cellar.  Even  in  the  course  of  a  few  weeks  the  standard  had  altered. 
I  now  never  rely  on  the  strength  of  a  solution  of  iodine,  unless  I  have  determined 
it  shortly  before. 


§  146.]  IODIDE.  447 

From  J,  or,  we  know  that  20  c.c.  thiosulphate  correspond  to 
20*2  c.c.  iodine  solution ;  29*5  c.c.  therefore  correspond  to  29*8  c.c. 

Xow  29-5  c.c.  thiosulphate  correspond  to  '150  grm.  iodine  +  -3 
c.c.  iodine  solution. 

But  29-5  c.c.  thiosulphate  also  correspond  to  29*8  c.c.  iodine 
solution. 

.*.  -150  grm.  iodine  -f-  '3  c.c.  iodine  solution  =  29*8  c.c.  iodine 
solution. 

.*.  -150  grm.  iodine  =  29*5  c.c.  iodine  solution. 

.*.    1  c.c.  iodine  solution  =  -0050847  grm.  iodine. 

The  experiment  just  described  is  repeated  and  the  mean  of  the 
two  results  taken,  provided  they  exhibit  sufficient  uniformity. 

y.  Dilution  of  the  standard  fluids  to  a  convenient  strength. 

With  the  aid  of  the  iodine  solution  the  strength  of  which  we 
now  know  exactly,  and  the  solution  of  sodium  thiosulphate  which 
stands  in  a  known  relation  to  the  same,  we  might  make  any  deter- 
minations of  iodine.  The  calculation,  although  in  principle  ex- 
tremely simple,  is  yet  somewhat  hampered  by  reason  of  the  long 
decimal  which  expresses  the  quantity  of  iodine  in  1  c.c.  of  the 
solution.  It  is  therefore  convenient  to  dilute  the  iodine  solution 
so  that  1  c.c.  may  exactly  contain  -005  grm.  iodine.  This  is  done 
by  filling  a  litre  flask  therewith,  and  adding  the  necessary  quantity 
of  water;  in  our  case  16-94  c.c.,  for  5  :  5-0847  : :  1000  : 1016-94.  If 
the  litre  flask  will  hold  above  the  mark  this  16*94  c.c.,  it  is  simply 
added,  otherwise  it  is  put  into  the  dry  bottle  destined  to  receive 
the  iodine  solution,  the  iodine  solution  added,  the  whole  shaken 
together,  a  portion  of  the  fluid  returned  to  the  flask,  shaken,  poured 
back  into  the  bottle,  and  the  whole  shaken  again. 

The  solution  of  thiosulphate  may  now  be  diluted  in  a  corre- 
sponding manner.     In  our  case  we  should  have  had  to  add  27*11 
c.c.  water  to  1000  c.c.  of  the  solution,  as  will  be  seen  from  the  fol 
lowing  consideration : 

20-2  c.c.  of  the  original  iodine  solution  correspond  to  20  c.c.  of 
the  thiosulphate  solution. 

.-.  1000  c.c.  correspond  to  990-1  c.c. 

Now  these  1000  c.c.  were  made  up  to  1016-94  by  addition  of 
water ;  if  therefore  we  make  up  990*1  c.c.  of  the  sodium  thiosul- 
phate to  the  same  bulk  by  addition  of  water  we  shall  have  equiva- 
lent solutions.  Hence,  to  990-1  c.c.  we  must  add  26*84  c.c.  water, 
or  to  1000  c.c.  27*11  water. 


448  DETERMINATION.  [§  146. 

In  such  cases  of  dilution  I  always  prefer  to  take  exactly  1  litre 
instead  of  an  uneven  number  of  c.c.,  as  in  measuring  the  latter 
errors  and  inaccuracies  may  readily  occur ;  I  have  therefore  above 
recommended  the  preparation  of  1200  c.c.  of  the  fluids,  so  that 
after  their  determination  1000  c.c.  may  be  sure  to  remain. 

c.  THE  ACTUAL  ANALYSIS. 

"Weigh  the  iodine  to  be  determined  in  a  glass-stoppered  tube,  dis- 
solve in  potassium  iodide  solution  as  in  5,  /?,  add  thiosulphate  solution 
from  the  burette  till  decoloration  is  just  produced,  then  3  or  4  c.c. 
starch  solution,  then  iodine  solution  from  a  second  burette  to  incip- 
ient blueness.  The  substance  contains  the  same  amount  of  iodine 
as  the  c.c.  of  iodine  solution  corresponding  to  the  thiosulphate  used 
minus  the  c.c.  of  the  former  used  to  destroy  the  excess  of  the 
latter.  Where  the  solutions  are  of  equal  value  and  1  c.c.  corre- 
sponds to  '005  grm.  iodine,  the  calculation  is  in  the  highest  degree 
simple ;  for  suppose  we  had  used  21  c.c.  Na3SaO3  and  1  c.c.  iodine, 
the  quantity  of  iodine  present  is  '100  grm. 

21  -  1  =  20,  and  20  X  '005  =  -100. 

Where  you  are  analyzing  chromic  acid  or  manganese  dioxide 
by  boiling  with  hydrochloric  acid,  and  passing  the  chlorine  evolved 
into  potassium  iodide,  you  must  allow  the  solution  to  cool  before 
titrating  with  thiosulphate ;  for  at  a  high  temperature  a  portion  of 
the  sodium  tetrathionate  produced  is  converted  into  sodium  sul- 
phate by  the  iodine  (WRIGHT*). 

Free  acid  in  the  iodine  solution  to  be  estimated  is  not  injuri- 
ous ;  when  such  is  present,  however,  the  excess  of  the  thiosulphate 
must  be  titrated  without  delay,  or  the  free  thiosulphuric  acid  may 
be  decomposed  before  the  iodine  is  added. 

d.  KEEPING  OF  THE  SOLUTIONS. 

The  iodine  solution  and  the  thiosulphate  solution  are  kept  in 
glass-stoppered  bottles  in  a  cool,  dark  place.  But  the  relation 
between  the  two  solutions  must  be  tested  before  each  new  series 
of  experiments,  and  the  iodine  in  the  iodine  solution  must  be  rede- 
termined. 

If  a  fluid  contains  free  iodine  in  presence  of  iodine  in  combina- 
tion, determine  the  former  in  one  portion  by  the  combined  method, 
and  the  total  quantity  in  another  portion.  For  this  purpose  you 

*  Zeitschr.  f .  anal.  Chem.  9,  482. 


§  147]  CYANOGEN.  449 

may  either  (1)  add  sulphurous  acid  to  decoloration,  precipitate 
with  silver  nitrate  (§  145,  1.,  #,  or),  digest  the  precipitate  with  nitric 
acid  to  remove  any  silver  sulphite  which  it  may  contain,  filter,  &c.  ; 
or  (2)  distil  with  ferric  chloride  as  directed,  §  145,  I.,  b,  y. 


4.  CYANOGEN.* 

I.  Determination. 

<t.  Gravimetric  Estimation.  —  If  you  have  free  hydrocyanic  acid 
In  solution  run  it  into  an  excess  of  solution  of  silver  nitrate,  add  a 
little  nitric  acid,  allow  to  settle  without  warming,  and  determine 
the  precipitated  silver  cyanide  either  by  collecting  on  a  weighed 
filter,  drying  at  100°  and  weighing  (§  115,  3),  or  by  collecting  on 
an  unweighed  filter  and  converting  into  metallic  silver.  The  latter 
operation  is  performed  by  igniting  the  precipitate  in  a  porcelain 
crucible  for  \  hour,  or  till  it  ceases  to  lose  weight  (H.  ROSE).  If 
you  wish  to  determine  in  this  way  the  hydrocyanic  acid  in  bitter 
almond  water  or  cherry  laurel  water,  add  ammonia  after  the  addi- 
tion of  the  solution  of  silver  nitrate  till  the  fluid  is  strongly  alka- 
line (it  is  not  necessary  to  dissolve  all  the  silver  cyanide),  and  at 
once  acidify  with  nitric  acid.  When  the  precipitate  has  settled, 
filter.  The  whole  of  the  cyanogen  in  the  fluid  will  have  been  now 
converted  into  silver  cyanide.  (The  cyanogen  was  originally  pres- 
ent partly  as  hydrocyanic  acid,  partly  as  ammonium  cyanide,  but 
principally  as  hydrocyanate  of  benzaldehyd  —  S.  FELDHAus.f) 

FELDHAUS  recommends  the  following  proportions  :  100  grm. 
bitter  almond  water,  about  1'2  grm.  silver  nitrate,  dissolved  in 
water  and  2  to  3  c.c.  ammonia  sp.  gr.  *96.  A  portion  of  the  filtrate 
should  be  tested  to  make  sure  that  it  contains  silver  salt  in  excess, 
another  portion  should  be  tested  by  making  it  strongly  alkaline 
with  ammonia,  and  then  acid  again  with  nitric  acid.  If  a  precipi- 
tate is  formed  in  the  latter  case  it  shows  that  the  whole  of  the 
hydrocyanate  of  benzaldehyd  was  not  decomposed,  and  the  precipi- 
tation must  be  repeated.  If  you  want  to  measure  off  a  fluid  con- 
taining hydrocyanic  acid  with  a  pipette,  insert  a  little  tube  with 


*  With  regard  to  HERAPATH'S  colorimetric  method,  which  is  founded  on  the 
intensity  of  the  color  of  a  solution  of  persulphocyanide  of  iron,  compare  Chem. 
Oaz.  Aug.  1853,  294.  t  Zeitschr.  f.  anal.  Chem.  3,  34. 


450  DETERMINATION.  [§  147. 

soda-lime  between  the  pipette  and  the  flexible  tube  which  you  put 
into  your  mouth. 

b.  LIEBIG'S  Volumetric  Method*  '.  —  If  hydrocyanic  acid  is  mixed 
with  potassa  to  strong  alkaline  reaction,  and  a  dilute  solution  of 
silver  nitrate  is  then  added,  a  permanent  turbidity  of  silver  cyanide 
—  or,  if  a  few  drops  of  solution  of  sodium  chloride  have  been  added, 
of  silver  chloride  —  forms  only  after  the  whole  of  the  cyanogen  is 
converted  into  double  cyanide  of  silver  and  potassium.  The  first 
drop  of  solution  of  silver  nitrate  added  in  excess  produces  the  per- 
manent precipitate.  1  at.  silver  consumed  in  the  process  corre- 
sponds, therefore,  exactly  to  2  mol.  hydrocyanic  acid  (2KCy  -f-  Ag 
NO3  =  AgCy.KCy  -f-  KNO8).  A  decinorrnal  solution  of  silver 
nitrate,  containing  consequently  10*793  grm.  silver  in  the  litre, 
should  be  used  ;  1  c.c.  of  this  solution  corresponds  to  '005408  of 
hydrocyanic  acid.  In  examining  medicinal  hydrocyanic  acid,  5  to 
10  grm.  ought  to  be  used,  but  of  bitter  almond  water  about  50 
grm.  ;  if  exactly  5*408  or  54*08  grm.  are  used,  the  number  of  c.c. 
of  the  silver  solution,  divided  by  10,  or  by  100,  expresses  exactly 
the  percentage  of  hydrocyanic  acid.  Medicinal  hydrocyanic  acid 
is  suitably  diluted  first  by  adding  from  5  to  8  volumes  of  water  ; 
bitter  almond  water  also  is  slightly  diluted  ;  if  the  latter  is  turbid 
the  end-reaction  will  not  be  sufficiently  distinct,  and  the  gravimetric 
method  is  to  be  preferred. 

LIEBIG  has  examined  hydrocyanic  acid  of  various  degrees  of  dilu- 
tion, and  has  obtained  results  by  this  method  corresponding  exactly 
with  those  obtained  by  a.  SoucHAY,f  too,  obtained  results  almost 
identical  ;  with  pure  dilute  hydrocyanic  acid,  the  gravimetric  results 
were  to  the  volumetric  as  100  to  100*5  —  101  ;  with  clear  or  nearly 
clear  bitter  almond  water  as  100  to  102.  FELDHAUS  (loc.  cit.) 
obtained  very  nearly  similar  results.  The  slightly  higher  results 
of  the  volumetric  process  are  to  be  explained  from  the  fact  that  a 
small  excess  of  silver  solution  is  necessary  to  produce  the  final 
reaction.  The  less  the  amount  of  the  substance  taken  the  greater 
importance  does  this  error  assume.  We  should  also  notice  that  in 
'the  bitter  almond  water,  which  contains  ammonium  cyanide,  some 
ammonia  is  set  free  which  has  a  solvent  action  on  the  silver  cyanide. 
In  this  method  it  does  not  matter  whether  the  hydrocyanic  acid 


*  Annal.  d.  Chem.  u.  Pharm.  77,  102. 
f  Zeitschr.  f.  anal.  Chem.  2,  180. 


§  147]  CYANOGEN.  451 

contains  an  admixture  of  hydrochloric  acid  or  formic  acid.    A  con- 
siderable excess  of  potassa  must  be  avoided. 

If  it  is  intended  to  determine  potassium  cyanide  by  this  method, 
a  solution  of  that  salt  must  be  prepared  of  known  strength,  and  a 
measured  quantity  used  containing  about  '1  grm.  of  the  salt. 
Should  it  contain  potassium  sulphide,  a  small  quantity  of  freshly 
precipitated  lead  carbonate  must  be  first  added,  and  the  solution 
filtered  before  proceeding  to  the  determination. 

II.  Separation  of  Cyanogen  from  the  Metals. 

a.  In  Cyanides  of  the  Alkali  Metals. 

Mix  the  substance  (if  solid,  without  previous  solution  in  water) 
with  excess  of  silver  nitrate  solution,  then  add  water,  finally  nitric 
acid  in  slight  excess,  allow  to  settle  without  warming,  and  deter- 
mine the  silver  cyanide  as  in  I.,  a.  The  basic  metals  are  deter- 
mined in  the  filtrate  after  separating  the  excess  of  silver. 

J.  In  Cyanides  and  double  Cyanides,  which  are  completely 
decomposed  l>y  Silver  Nitrate  and  Nitric  Acid  or  Silver  Nitrate 
and  Ammonia. 

Digest  for  some  time  with  a  dilute  solution  of  silver  nitrate, 
stirring  frequently,*  then  add  nitric  acid  in  moderate  excess,  and 
digest  at  a  gentle  heat,  till  the  foreign  cyanide  is  fully  dissolved 
and  the  silver  cyanide  has  become  pure  and  quite  white.  Then 
add  water  and  filter.  As  a  precautionary  measure  it  is  well  to  test 
the  metal  obtained  by  long  ignition  of  the  silver  cyanide,  whether 
it  is  free  from  those  metals  which  were  combined  with  the  cyano- 
gen. The  filtrate  is  used  for  estimating  the  basic  metals,  the  silver 
being  first  precipitated  with  hydrochloric  acid.  This  method  affords 
us  an  exact  analysis  of  the  double  cyanides  of  potassium  with 
nickel,  copper,  and  zinc  (H.  ROSE). 

~W.  WEiTnf  recommends  a  solution  of  silver  nitrate  in  ammo- 
nia for  the  decomposition  of  many  cyanogen  compounds,  such  as 
potassium  ferrocyanide,  Prussian  blue,  and  even  potassium  cobalti- 
cyauide.  He  digests  them  in  sealed  tubes  at  100°  (in  the  case  of 
potassium  cobalticyanide,  150°)  for  4  or  5  hours.  Warm  the  con- 
tents of  the  tube  gently  in  a  dish,  until  the  crystals  of  ammonio- 
cyanide  of  silver  are  dissolved,  filter  off  the  separated  metallic 

*  Double  cyanide  of  Dickel  and  potassium  yields  by  this  process  a  mixture  of 
silver  cyanide  with  nickel  cyanide.  Like  double  cyanides  are  similarly  decom- 
posed, f  Zeitschr.  f.  anal.  Chem.  9,  379. 


452  DETEKMINATION.  [§  147. 

oxide,  wash  it  with  ammonia,  dilute,  and  precipitate  the  silver 
cyanide  by  acidifying  with  nitric  acid.  In  the  filtrate  separate  the 
silver  from  the  alkalies,  &c.  In  respect  to  the  undissolved  oxides 
it  should  be  noted  that  metallic  silver  is  always  mixed  with  the 
ferric  oxide. 

c.  In  Mercuric  Cyanide. 

Precipitate  the  aqueous  solution  with  hydrogen  sulphide ;  the 
mercuric  sulphide  may  be  filtered  without  difficulty  if  a  little 
ammonia  or  hydrochloric  acid  be  added ;  it  is  determined  accord- 
ing to  §  118,  3.  If  the  compound  is  in  the  solid  condition,  the 
cyanogen  may  be  determined  in  another  portion  by  ignition  with 
cupric  oxide,  the  nitrogen  and  carbonic  acid  being  collected  and 
separated  (comp.  Organic  Analysis). 

H.  HOSE  and  FINKENER*  have,  after  much  trouble,  succeeded 
in  finding  out  a  method  for  determining  cyanogen  with  precision 
also  in  solutions  of  mercuric  cyanide.  Mix  the  solution  of  the  mer- 
curic cyanide  with  zinc  nitrate  dissolved  in  ammonia.  To  1  part 
of  mercuric  salt  you  may  add  about  2  parts  of  the  zinc-salt.  Add 
to  the  clear  solution  hydrogen  sulphide  water  gradually  till  it  pro- 
duces a  perfectly  white  precipitate  of  zinc  sulphide.  The  precipi- 
tate, which  is  a  mixture  of  the  mercuric  and  zinc  sulphides,  settles 
well.  After  a  quarter  of  an  hour  filter  it  off  and  wash  with  very 
dilute  ammonia.  The  filtrate  contains  zinc  cyanide  dissolved  in 
ammonia,  together  with  ammonium  nitrate.  It  does  not  smell  of 
hydrocyanic  acid,  and  consequently  no  escape  of  the  latter  takes 
place.  Mix  it  with  silver  nitrate  and  then  add  dilute  sulphuric  acid 
in  excess.  The  silver  cyanide  is  next  washed  a  little  by  decantation, 
then — to  free  it  from  any  zinc  cyanide  simultaneously  precipitated 
—heated  with  a  solution  of  silver  nitrate,  finally  filtered  off, 
washed,  and  determined  after  I.,  a.  The  precipitated  sulphides 
may  be  dissolved  in  aqua  regia,  and  the  mercury  precipitated  as 
mercurous  chloride  according  to  §  118,  2.  The  test-analyses  com- 
municated by  ROSE  yielded  excellent  results. 

d.  In  compounds  decomposable  by  Mercuric  Oxide  in  the  Wet 
Way. 

Many  simple  cyanides,  and  also  double  'cyanides — both  of  the 
character  of  the  double  cyanide  of  nickel  and  potassium,  and  of 
the  ferro-  or  ferricyanides  (not,  however,  cobalticyanides) — may,  as 

*  Zeitschr.  f.  anal.  Chem.  1,  288. 


§  147]  CYANOGEN.  453 

is  well  known,  be  completely  decomposed  by  boiling  with  excess 
of  mercuric  oxide  and  water,  all  cyanogen  being  obtained  as  mer- 
curic cyanide  and  the  metals  passing  into  oxides. 

H.  HOSE  (loc.  cit.)  has  shown  that  Prussian  blue,  potassium 
ferro-  and  ferricyanide,  more  particularly,  may  be  readily  analyzed 
in  this  manner. 

Boil  a  few  minutes  with  water  and  excess  of  mercuric  oxide  till 
complete  decomposition  is  effected,  add — in  order  to  render  the 
ferric  hydroxide  and  mercuric  oxide  removable  by  filtration — nitric 
acid  in  small  portions,  till  the  alkaline  reaction  has  nearly  disap- 
peared, filter,  wash  with  hot  water,  dry  the  precipitate,  ignite — 
very  gradually  raising  the  heat — under  a  hood  (with  a  good 
draught),  and  weigh  the  ferric  oxide  remaining.  In  the  filtrate 
the  cyanogen  is  determined  according  to  c,  and  any  potassium  that 
may  be  present  is  determined  in  the  filtrate  from  the  silver  cya- 
nide. 

e.  Determination  of  Metals  contained  in  Cyanides  with  decom- 
position and  volatilization  of  the  Cyanogen. 

Of  the  various  means  for  completely  decomposing  compounds 
of  cyanogen,  especially  also  the  double  cyanides,  according  to  H. 
ROSE  (loc.  cit.)  three  particularly  are  worthy  of  recommendation — 
viz.,  concentrated  sulphuric  acid,  mercuric  sulphate,  and  ammo- 
nium chloride.  The  nitrates  seemed  decidedly  less  suitable  on 
account  of  their  too  violent  action. 

a.  DECOMPOSITION  BY  SULPHURIC  Aero.  All  cyanogen  com- 
pounds, simple  or  double,  are  completely  decomposed  and  con- 
verted into  sulphates  or  oxides,  as  the  case  may  be,  if  treated  in  a 
powdered  condition  in  a  platinum  dish  or  a  capacious  platinum 
crucible  with  a  mixture  of  about  3  parts  concentrated  sulphu- 
ric acid  and  1  part  water,  and  heated  till  almost  all  the  sulphuric 
acid  had  been  expelled.  The  residual  mass  is  then  free  from  cyan- 
ogen. It  is  dissolved  in  water,  if  necessary  with  addition  of 
hydrochloric  acid,  and  the  metals  determined  by  the  usual  methods. 
This  way  is  not  adapted  for  mercuric  cyanide,  as  a  little  of  the 
metal  would  escape  with  the  fumes  of  the  sulphuric  acid. 

ft.  DECOMPOSITION  BY  MERCURIC  SULPHATE.  Of  the  mercuric 
sulphates,  those  suitable  to  our  present  purpose  are  the  normal  and 
the  basic  (Turpeth  mineral).  The  substance  is  mixed  with  fi  parts 
of  the  latter,  heated  in  a  platinum  crucible  gradually,  and  finally 
maintained  for  a  long  time  at  a  red-heat,  till  all  the  mercurv  has 


454  DETERMINATION.  [§  147. 

volatilized,  and  the  weight  of  the  crucible  remains  constant.  If 
alkalies  are  present,  a  little  ammonium  carbonate  is  added  during 
the  final  ignition,  from  time  to  time,  in  order  to  convert  the  acid 
sulphates  into  normal.  The  residue  may  usually  be  analyzed  by  sim- 
ple treatment  with  water ;  in  the  case  of  potassium  f errocyanide, 
for  instance,  the  potassium  sulphate  dissolves,  and  pure  (alkali-free) 
ferric  oxide  remains  behind.  The  test-analyses  that  have  been 
communicated  yielded  excellent  results. 

y.  DECOMPOSITION  BY  AMMONIUM  CHLORIDE.  Mix  the  substance 
with  twice  or  thrice  the  amount  of  this  salt,  and  ignite  the  mixture 
moderately  in  a  stream  of  hydrogen  (apparatus,  p.  251,  fig.  5(W^). 
From  the  cooled  mass  water  extracts  alkaline  chloride,  while  the 
reducible  metals  remain  in  the  metallic  state.  The  method  is 
peculiarly  adapted  for  the  analysis  of  double  cyanide  of  nickel  and 
potassium  and  cobalticyanide  of  potassium,  not  so  for  iron  com- 
pounds, since  the  iron  obtained  is  not  pure,  but  contains  carbon. 

If  one  of  the  methods  described  in  e  is  employed,  the  nitrogen 
and  carbon  (the  cyanogen)  must  be  determined  by  a  combustion, 
if  an  estimation  by  the  loss  is  not  sufficient. 

f.  Determination  -of  the-  Alkalies,  especially  of  Ammonia  in 
Soluble  Ferrocyanides. 

Mix  the  boiling  solution  with  a  solution  of  cupric  chloride,  in 
moderate  excess,  filter  off  the  precipitated  cupric  f  errocyanide,  free 
the  filtrate  from  copper  by  means  of  hydrogen  sulphide,  and  then 
determine  the  alkalies  (REINDEL*). 

g.  Volumetric  Determination  of  Ferro-  and  Ferricyanogen. 

a.  After  E.  DE  HAEN.  This  method,  devised  in  my  laboratory, 
is  founded  upon  the  simple  fact  that  a  solution  of  potassium  ferro- 
cyanide  acidified  with  sulphuric  acid  (and  which  may  accordingly 
be  assumed  to  contain  free  hydroferrocyanic  acid)  is  by  addition 
of  potassium  permanganate  converted  into  the  corresponding  ferri- 
cyanide.  If  this  conversion  is  effected  in  a  very  dilute  fluid,  con- 
taining about  '2  grm.  potassium  ferrocyanide  in  from  100  to  200 
c.c.,  the  termination  of  the  reaction  is  clearly  and  unmistakably 
indicated  by  the  change  of  the  originally  pure  yellow  color  of  the 
fluid  to  reddish-yellow,  f 

*  Journ.  f.  prakt.  Chem.  65,  452. 

f  Instead  of  the  permanganate  you  may  use  chromate  of  potash.  The  solu- 
tion is  added  till  spots  of  sesquicbloride  of  iron  on  a  plate  are  no  longer  colored 
blue  or  green,  but  brownish.  E.  MEYER,  Zeitschr.  f.  anal.  Chem.  8,  508. 


§  147]  CYANOGEN.  455 

The  process  requires  two  test-fluids  of  known  strength,  viz. : 

1.  A  solution  of  pure  potassium  ferrocyanide. 

2.  A  solution  of  potassium  permanganate. 

The  former  is  prepared  by  dissolving  20  grin,  perfectly  pure 
and  dry  crystallized  potassium  ferrocyanide  in  water  to  1  litre ; 
each  c.c.  therefore  contains  20  mgrm.  The  latter  is  diluted  so  that 
somewhat  less  than  a  buretteful  is  required  for  10  c.c.  of  the  solu- 
tion of  potassium  ferrocyanide. 

To  determine  the  strength  of  the  potassium  permanganate  solu- 
tion in  its  action  upon  the  potassium  ferrocyanide,  measure  off,  by 
means  of  a  pipette,  10  c.c.  of  the  solution  of  potassium  ferrocyanide 
(containing  '2  grm.),  dilute  with  100  to  200  c.c.  water,  acidify  with 
sulphuric  acid,  place  the  glass  on  a  sheet  of  white  paper,  and  allow 
the  permanganate  to  drop  into  the  fluid,  stirring  it  at  the  same 
time,  until  the  change  from  yellow  to  reddish-jellow  indicates  that 
the  conversion  is  complete.*  Repetitions  of  the  experiment  always 
give  very  accurately  corresponding  results.  If  at  any  time  you 
have  reason  to  suspect  that  the  permanganate  has  suffered  altera- 
tion, recourse  must  be  had  again  to  this  experiment.  If  after 
acidifying  the  potassium  ferrocyanide  with  sulphuric  acid  you  add 
a  trace  of  ferric  chloride  to  produce  a  bluish-green  color,  the  latter 
will  disappear  at  the  end  of  the  reaction,  which  is  thus  rendered 
very  distinct  (GrnTLf). 

To  determine  the  amount  of  real  potassium  ferrocyanide  con- 
tained in  any  given  sample  of  the  commercial  article,  dissolve  5 
grm.  to  250  c.c. ;  take  10  c.c.  of  this  solution,  and  examine  as  just 
directed.  Suppose,  in  determining  the  strength  of  the  permanga- 
nate, you  have  used  20  c.c.,  and  you  find  now  that  19  c.c.  is  suffi- 
cient, the  simple  rule-of -three  sum, 

20  :  -2  : :  19  :  x 

will  inform  you  how  much  pure  potassium  ferrocyanide  *2  grm.  of 
the  analyzed  salt  contains.  And  even  this  small  calculation  may 
be  dispensed  with,  by  diluting  the  permanganate  so  that  exactly 
50  c.c.  correspond  to  *2  of  potassium  ferrocyanide,  as,  in  that  case, 

*  If  you  wish  at  first  for  some  additional  evidence  besides  the  change  of  color, 
add  to  a  drop  of  the  mixture  on  a  plate,  a  drop  of  solution  of  sesquichloride  of 
iron :  if  this  fails  to  produce  a  blue  tint,  the  conversion  is  accomplished. 

•j-  Zcitschr.  f.  anal.  Chem.  6,  446. 


456  DETERMINATION.  [§  147. 

the  number  of  half-c.c.  consumed  expresses  directly  the  percentage 
of  pure  ferrocyanide. 

Instead  of  determining  the  strength  of  the  permanganate  by 
means  of  pure  potassium  ferrocyanide,  which  is  unquestionably 
the  best  way,  one  of  the  methods  given  in  §  112,  2,  may  also  be 
employed  ;  bearing  in  mind,  in  that  case,  that  2  mol.  potassium 
ferrocyanide  —  885*52,  2  at.  iron  =  112,  and  1  mol.  oxalic  acid  — 
126  are  equivalent  in  their  action  up6n  solution  of  potassium  per- 
manganate. 

The  analysis  of  soluble  ferricyanides  by  this  method  is  effected 
by  reducing  them  to  ferrocyanides,  acidifying,  and  then  proceeding 
in  the  way  described.  The  reduction  is  effected  as  follows  :  Mix 
the  weighed  ferricyanide  with  a  solution  of  soda  or  potassa  in 
excess,  boil  and  add  concentrated*  solution  of  ferrous  sulphate 
gradually,  and  in  small  portions,  until  the  color  of  the  precipitate 
appears  black,  which  is  a  sign  that  protosesquioxide  of  iron  has 
precipitated.  Dilute  now  to  300  c.c.,  mix,  filter,  and  proceed  to 
determine  the  ferrocyanide  in  portions  of  50  or  100  c.c.  of  the 
lluid.  As  the  space  occupied  by  the  precipitate  is  not  taken  into 
account  in  this  process,  the  results  are  not  absolutely  accurate  ;  the 
difference  is  so  very  trifling,  however,  that  it  may  safely  be  disre- 
garded. GINTL  (loc.  cit.)  suggests  to  put  the  neutral  or  alkaline 
fluid  in  a  tall  vessel  and  add  a  few  lumps  of  sodium  amalgam  as 
big  as  peas  :  in  ten  minutes  the  reduction  will  be  effected  and  with- 
out the  aid  of  heat. 

Insoluble  ferro-  or  ferricyanides,  decomposable  by  boiling  solu- 
tion of  potassa  (as  are  most  of  these  compounds),  are  analyzed  by 
boiling  a  weighed  sample  sufficiently  long  with  an  excess  of  solu- 
tion of  potassa  (adding,  in  the  case  of  ferricyanides,  ferrous  sul- 
phate), and  then  proceeding  as  directed  above. 

ft.  After  E.  BOHLIG.* 

In  the 'case  of  a  fluid  containing  potassium  ferrocyanide,  and 
also  sulphocyanide  (for  instance,  the  red  liquor  of  the  prussiate 
works),  the  method  given  in  a  cannot  be  employed,  as  the  hydro- 
sulphocyanic  acid  also  reduces  permanganic  acid.  The  following 
method — depending  on  the  precipitation  of  the  ferrocyanogen  with 
solution  of  cupric  sulphate — may  then  be  used ;  it  is  accurate 
enough  for  technical  purposes.  Dissolve  10  grm.  pure  cupric  sul- 


*  Polyteclm.  Notizblatt,  16,  81. 


§  148.]  SULPHUR.  457 

phate  to  1  litre^also  4  grin,  pure  dry  potassium  ferrocyanide  to  1 
litre.  Add  to  50  c.c.  of  the  latter  solution  (which  contain  -2  grm. 
potassium  ferrocyanide)  copper  solution  from  a  burette  to  complete 
precipitation  of  the  ferrocyanogen.  In  order  to  hit  this  point 
exactly,  from  time  to  time  dip  a  strip  of  filter-paper  into  the 
browriish-red  fluid  which  will  imbibe  the  clear  filtrate,  leaving  the 
precipitate  of  copper  ferrocyanide  behind.  At  first  the  moist  strips 
of  paper,  when  touched  with  ferric  chloride,  become  dark  blue,  the 
reaction  gradually  gets  weaker  and  weaker,  and  finally  vanishes 
altogether.  We  now  know  the  value  of  the  copper  solution  with 
reference  to  its  action  on  potassium  ferrocyanide,  and  can,  there- 
fore, by  its  means  test  solutions  containing  unknown  amounts  of 
ferrocyanogen.  If  alkali  sulphides  are  present,  they  are  first 
removed  by  boiling  with  lead  carbonate.  After  filtering  off  the 
lead  sulphide,  acidify  with  dilute  sulphuric  acid,  and  then  proceed. 

§148. 

5.    SULPHUK. 

I.  Determination. 

To  determine  hydrogen  sulphide  in  a  mixture  of  gases  confined 
over  mercury*  it  may  be  absorbed  by  a  ball  made  of  2  parts  precipi- 
tated lead  phosphate  and  3  parts  plaster  of  Paris.  The  mixture  is 
made  into  a  paste  with  water,  and  pressed  into  a  bullet  mould  in 
which  the  platinum  wire  is  inserted.  The  mould  should  previously 
be  oiled.  The  balls  are  dried  at  100°,  saturated  with  concentrated 
phosphoric  acid,  and  are  then  ready  for  use  (LuDwiat). 

To  determine  sulphuretted  hydrogen  dissolved  in^water  the 
following  methods  are  in  use : 

a.  The  method  of  determining  hydrogen  sulphide  volumetri- 
cally  by  solution  of  iodine,  was  employed  first  by  DUPASQUIER  ;  it 
is  very  convenient  and  accurate.  That  chemist  used  alcoholic  solu- 
tion of  iodine.  But  as  the  action  of  the  iodine  upon  the  alcohol 
alters  the  composition  of  this  solution  somewhat  rapidly,  it  is  bet- 
ter to  use  a  solution  of  iodine  in  potassium  iodide.  The  decom- 
position is  as  follows : 

HaS  +  21  =  2HI  +  S 

*  When  this  gas  remains  long  in  contact  with  mercury,  sulphide  of  mercury 
is  liable  to  be  formed.  f  Annal.  d.  Chem.  u.  Pharm.  162,  55. 


458  DETERMINATION.  [§  148. 

2  at.  I  =  253-70  correspond,  therefore,  to  1  mol.  HaS  =  34. 
However,  tins  exact  decomposition  can  be  relied  upon  with  cer- 
tainty only  if  the  amount  of  hydrogen  sulphide  in  the  fluid  does 
not  exceed  '04  per  cent.  (BUNSEN).  Fluids  containing  a  larger  pro- 
portion of  hydrogen  sulphide  must  therefore  first  be  diluted  to  the 
required  degree  with  boiled  wTater  cooled  out  of  the  contact  of  air. 

The  iodine  solution  of  §  146  may  be  used  for  the  estimation  of 
larger  quantities  of  hydrogen  sulphide ;  for  weak  solutions,  e.g., 
sulphuretted  mineral  water,  it  is  advisable  to  dilute  the  iodine  solu- 
tion 5  times,  so  that  1  c.c.  may  contain  -001  grm.  iodine. 

The  process  is  conducted  as  follows : 

Measure  or  weigh  a  certain  quantity  of  the  sulphuretted  water, 
dilute,  if  required,  in  the  manner  directed,  add  some  thin  starch- 
paste,  and  then  solution  of  iodine,  with  constant  shaking  or  stir- 
ring, until  the  permanent  blue  color  begins  to  appear.  The  result 
of  this  experiment  indicates  approximately,  but  not  with  positive 
accuracy,  the  relation  between  the  examined  water  and  the  iodine 
solution.  Suppose  you  have  consumed,  to  220  c.c.  of  the  sulphu- 
retted water,  12  c.c.  of  a  solution  of  iodine  containing  -000918 
grm.  iodine  in  the  c.c.*  Introduce  now  into  a  flask  nearly  the 
quantity  of  iodine  solution  required,  add  the  sulphuretted  water 
in  quantity  either  already  determined,  or  to  be  determined,  by 
weight  or  measure  ;f  then  to  the  colorless  fluid  add  thin  starch- 
paste,  and  after  this  iodine  solution  until  the  blue  color  just  begins 
to  show.  By  this  course  of  proceeding,  you  avoid  the  loss  of 
hydrogen  sulphide  which  would  otherwise  be  caused  by  evaporation 
and  oxidation.  In  my  analysis  of  the  Weilbach  water,  256  c.c.  of 
the  water  required,  in  my  second  experiment,  16-26  c.c.  of  iodine 
solution,  which,  calculated  to  the  quantity  of  sulphuretted  water 
used  in  the  first  experiment,  viz.,  220  c.c.,  makes  13-9  c.c.,  or  1*9 
c.c.  more.  But  even  now  the  experiment  cannot  yet  be  considered 
quite  conclusive,  when  made  with  a  solution  of  iodine  so  dilute ;  it 
being  still  necessary  to  ascertain  how  much  iodine  solution  is  required 
to  impart  the  same  blue  tint  to  the  same  quantity  of  ordinary  water 
mixed  with  starch-paste,  of  the  same  temperature,^:  and  as  nearly 
as  possible  in  the  same  condition  §  as  the  analyzed  sulphuretted 

*  The  numbers  here  stated  are  those  which  I  obtained  in  the  analysis  of  the 
Weilbach  water.  t  Compare  Experiment  No.  82. 

\  Annal.  d.  Chem.  u.  Pharm.  102,  186. 
§  In  this  connection  I  would  recommend,  in  cases  where  the  sulphuretted 


§  148.]  SULPHUR.  459 

water,  and  to  deduct  this  from  the  quantity  of  iodine  solution  used 
in  the  second  experiment.  Thus  in  the  case  mentioned,  I  had  to 
deduct  '5  c.c.  from  the  16'26  c.c.  used.  If  the  instructions  here 
given  are  strictly  followed,  this  method  gives  very  accurate  results. 

b.  Mix  the   sulphuretted  fluid  with  an  excess  of  solution  of 
sodium  arsenite,  add  hydrochloric  acid,  allow  to  deposit,  and  deter- 
mine the  arsenious  sulphide  as  directed  §  127,  4.     The  results  are 
accurate  unless  the  solution  is  very  dilute,  in  which  case  the  slight 
solubility  of  arsenious  sulphide  occasions  loss. 

c.  If  the  hydrogen  sulphide  is  evolved  in  the  gaseous  state,  and 
large  quantities  are  to  be  determined,  the  best  way  is  to  conduct  it 
first  through  several  bulbed  U-tubes  (fig.  64,  p.  435),  containing  an 
alkaline  solution  of  sodium  arsenite,  then  through  a  tube  connected 
with  the  exit  of  the  last  U-tube,  which  contains  pieces  of  glass 
moistened  with  solution  of  soda ;  to  mix  the  fluids  afterwards,  and 
proceed  as  in  b.     If,  on  the  other  hand,  we  have  to  determine 
small  quantities  of  hydrogen  sulphide  contained  in  a  large  amount 
of  air,  etc.,  it  is  well  to  pass  the  gaseous  mixture  in  separate  small 
bubbles  through  a  very  dilute  solution   of   iodine  in  potassium 
iodide,  of  known  volume  and  strength,  which  is  contained  in  a  long 
glass  tube  fixed  in  an  inclined  position  and  protected  against  sun- 
light.    The  free  iodine  remaining  is  finally  estimated  by  means 
of  a  solution  of  sodium  thiosulphate  (§  146) ;  the  difference  gives 
us  the  quantity  of  iodine  which  has  been  converted  by  hydrogen 
sulphide  into  hydriodic  acid,  and  consequently  corresponds  to  the 
amount  of  the  hydrogen  sulphide  present.     The  volume  of  the 
gaseous  mixture  may  be  known  by  measuring  the  water  which  has 
escaped  from  the  aspirator  used.     The  arrangement  of  the  absorp- 
tion tube  is  the  same  as  is  figured  in  connection  with  the  Deter- 
mination of  Carbonic  Acid  in  Air  (§  221).     The  thin  glass  tube  con- 
ducting the  gas  into  the  absorption  tube,  however,  must  not  be 
provided  with  an  india-rubber  elongation. 

From  my  own  experiments*  it  appears  that  sulphuretted 
hydrogen  whether  in  small  or  large  quantities  may  be  also  estimated 
by  the  increase  in  weight  of  absorption  tubes.  We  have  only  to 
take  care  that  the  mixture  of  gases  is  first  thoroughly  dried  by 
passing  over  calcium  chloride.  To  take  up  the  hydrogen  sulphide 

water  contains  bicarbonate  of  soda,  to  add  to  the  ordinary  water  an  equal  quan- 
tity of  this  salt,  as  its  presence  has  a  slight  influence  on  the  appearance  of  the 
final  reaction. 

*Zeitschr.  f.  anal.  Chem.  10,  75. 


460  DETERMINATION.  [§  148. 

we  use  U-tubes,  five  sixths  filled  with  copper  sulphate  on  pumice, 
one  sixth  at  the  exit  containing  calcium  chloride.  To  prepare  the 
pumice  with  copper  sulphate,  proceed  as  follows.  Treat  60  grm. 
pumice  in  lumps  the  size  of  peas  in  a  small  porcelain  dish  with  a 
hot  concentrated  solution  of  30  or  35  grm.  copper  sulphate,  dry 
the  whole  with  constant  stirring,  place  the  dish  in  an  air  or  oil 
hath  of  the  temperature  of  150°  to  160°,  and  allow  to  remain 
therein  four  hours.  A  tube  containing  14  grm.  of  this  prepared 
pumice  will  absorb  about  '2  grm.  hydrogen  sulphide.  It  is  wrell 
always  to  employ  two  such  tubes.  If  the  prepared  pumice  is  dried 
at  a  lower  temperature  it  takes  up  much  less  of  the  gas,  if  dried  at 
a  higher  temperature  the  gas  is  decomposed  and  sulphurous  acid  is 
formed. 

Finally,  small  quantities  of  hydrogen  sulphide  mixed  with  other 
gases  may  be  estimated  by  passing  through  bromine  water  and  con- 
verting into  sulphuric  acid. 

II.  Separation  and  Determination  of  Sulphur  in  Sulphides. 

A.   METHODS  BASED  ON  THE  CONVERSION  OF  THE  SULPHUR  INTO 

SULPHURIC  ACID. 

1.  Methods  in  the  Dry  Way. 

a.  Oxidation  ~by  Alkali  Nitrates  (applicable  to  all  compounds 
of  sulphur).  If  the  sulphides  do  not  lose  any  sulphur  on  heating, 
mix  the  pulverized  and  weighed  substance  with  6  parts  of  anhy- 
drous sodium  carbonate  and  4  of  potassium  nitrate,  with  the  aid 
of  a  rounded  glass  rod,  wipe  the  particles  of  the  mixture  which 
adhere  to  the  rod  carefully  off  against  some  sodium  carbonate,  and 
add  this  to  the  mixture.  Heat  in  a  platinum  or  porcelain  crucible 
(which,  however,  is  somewhat  affected  by  the  process),  at  a  grad- 
ually increased  temperature  to  fusion  ;*  keep  the  mass  in  that  state 
for  some  time,  then  allow  it  to  cool,  heat  the  residue  with  water, 
filter  the  fluid,  boil  the  residue  with  a  solution  of  pure  sodium  car- 
bonate, filter,  wash,  remove  all  nitric  acid  from  the  filtrate  by 
repeated  evaporation  with  pure  hydrochloric  acid,  and  determine 
the  sulphuric  acid  as  directed  in  §  132.  The  metal,  metallic  oxide, 
or  carbonate,  which  remains  undissolved,  is  determined,  according 
to  circumstances,  either  by  direct  weighing  or  in  some  other  suit- 
able way.  In  the  presence  of  lead,  before  filtering,  pass  carbonic 


*  If  gas  not  free  from  sulphur  is  used  for  heating,  some  sulphur  is  likely  to 
be  absorbed— PRICE,  Journ.  Chem.  Soc.,  (2)  2,  51.  If  a  platinum  crucible  is  used 
do  not  raise  the  heat  more  than  necessary,  or  Ihe  crucible  will  be  attacked. 


§  148.]  SULPHUR.  461 

acid  through  the  solution  of  the  fused  mass,  to  precipitate  the 
small  quantity  of  that  metal  which  has  passed  into  the  alkaline 
solution. 

Should  the  sulphides,  on  the  contrary,  lose  sulphur  on  heating, 
the  finely  powdered  compound  is  mixed  with  4  parts  sodium  car- 
bonate, 8  parts  nitre,  and  24  parts  pure  and  perfectly  dry  sodium 
chloride,  and  the  process  otherwise  conducted  as  already  given. 

b.  Oxidation  by  Chlorine  Gas  (after  BEEZELIUS  and  H.  ROSE 
especially  suitable  for  sulphosalts  of  complicated  composition). 

The  following  apparatus  (fig.  65),  or  one  of  similar  construction, 
is  used ;  corks  should  be  used,  not  india-rubber  stoppers,  and  wher- 
ever there  is  an  india-rubber  connection,  the  glass  tubes  should  be 
close  to  each  other. 

The  flask  a  is  completely  filled  with  pieces  of  pyrolusite  (native 
manganese  dioxide)  of  the  size  of  hazelnuts,  strong  hydrochloric 
acid  is  poured  in  till  the  spaces  between  the  pieces  of  pyrolusite 
are  filled  up  to  half  the  height  of  the  body  of  the  flask.  The 
upper  layer  of  pyrolusite,  which  should  be  rinsed  with  a  little  water 
after  pouring  in  the  hydrochloric  acid,  serves  to  purify  the  evolved 
chlorine  almost  completely  from  hydrochloric  acid.  When  the 
stopcock  in  one  of  the  tubes  provided  for  conducting  the  chlorine  is 
closed,  the  chlorine  passes  down  into  the  cylinder  b  filled  with 
rather  dilute  soda  solution,  by  which  it  is  completely  absorbed. 
When  the  stopcock  is  opened  the  chlorine  is  conducted  by  a  tube 
to  the  bottom  of  c  into  a  layer  of  concentrated  sulphuric  acid,  which 
serves  to  indicate  the  rapidity  of  the  current ;  c  is  moreover  com- 
pletely filled  with  fragments  of  pumice-stone  moistened  with  con- 
centrated sulphuric  acid,  for  the  purpose  of  drying  the  chlorine. 
The  tube  with  the  bulb  d  must  be  made  of  glass  which  is  not  too 
easily  fusible,  and  must  be  adjusted,  not  horizontally,  but  a  little 
inclined,  so  that  heavy  vapors  may  not  pass  back  against  the  slow 
current  of  chlorine.  The  danger  that  vapors  may  pass  back  is 
further  lessened  by  making  the  end  of  the  bulb-tube  at  which 
chlorine  enters  no  wider  than  is  necessary  for  the  introduction  of 
the  substance  by  means  of  a  long,  narrow,  thin  weighing  tube.  The 
part  of  the  tube  on  the  other  side  of  the  bulb  should  have  a  greater 
diameter,  since  it  might  otherwise  be  choked  up  by  a  sublimate, 


462 


DETERMINATION. 


[§148. 


especially  if  the  substance  contains  much  antimony.  It  is  narrowed 
at  one  point  to  facilitate  subsequent  fusion  and  drawing  asunder. 
The  downward  bent  end  is  fitted  into  the  receiver  e  by  means  of  a 
cork,  or  a  piece  of  rubber  tubing  drawn  over  it.  The  receiver  con- 
tains water  or,  if  antimony  is  present  in  the  substance,  dilute  hydro- 
chloric acid  to  which  is  also  added  a  little  tartaric  acid  (free  from 
sulphuric  acid).  The  volume  of  liquid  should  be  only  so  large  as  to 
cause  the  passing  gas  to  bubble  through  it  in  the  narrow  spaces  at 
each  end  of  the  lower  bulb,  which  should  be  large  enough  to  hold  25 


Fig.  65 

to  30  c.c.  when  thus  charged.  It  is  well  also  to  attach  to  the  receiver 
a  small  U-tube  charged  with  a  small  volume  of  the  liquid  absorbent 
in  such  a  manner  as  to  increase  as  little  as  possible  the  pressure  in 
the  interior  of  the  apparatus.  Finally,  a  long,  light  glass  tube  may  be 
attached  to  the  last  U-tube  for  conducting  the  escaping  chlorine 
into  the  open  air  or  into  a  flue. 

When  the  substance  has  been  introduced  into  the  bulb-tube,  and 
the  whole  apparatus  is  connected,  the  stopcock  is  first  closed  and 


§  148.]  SULPHUR.  463 

evolution  of  chlorine  is  produced  by  application  of  gentle  heat. 
A  B  soon  as  gas-bubbles  following  each  other  in  quick  succession 
appear  in  the  soda  solution,  the  heat  is  withdrawn.  A  constant 
evolution  of  chlorine  will  then  go  on  for  a  long  time  without  fur- 
ther application  of  heat.  "When  the  gas-bubbles  are  nearly  com- 
pletely absorbed  by  the  soda  solution,  the  stopcock  is  opened  so 
wide  that  a  slow  current  of  gas  enters  c  and  after  a  while  reaches 
the  bulb  d.  If  the  substance  is  decomposed  at  the  ordinary  tem- 
perature (e.g.,  antimony  sulphide),  care  must  be  taken  to  diminish 
the  rapidity  of  the  chemical  action  and  consequent  elevation  of 
temperature,  by  partial  closing  of  the  stopcock,  so  that  sulphur 
chloride  may  not  distil  over  into  the  receiver  at  this  stage  of  the 
process.  For  if  sulphur  chloride  reaches  the  liquid  in  the  receiver 
which  is  not  yet  saturated  with  chlorine,  it  is  decomposed  with 
separation  of  sulphur  which  is  afterwards  not  easily  converted  into 
sulphuric  acid  by  chlorine.  "When  the  action  of  chlorine  ceases  to 
produce  elevation  of  temperature  or  any  apparent  change  of  the 
substance,  and  the  absorbing  liquid  has  become  charged  with 
chlorine,  the  current  is  slightly  increased  and  gentle,  very  gradu- 
ally increased  heat  is  applied  to  the  bulb,  which,  however,  is  not 
even  at  the  end  of  the  operation  brought  to  redness.  During  this 
operation  the  flow  of  chlorine  must  not  be  so  rapid  as  to  carry 
visible  fumes  through  the  absorbing  apparatus,  and  sulphur  chloride 
must  be  distilled  over  so  slowly  that  the  absorbing  liquid  remains 
throughout  well  charged  with  chlorine.  If  the  latter  precaution, 
is  neglected,  unoxidized  sulphur  will  remain  at  the  close  of  the 
operation,  which  will  render  the  subsequent  part  of  the  process 
more  troublesome  and  probably  less  accurate.  Besides  sulphur 
chloride,  the  volatile  metallic  chlorides  distil  over.  The  portion 
of  the  tube  beyond  the  bulb  may  be  kept  moderately  heated  so  as 
to  prevent  it  from  being  stopped  up  by  a  sublimate,  especially  at 
the  narrowed  part.  When  by  gradually  increased  temperature  no 
more  volatile  products  arise  from  the  mass  in  the  bulb  and  con- 
dense in  the  cooler  portion  of  the  tube  beyond  it,  except  perhaps 
ferric  chloride  (giving  a  dark  brown  sublimate),  the  complete 
expulsion  of  which  need  not  be  awaited,  the  heating  is  extended 
so  that  the  sublimate  in  the  tube  is  gradually  driven  as  far  as  prac- 
ticable into  the  receiver,  or  at  least  beyond  the  narrowed  part. 
The  stopcock  is  then  closed  while  the  bulb  is  still  warm.  "When, 
after  a  few  minutes,  the  liquid  in  the  receiver  has  receded  some- 


464  DETEKMINATION.  [§  148. 

what,  soften  the  narrow  part  of  the  tube  with  the  flame  of  a  Bnnsen 
burner  aided  by  a  blowpipe  having  a  rather  large  jet,  and  at  the 
same  time  draw  the  tube  asunder. 

The  drawn-off  end  of  the  tube  containing  anhydrous  chlorides, 
which  volatilize  on  exposure  to  the  air,  must  not  be  withdrawn 
from  the  receiver  until  the  chlorides  are  dissolved  or  have  by  long 
standing  absorbed  moisture.  Their  solution  is  easily  effected  pro- 
vided the  tube  extends  well  down  into  the  receiver  by  inclining 
the  latter  so  that  liquid  comes  in  contact  with  the  end  of  the  tube. 
The  liquid  then  gradually  rises  in  the  tube,  absorbing  the  chlorine 
gas  and  dissolving  the  chlorides  in  it ;  meantime,  if  necessary,  the 
cork  may  be  slightly  loosened  to  admit  a  little  air  and  prevent  the 
liquid  from  reaching  it  by  absorption  of  chlorine.  If  one  fails  to 
effect  a  solution  in  the  manner  above  described,  the  whole  may  be 
allowed  to  stand  24  hours,  during  which  time  the  chlorides  in  the 
tube  absorb  moisture  from  the  liquid  in  the  receiver,  so  that  the 
tube  can  then  be  withdrawn  and  the  chlorides  may  be  dissolved 
out  with  diluted  hydrochloric  acid  and  added  with  rinsings  of  the 
tube  to  the  solution  in  the  receiver.  Finally,  if  it  is  intended  to 
adopt  this  latter  mode  of  proceeding,  the  tube  may  be  cut  off  and 
immediately  closed  with  a  cork  instead  of  being  fused  and  drawn 
off.  The  solution  of  the  chlorides  obtained  from  the  end  of  the 
tube,  the  solution  in  the  receiver  and  that  in  the  appended  U-tube 
being  united,  a  very  gentle  heat  is  applied  until  the  free  chlorine  is 
expelled,  and  the  fluid  is  then  allowed  to  stand  until  the  sulphur, 
if  any  is  present,  has  solidified.  The  sulphur  is  filtered  off  on  a 
weighed  filter,  washed,  dried,  and  weighed.  The  filtrate  is  precipi- 
tated with  barium  chloride  (§132),  by  which  operation  the  amount 
of  that  portion  of  the  sulphur  is  determined  which  has  been  con- 
verted into  sulphuric  acid.  The  fluid  filtered  from  the  barium  sul- 
phate contains,  besides  the  excess  of  barium  chloride  added,  also 
the  volatile  metallic  chlorides ;  which  latter  are  finally  determined 
in  it  by  the  proper  methods,  which  will  be  found  in  Section  Y. 

The  chloride  remaining  in  the  bulb-tube  is  either  at  once 
weighed  as  such  (silver  chloride,  lead  chloride),  or  where  this  is 
impracticable — as  in  the  case  of  copper,  for  instance,  which  remains 
partly  as  cuprous,  partly  as  cupric  chloride — it  is  dissolved  in  water, 
hydrochloric  acid,  nitrohydrochloric  acid,  or  some  other  suitable 
solvent,  and  the  metal  or  metals  in  the  solution  are  determined  by 
the  methods  already  described,  or  which  will  be  found  in  Section 


§  148.]  SULPHUR.  465 

Y.  To  be  enabled  to  ascertain  the  weight  of  the  bulb-tube  con- 
taining silver  chloride,  it  is  advisable  to  reduce  the  chloride  by 
hydrogen  gas,  and  then  dissolve  the  metal  in  nitric  acid. 

In  cases  where  you  have  only  to  estimate  the  sulphur,  say  in 
substances  containing  also  sulphuric  acid,  O.  LLNDT*  recommends 
conducting  the  chloride  of  sulphur  and  the  volatile  metallic 
chlorides  into  pure  solution  of  soda,  when  decomposition  immedi- 
ately takes  place,  producing  sodium  sulphide,  sodium  thiosulphate, 
sodium  chloride,  and  hypochlorite.  When  the  decomposition  is 
over,  continue  passing  the  chlorine  for  two  hours  through  the  soda, 
evaporate  then  to  dryness,  ignite  the  residue  cautiously  to  destroy 
the  sodium  chlorate,  dissolve  in  water,  and  estimate  the  sulphuric 
acid  according  to  §  132. 

c.   Oxidation  ~by  Oxide  of  Mercury  (after  BUNSEN). 

This  method,  which  will  be  found  in  detail,  §  186,  is  particu- 
larly suited  to  the  estimation  of  sulphur  in  volatile  compounds,  or 
in  substances  which  when  heated  lose  sulphur. 

2.  Methods  in  the  Wet  Way. 

a.  Oxidation  of  the  Sulphur  by  Acids  yielding  Oxygen,  or  ~by 
Halogens. f 

a.  Weigh  the  finely  pulverized  sulphide  in  a  small  glass  tube 
sealed  at  one  end,  and  drop  the  tube  into  a  tolerably  capacious 
strong  bottle  with  glass  stopper,  which  contains  red  fuming  nitric 
acid  (perfectly  free  from  sulphuric  acidj)  in  more  than  sufficient 
quantity  to  effect  the  decomposition  of  the  sulphide.  Immediately 
after  having  dropped  in  the  tube,  close  the  bottle.  When  the  action, 
which  is  very  impetuous  at  first,  has  somewhat  abated,  shake  the 
bottle  a  little ;  as  soon  as  this  operation  ceases  to  cause  renewed 
action,  and  the  fumes  in  the  flask  have  condensed,  take  out  the 
stopper,  rinse  this  with  a  little  nitric  acid  into  the  bottle,  and  then 
heat  the  latter  gently. 

aa.  The  whole  of  the  Sulphur  has  been  oxidized,  the  Fluid  is 


*  Zeitschr.  f.  anal.  Chem.  4,  370. 

f  In  presence  of  lead,  barium,  strontium,  calcium,  tin,  and  antimony,  method 
b  is  preferable  to  a. 

$  To  test  for  sulphuric  acid  in  nitric  or  hydrochloric  acid,  it  is  necessary  to 
evaporate  on  a  water-bath  nearly  to  dryness  and  take  up  with  water  before  add- 
ing barium  chloride.  When  the  acid  cannot  be  got  pure,  determine  the  sulphuric 
acid  and  allow  for  it. 


466  DETERMINATION.  [§  148. 

perfectly  clear  :*  Evaporate  with  some  sodium  chloride,  towards 
the  end  adding  pure  hydrochloric  acid  repeatedly,  cooling  the  dish 
each  time  before  adding  the  acid.  Dilute  with  much  water,  and 
determine  the  sulphuric  acid  as  directed  §  132.  Make  sure  that  the 
pre'cipitate  is  pure  ;  if  it  is  not,  purify  it  according  to  §  132.  Separate 
the  bases  in  the  filtrate  from  the  excess  of  the  barium  salt  by  the 
methods  given  in  Section  Y. 

l)b .  Undissolved  Sulphur  floats  in  the  Fluid:  Add  potassium 
chlorate  in  small  portions,  or  strong  hydrochloric  acid,  and  digest 
some  time  on  a  water-bath.  This  process  will  often  succeed  in  dis- 
solving the  whole  of  the  sulphur.  Should  this  not  be  the  case,  and 
the  undissolved  sulphur  appear  of  a  pure  yellow  color,  dilute  with 
water,  collect  on  a  weighed  filter,  wash  carefully,  dry,  and  weigh. 
After  weighing,  ignite  the  whole,  or  a  portion  of  it,  to  ascertain 
whether  it  is  perfectly  pure.  If  a  fixed  residue  remains  (consisting 
commonly  of  quartz,  gangue,  &c.,  but  possibly  also  of  lead  sul- 
phate, barium  sulphate,  &c.),  deduct  its  weight  from  that  of  the 
impure  sulphur.  In  the  filtered  fluid  determine  the  sulphuric  acid 
as  in  aa,  calculate  the  sulphur  in  it,  and  add  the  amount  to  that  of 
the  undissolved  sulphur.  If  the  residue  left  upon  the  ignition  of 
the  undissolved  sulphur  contains  an  insoluble  sulphate,  decompose 
this  as  directed  in  §  132,  and  add  the  sulphur  found  in  it  to  the 
principal  amount. 

In  the  presence  of  bismuth,  the  addition  of  potassium  chlorate 
or  of  hydrochloric  acid,  is  not  advisable,  as  chlorine  interferes  with 
the  determination  of  bismuth. 

/?.  Mix  the  finely  pulverized  metallic  sulphide  in  a  dry  flask, 
by  shaking,  with  powdered  potassium  chlorate  (free  from  sulphuric 
acid),  and  add  moderately  concentrated  hydrochloric  acid  in  small 
portions.  Cover  the  flask  with  a  watch-glass,  or  with  an  inverted 
small  flask.  After  digestion  in  the  cold  for  some  time,  heat  gently, 
finally  on  the  water-bath,  until  the  fluid  smells  no  longer  of  chlo- 
rine. Proceed  now  as  directed  in  a,  aa,  or  £J,  according  as  the 
sulphur  is  completely  dissolved  or  not.  In  the  latter  case  you  must 
of  course  immediately  dilute  and  filter.  The  oxidation  of  the  sul- 
phur may  be  usually  effected  more  quickly  and  completely  by 

*  This  can  of  course  be  the  case  only  in  absence  of  metals  forming  insoluble 
salts  with  sulphuric  acid.  If  such  metals  are  present,  proceed  as  in  bb,  as  it  is  in 
that  case  less  easy  to  judge  whether  complete  oxidation  of  the  sulphur  has  beer 
attained. 


§  148.]  SULPHUR.  467 

warming  with  nitric  acid  of  1*36  sp.  gr.  on  a  water-bath,  and  add- 
ing potassium  chlorate  in  small  portions.  Compare  STOKER,*  PEAR- 
SOX,  and  BowDiTCH.f 

y.  Aqua  regia  is  also  frequently  used.  J.  LEFORT^:  recommends 
a  mixture  of  1  part  strong  hydrochloric  acid  and  3  parts  strongest 
nitric  acid.  Complete  conversion  of  sulphur  into  sulphuric  acid, 
however,  is  rarely  effected  by  aqua  regia. 

6".  Bromine  may  also  be  used.  Pyrites  or  blende  is  digested  at 
a  gentle  heat  with  water,  and  bromine  gradually  added.  If  the  sul- 
phides have  been  prepared  in  the  wet  way,  good  bromine  water  is 
sufficient  to  oxidize  them.  P.  WAAGE§  prefers  bromine  to  all  other 
wet  agents,  and  advises  its  purification  by  distillation  in  an  appa- 
ratus from  which  all  caoutchouc  connections  are  excluded. 

J).  Oxidation  of  the  Sulphur  by  Chlorine  in  Alkaline  Solution, 
after  RIVOT,  BEUDANT,  and  DAGUIN.||  (Suitable  also  for  determining 
the  sulphur  in  the  crude  article.) 

Heat  the  very  finely  pulverized  sulphide  or  crude  sulphur  for 
several  hours  with  solution  of  potassa  free  from  sulphuric  acid 
(which  dissolves  free  sulphur,  as  well  as  the  sulphides  of  arsenic 
and  antimony),  and  then  conduct  chlorine  into  the  fluid.  This 
speedily  oxidizes  the  sulphur ;  the  sulphuric  acid  formed  combines 
with  the  potassa  to  sulphate,  which  dissolves  in  the  fluid,  whilst 
the  metals  converted  into  oxides  remain  undissolved.  Filter,  acid- 
ify the  alkaline  filtrate,  and  precipitate  the  sulphuric  acid  by  barium 
chloride  (§  132).  Arsenic  and  antimony  pass  into  the  alkaline 
solution  in  the  form  of  acids,  but  not  so  lead,  which  is  converted 
into  binoxide,  and  remains  completely  undissolved.  This  method 
is,  therefore,  particularly  suitable  in  presence  of  lead  sulphide.  In 
presence  of  iron  sulphide,  potassium  sulphate  is  formed  at  first, 
and  ferric  hydroxide,  which,  if  the  action  of  the  chlorine  is  allowed 
to  continue,  begins  to  be  converted  into  potassium  ferrate.  As 
soon,  therefore,  as  the  fluid  commences  to  acquire  a  red  tint  the 
transmission  of  chlorine  must  be  discontinued,  and  the  fluid  gently 
heated  for  a  few  moments  with  powdered  quartz,  to  decompose  the 
ferric  acid. 

It  occasionally  happens,  more  particularly  in  presence  of  sand, 
iron  pyrites,  cupric  oxide,  &c.,  that  the  process  is  attended  with 
impetuous  disengagement  of  oxygen,  which  almost  completely  pre- 

*  Zeitschr.  f.  anal.  Chem.  9,  71.  f  Ib.  9,  82.  J  Ib.  9,  81. 

§  Ib.  10,  206.        ||  Compt.  Rend.  1835,  865  ;  Journ.  f.  prakt.  Chem.  61,  134. 


468  DETERMINATION.  [§  148. 

vents  the  oxidizing  action  of  the  chlorine.  However,  this  accident 
may  be  guarded  against  by  reducing  the  substance  to  the  very  finest 
powder. 

J2.  METHODS  BASED  ON    THE    CONVERSION  OF  THE  SULPHUR  INTO 
HYDROGEN  SULPHIDE,  OK  A  METALLIC  SULPHIDE. 

a.  The  determination  of  the  sulphur  in  the  sulphides  of  the 
metals  of  the  alkalies  and  alkaline  earths  soluble  in  water  is  best 
effected — provided  they  are  free  from  excess  of  sulphur — by  L,  l>. 
In  the  absence  of  acids  of  sulphur  you  may  also  convert  the  sulphur 
into  sulphuric  acid  by  bromine  water.     The  bases  are  conveniently 
estimated  in  a  separate  portion,  which  is  decomposed  by  evapora- 
tion with  hydrochloric  or  sulphuric  acid,  or — when  none  but  alkali- 
metals  are  present — by  ignition  with  5  parts  of  ammonium  chloride 
in  a  porcelain  crucible.     If  the  compounds  contain  excess  of  sul- 
phur, they  should  be  oxidized  either  by  chlorine  in  alkaline  solu- 
tion or  treated  according  to  B,  c ;  if  they  contain  thiosulphate  or 
sulphite,  proceed  according  to  §  168. 

b.  The  sulphur  contained  in  alkaline  fluids  as  monosulphide  or 
Iiydrosulphate  of  the  sulphide  may  also  be  determined  directly  by 
volumetric  analysis,  by  means  of  a  standard  ammoniacal  silver  or 
copper  solution.  In  using  the  former,  mix  the  solution  with  ammo- 
nia, heat  and  add  the  standard  fluid  till,  on  filtering  off  a  small 
portion  and  adding  silver  solution,  a  mere  opalescence  is  produced 
(LESTELLE*).     In  using  the  copper  solution,  mix  the  fluid  to  be 
tested  with  ammonia,  heat  to  50°  or  60°,  and  add  the  standard  solu- 
tion, frequently  shaking  and  boiling  till  no  further  precipitation  of 
CuO,  5CuS  is  produced,  and  the  solution  begins  to  be  blue  (VER- 
STRAETf).     To  make  a  standard  copper  solution,  1  c.c.  of  which 
shall  equal  .01,  E"a2S,  dissolve  9.754  pure  copper  in  40  grm.  nitric 
acid,  boil,  add  180  to  200  c.c.  ammonia  and  water  to  1  litre.  These 
methods  are  well  adapted  for  technical  purposes,  for  the  estimation 
of  sulphide  in  soda  lies  for  instance.    It  need  hardly  be  added  that 
precipitated  silver,  copper,  or  lead  sulphide  (if  you  have  used  a 
solution  of  oxide  of  lead  in  potash)  may  be  estimated  gravimetri- 
cally. 

c.  If  all  the   sulphur  can  be  expelled  from  the  substance  in  the 
form  of  sulphuretted  hydrogen  by  heating  with  hydrochloric  acid, 
the  sulphide  may  be  heated  in  a  small  flask  with  the  concentrated 

*  Zeitschr.  f.  anal.  Chem.  2,  94.  f  Ib.  4,  216. 


g  149.]  NITRIC   ACID.  46t> 

acid  to  complete  decomposition  and  expulsion  of  the  hydrogen  sul- 
phide —  the  latter  being  determined  according  to  I.  In  the  case  of 
polysulphides,  the  sulphur  separated  in  the  evolution  flask  is  col- 
lected on  a  filter  dried  at  100°,  washed,  dried  first  at  70°,  then  for 
a  short  time  at  100°,  and  weighed. 

Third  Group. 

NITKIC    ACID.  -  CHLORIC    ACID. 


1.  XITKIC  ACID.  . 

I.  Determination. 

Free  nitric  acid  in  a  solution  containing  no  other  acid  is  deter- 
mined most  simply  in  the  volumetric  way,  by  neutralizing  with  a 
dilute  solution  of  soda  or  ammonia  of  known  strength  (comp.  Spe- 
cial Part,  "  Acidimetry").  The  following  method  also  effects  the 
same  purpose  :  Mix  the  solution  with  baryta-water,  until  the  reac-  * 
tion  is  just  alkaline,  evaporate  slowly  in  the  air,  nearly  to  dryness, 
dilute  the  residue  with  water,  filter  the  solution  which  has  ceased 
to  be  alkaline,  wash  the  barium  carbonate  formed  by  the  action  of 
the  carbonic  acid  of  the  atmosphere  upon  the  excess  of  the  baryta- 
water,  add  the  washings  to  the  filtrate,  and  determine  in  the  fluid 
the  barium  as  directed  in  §  101.  Calculate  for  each  1  at.  barium 
2  mol.  nitric  acid.  Lastly,  free  nitric  acid  may  also  be  determined 
in  a  simple  manner  by  supersaturating  with  ammonia,  evaporating 
in  a  weighed  platinum  dish,  drying  the  residue  at  110°  to  120°, 
and  weighing  the  NH4NO3  (SCHAFFGOTSCII): 

II.  Separation  of  nitric  add  from  the  basic  radicals,  and 

determination  of  the  acid  in  nitrates. 

a.  Methods  based  on  the  decomposition  of  Nitrates  in  the  Dry 
Way. 

ex.  In  anhydrous  metallic  nitrates  which  leave  upon  ignition  a 
metallic  oxide  of  known  and  definite  composition,  the  nitric  acid 
may  be  determined  by  ignition  and  calculation  from  the  weight  of 
the  residue. 

ft.  In  the  case  of  nitrates,  whose  residue  on  ignition  has  no 
constant  composition,  or  by  whose  ignition  the  crucible  is  much 
attacked  (alkali  and  alkali-earth  nitrates),  fuse  the  substance  (which 


470  DETERMINATION.  [§  149. 

must  be  anhydrous  and  also  free  from  organic  and  other  volatile 
bodies)  with  a  noil- volatile  flux,  and  estimate  the  nitric  acid  from 
the  loss.  Silicic  acid  is  the  best  flux,  as  it  may  be  readily  procured, 
and  the  execution  is  the  most  easy  and  the  most  certain  to  succeed. 
I  shall  describe  the  method  in  its  application  to  potassium  or  sodium 
nitrate. 

Fuse  the  latter  at  a  low  temperature,  pour  out  on  to  a  warm 
porcelain  dish,  powder,  and  dry  again  before  weighing..  Now 
transfer  to  a  platinum  crucible  2  to  3  grin,  powdered  quartz,  ignite 
well,  and  weigh  after  cooling.  Add  about  0*5  grm.  of  the  salt 
prepared  as  above,  mix  well,  and  convince  yourself  by  the  balance 
that  nothing  has  been  lost  during  mixing.  The  covered  crucible 
is  then  exposed  to  a  low  "red  heat  (just  visible  by  day)  for  half  an 
hour,  and  weighed  after  cooling  with  the  cover.  The  loss  of 
weight  represents  the  quantity  of  K9OS.  Sulphates  or  chlorides 
are  not  decomposed  at  the  given  temperature  ;  if  a  higher  heat  be 
applied,  the  latter  may  volatilize.  The  action  of  reducing  gases 
must  be  avoided.  The  test-analyses,  communicated  by  REICH,*  as 
well  as  those  performed  in  my  own  laboratory,  f  gave  very  satisfac- 
tory results. 

I).  Method  based  on  tJie  distillation  of  Nitric  Acid. 

All  nitrates  may  be  decomposed  by  distillation  with  moderately 
dilute  sulphuric  acid.  The  nitric  acid  passing  into  the  receiver 
may  then  be  determined,  according  to  L,  volumetrically  or  gravi- 
metrically.  1  to  2  grm.  of  the  nitrate  should  be  treated  with  a 
cooled  mixture  of  1  volume  concentrated  sulphuric  acid  and  2  vol- 
umes water.  For  1  grm.  nitre  take  5  c.c.  sulphuric  acid  and  10 
c.c.  water.  The  distillation  may  be  performed  either  with  a  ther- 
mometer at  160°  to  170°  in  a  paraffin  or  sand  bath  (duration  of  the 
distillation  for  1  to  2  grm.  nitre,  3  to  4  hours),  or  in  vacuo,  with 
the  use  of  a  water-bath.  The  latter  process  is  the  best.  In  the 
former,  the  neck  of  the  tubulated  retort  (which  is  drawn  out  and 
bent  down)  is  connected  with  a  bulbed  TJ-tubeJ  containing  a  meas- 
ured quantity  of  standard  soda  or  potassa  solution  (§  192).  The 
distillation  in  vacuo  may  be  conducted,  without  the  use  of  an  air- 
pump,  according  to  FINKENER,||  as  follows:  Transfer  the  measured 

*  Berg-  und  Huttenmannische  Zeitschrift,  1861,  No.  21;  Zeitschrifl  f.  analyt. 
Chem.  1,  86.  t  Zeitschr.  f.  anal.  Chem,  1,  181. 

\  The  bulbed  U-tube  will  be  found  figured  §  185. 
||  Zeitschrift  f.  analyt.  Chem.  1,  309. 


§  149.]  NITRIC    ACID.  471 

quantity  of  water  and  concentrated  sulphuric  acid  to  the  tubulated 
retort,  and  the  necessary  quantity  of  standard  potassa  or  soda  solu- 
tion, diluted  to  30  c.c.,  to  a  flask  with  a  narrow  neck  of  about  200 
c.c.  capacity.  Then,  by  means  of  an  india-rubber  tube,  connect  the 
flask  with  the  retort  air-tight,  so  that  the  drawn-out  point  of  the 
latter  may  extend  to  the  body  of  the  flask,  and — with  tubulure 
open — heat  the  contents  of  the  retort  and  of  the  flask  to  boiling. 
When  the  air  has  been  expelled  from  the  apparatus  by  long  boil- 
ing, transfer  the  salt  (weighed  in  a  small  tube)  to  the  retort  through 
the  tubulure,  close  the  latter  immediately,  and  at  the  same  time 
take  away  the  lamp.  The  retort  is  then  heated  with  a  water-bath, 
the  flask  being  kept  cool.  The  quantity  of  nitric  acid  that  has 
passed  over  is  finally  ascertained  by  determining  the  still  free  alkali 
with  standard  acid.  If  it  is  suspected  that  all  the  nitric  acid  has 
not  been  driven  into  the  receiver  by  one  distillation,  you  may — by 
heating  the  flask  and  cooling  the  retort — distil  the  water  back  into 
the  latter,  and  then  the  distillation  from  the  retort  may  be  repeated. 
The  distillate  thus  obtained  is  always  free  from  sulphuric  acid,, 
hence  the  results  are  very  exact.  The  base  remains  as  sulphate  in* 
the  retort.  In  the  presence  of  chloride  add  to  the  contents  of  the 
retort  a  sufficiency  of  dissolved  silver  sulphate,  or — when  much 
chloride  is  present — moist  silver  oxide.  The  nitric  acid  is  then 
obtained  entirely  free  from  chlorine. 

c.  Methods  based  on  the  decomposition  of*  Nitrates  by  Alka- 
lies,  &c. 

a.  jSTitrates  of  metals  which  are  completely  precipitated  by 
alkali  hydroxides  or  carbonates — provided  basic  salts  are  not  pre- 
cipitated at  the  same  time — may  be  analyzed  by  simple  boiling 
with  an  excess  of  standard  potassa  or  soda  or  their  carbonates. 
After  cooling,  dilute  to  J  or  ^  litre,  mix,  allow  to  settle,  draw  off  a 
portion  of  the  supernatant  clear  fluid,  determine  the  free  alkali 
remaining  in  it,  and  calculate  therefrom  the  amount  which  has 
been  converted  into  nitrate.  HAYES  obtained  with  silver  and  bis- 
muth nitrates  good  results;  but  with  mercurous  nitrate  (using 
sodium  carbonate)  the  results  were  not  so  satisfactory.* 

/?.  In  nitrates  from  which  the  basic  metals  are  precipitated  by 
barium  or  calcium  hydroxides  or  their  carbonates  (or  by  barium 
sulphide),  the  nitric  acid  may  be  estimated  with  great  accuracy  by 

*  H.  Rose,  Zeitschrift  f.  analyt.  Chem.  1,  306. 


472  DETERMINATION.  [§  149. 

filtering,  after  precipitation  lias  been  effected,  warm  or  cold,  pass- 
ing carbonic  acid  through  the  filtrate,  if  necessary,  till  all  the 
barium  is  precipitated,  warming,  filtering,  and  determining  the 
barium  in  the  filtrate  by  sulphuric  acid.  1  at.  of  the  same  corre- 
sponds to  1  mol.  nitric  anhydride  (N~aO6).  [In  case  of  bismuth- 
salts,  boil  until  the  separated  oxide  is  perfectly  yellow.  PAIGE.] 

y.  In  many  nitrates  whose  bases  are  precipitable  by  sulphuret- 
ted hydrogen  the  nitric  acid  may  be  determined  according  to  GIBB& 
by  adding  to  the  salt  in  solution  about  its  own  weight  of  some 
neutral  organic  salt,  e.g.,  Rochelle  salt,  and  throwing  down  the 
metal  by  H2S.  The  filtrate  and  wrashings  are  brought  to  a  definite 
bulk,  and  the  free  acid  is  determined  in  aliquot  portions  alkalimet- 
rically.* 

d.  Methods  based  upon  the  decomposition  of  Nitric  Acid  by 
Ferrous  Chloride. 

Method  of  PELouzEf  and  FRESENIUS.  The  decompositio  n  is  a 
follows : 

6FeCl2  +  2KN03  +  8HC1  =  3Fe2Cl6  +  2KC1  +  4H2O  +  N.O,- 

a.  Select  a  tubulated  retort  of  about  200  c.c.  capacity,  with  a 
long  neck,  and  fix  it  so  that  the  latter  is  inclined  a  little  upwards. 
Introduce  into  the  body  of  the  retort  about  1-5  grin,  fine  piano- 
forte wire,  accurately  weighed,  and  add  about  30  or  40  c.c.  pure 
fuming  hydrochloric  acid.  Conduct  now  through  the  tubulure,  by 
means  of  a  glass  tube  reaching  only  about  2  cm.  into  the  retort,, 
hydrogen  gas  washed  by  solution  of  potassa,  or  pure  carbonic  acid,, 
and  connect  the  neck  of  the  retort  with  a  U-tube  containing  some 
water.  Place  the  body  of  the  retort  on  a  water-bath,  and  heat 
gently  until  the  iron  is  dissolved.  Let  the  contents  of  the  retort 
cool  in  the  current  of  hydrogen  gas  or  carbonic  acid ;  increase  the 
latter,  and  drop  in,  through  the  neck  of  the  retort,  into  the  body, 
a  small  tube  containing  a  weighed  portion  of  the  nitrate  under 
examination,  which  should  not  contain  more  than  about  0*200  grin, 
of  N2O5.  After  restoring  the  connection  between  the  neck  and 
the  U-tube,  heat  the  contents  of  the  retort  in  the  water-bath  for 
about  a  quarter  of  an  hour,  then  remove  the  water-bath,  heat  with 
the  lamp  to  boiling,  until  the  fluid,  to  which  the  nitric  oxide  had 
imparted  a  dark  tint,  shows  the  color  of  ferric  chloride,  and  con- 

*  Am.  Jour..Sci.,  xliv.  209.  \  Journ.  f.  prakt.  Chem.  40,  324. 


£  149.]  MTKIC   ACID.  473 

tinue  boiling  for  some  minutes  longer.  Care  must  be  taken  to 
give  the  fluid  an  occasional  shake,  to  prevent  the  deposition  of  dry 
salt  on  the  sides  of  the  retort.  Before  you  discontinue  boiling, 
increase  the  current  of  hydrogen  or  carbonic  acid  gas,  that  no  air 
may  enter  through  the  U-tube  when  the  lamp  is  removed.  Let 
the  contents  cool  in  the  current  of  gas,  dilute  copiously  with  water, 
and  determine  the  iron  still  present  as  ferrous  chloride  volumetri- 
cally  by  potassium  dichromate — 336  of  iron  converted  by  the 
nitric  acid  from  ferrous  to  ferric  chloride  correspond  to  108  (KaO6). 
My  test-analyses  of  pure  potassium  nitrate  gave  100*1 — 100*03 — 
100*03,  and  100*05,  instead  of  100.*  [The  iron  remaining  as  ferric 
chloride  may  also  be  determined  by  sodium  thiosulphate.] 
ft.  SCHULZE'S  Methodf  modified  by  TIEMANN.^ 

The  solution  containing  the  nitrate  is  concentrated  if  necessary 
to  a  volume  of  about  50  c.c.  and  introduced  into  the  flask  A,  which 
should  have  a  capacity  of  about  200  c.c.  This  flask  is  provided 
with  a  rubber  stopper,  through  which  pass  two  bent  tubes  a  b  c  and 
ef  g.  The  first  is  drawn  out  to  a  point  (not  too  small)  at  a,  and 
projects  through  the  stopper  about  2  cm. ;  the  second  terminates 
without  diminution  of  size  exactly  at  the  lower  surface  of  the 
stopper.  These  two  tubes  are  connected  by  rubber  tubes  (bound  with 
thread)  at  c  and  g  with  the  glass  tubes  c  d  and  g  h.  A  rubber  tube  is 
drawn  over  the  lower  end  of  g  h  to  protect  it  from  fracture.  B  is  a 
glass  vessel  containing  10  per  cent,  soda  solution .  A  measuring  tube 
graduated  to  0*1  c.c.,  of  not  too  great  diameter,  filled  with  previously 
boiled  soda  solution,  is  supported  so  that  its  open  end  is  under  the 
surface  of  the  liquid  in  B. 

The  solution  of  the  nitrate  in  the  flask  is  further  concentrated 
by  boiling,  and  finally  the  lower  end  of  the  tubeefg  h  is  brought 
into  the  soda  solution  so  that  a  part  of  the  steam  escapes  through 
it.  After  a  few  minutes  the  rubber  tube  at  g  is  pressed  together 
with  the  fingers ;  if  the  air  has  been  completely  displaced  from 
the  flask  by  boiling,  the  soda  solution  will  rise  suddenly  in  the  tube 
as  in  a  vacuum,  and  a  slight  blow  against  the  finger  will  be  percep- 
tible. In  this  case,  the  rubber  tube  at  g  is  closed  with  a  clamp 
and  the  steam  is  allowed  to  escape  through  abcdnniil  only  10  c.c. 

*  Annal.  d.  Chem.  u.  Pharm.  106,  217. 
f  Zeitschr.  fur  anal.  Chem.  1870,  400. 

|  Anleitung  zur  Untersuchung  von  Wasser,  von  W.  Kubel,  Zweite  Auflage 
von  F.  Tiemann,  Braunschwerg  bei  Fr.  Yieweg  u.  Sohn.  1870,  s.  55. 


474 


DETERMINATION. 


[§  149. 


of  fluid  remain  in  the  flask.  The  lamp  is  now  removed  and  the 
rubber  tube  at  c  is  closed  with  a  clamp,  and  the  tube  c  d  filled  by 
a  jet  of  water.  If  an  air  bubble  remains  in  the  rubber  tube  at  0, 
it  must  be  removed  by  pressure  with  the  fingers.  The  graduated 
measuring  tube  is  now  brought  over  the  upcurved  end  of  the  evo- 
lution tube  efg  h  so  that  the  end  rises  in  it  2-3  cm.  The  flask 
must  next  be  allowed  to  stand  a  few  minutes  until  a  partial  vacuum  is 
produced  in  it,  which  is  manifested  by  a  contraction  of  the  rubber 
tubes  at  c  and  g.  A  nearly  saturated  solution  of  ferrous  chloride 
is  poured  into  a  small  beaker,  the  upper  part  of  which  is  marked 


Fig.  67. 

so  as  to  show  the  space  occupied  by  20  c.c.  ;  two  other  beakers 
must  also  be  at  hand  partly  filled  with  concentrated  hydrochloric 
acid.  The  tube  c  d  is  nowT  dipped  into  the  ferrous  chloride  solution, 
and  the  clamp  at  c  is  loosened  until  15-20  c.c.  are  drawn  into  the 
flask.  The  ferrous  chloride  remaining  in  the  tube  is  next  removed 
by  drawing  in  a  small  quantity  of  hydrochloric  acid  in  two  suc- 
cessive portions.  Small  bubbles  may  frequently  be  observed  at 
5,  occasioned  by  evolution  of  hydrochloric  gas  caused  by  dimin- 
ished pressure  in  the  flask.  They  disappear  almost  completely  so 
soon  as  the  pressure  rises. 


g  149.]  NITRIC    ACID.  475 

Heat  is  applied,  at  first  very  gently,  until  the  rubber  tubes  at  c 
and  g  are  slightly  expanded ;  then  the  rubber  tube  at  g  is  held  com- 
pressed by  the  fingers,  the  clamp  being  removed,  until  the  pressure 
becomes  stronger,  when  the  gas  is  allowed  to  pass  over  to  the  grad- 
uated tube.  Toward  the  end  of  the  operation  heat  is  increased  and 
distillation  continued  until  the  volume  of  gas  in  the  measuring 
tube  no  longer  increases.  The  hydrochloric  gas,  abundantly 
evolved  in  the  last  part  of  the  process,  is  absorbed  with  violence 
by  the  soda  solution  with  a  peculiar  clattering  sound ;  there  is  no 
danger,  however,  of  breaking  the  evolution  tube  if  care  has  been 
taken  to  enclose  the  lower  end  with  a  rubber  tube  as  above  directed. 

The  measuring  tube  is  brought  into  a  large  cylinder  containing 
cold  water,  best  of  15-18°  C.,  and  by  means  of  some  suitable  fix- 
ture held  wholly  submerged  in  the  same.  The  transfer  is  effected 
with  the  help  of  a  small  porcelain  dish  filled  with  soda  solution. 

After  15-20  minutes,  the  temperature  of  the  water  in  the 
cylinder  is  ascertained  with  a  sensitive  thermometer,  and  the  state 
of  the  barometer  is  also  observed.  Then  the  tube  is  taken  hold 
of  at  the  upper  end  with  a  strip  of  paper  or  cloth,  in  order  to  avoid 
imparting  heat  to  it  by  direct  contact  of  the  hand,  and  drawn 
up  perpendicularly  so  far  that  the  level  of  the  fluids  within  and 
without  it  exactly  coincide,  and  the  volume  of  the  gas  is  read  off. 
From  the  data  thus  obtained,  the  volume  which  the  dry  gas  would 
occupy  at  0°  C.  and  760  mm.  bar.  pressure  is  to  be  computed.  (See 
p.  836,  on  Calculation  of  Analyses.)  1  c.c.  JSTaO,  at  0°  C.  and 
760  mm.  bar.  pressure  corresponds  to  •  002413  grm.  N2OS. 

A  condition  indispensable  for  the  success  of  the  operation  is 
the  complete  expulsion  of  air  from  the  apparatus  in  the  beginning. 
When  an  abundant  quantity  of  nitric  acid  is  present  in  the  sub- 
stance, enough  to  produce  about  80  c.c.  nitrogen  dioxide  is  a  suit- 
able quantity  to  use  for  its  determination,  and  a  somewhat  larger 
quantity  of  ferrous  chloride  and  hydrochloric  acid  than  above  indi- 
cated may  be  used.  An  unnecessary  amount  of  these  reagents 
should,  however,  be  avoided,  since  it  is  difficult  to  boil  a  small  quan- 
tity of  nitrogen  dioxide  out  of  a  large  volume  of  liquid. 

This  method  is  easy  to  carry  out  and  gives  satisfactory  results. 
It  has  been  selected  for  description  and  recommendation  here  out 
of  a  great  number  of  methods,  not  mentioned  in  this  volume, 
which  have  been  proposed  and  more  or  less  used  for  determination 
of  nitric  acid. 


476  DETERMINATION.  [§  150. 

e.  Methods  in  which  the  Nitrogen  of  the  Nitric  Acid  is  sep- 
arated and  measured  in  the  gaseous  form. 

These  methods  are  more  particularly  suitable  for  analyzing 
nitrates  which  are  decomposed  by  ignition  into  oxide  or  metal  and 
oxides  of  nitrogen  ;  they  will  be  found  in  the  Section  on  the  Ulti- 
mate Analysis  of  Organic  Bodies,  §  184.  MARIGNAC  employed 
them  to  analyze  rnercurous  nitrates.  BROMEIS  analyzed  nitrite,  &c., 
of  lead  by  a  similar  method,  recommended  by  BUNSEN.  In  cases 
where  it  is  intended  to  determine  the  water  of  the  analyzed  nitrate 
in  the  direct  way,  such  methods  are  almost  indispensable.* 

§150. 
2.  CHLORIC  ACID. 

I.  Determination. 

Free  chloric  acid  in  aqueous  solution  may  be  determined  by 
converting  it  into  hydrochloric  acid  by  the  agency  of  nascent 
hydrogen  (II.,  &),  and  determining  the  acid  formed,  as  directed  in 
§  141  ;  or  by  saturating  with  solution  of  soda,  evaporating  the  fluid, 
and  treating  the  residue  as  directed  in  II.,  a  or  c. 

II.  Separation  of  Chloric  Acid  from  the   Bases   and 
Determination  of  the  Acid  in  Chlorates. 

a.  After  BuNSEN.f  "When  warm  hydrochloric  acid  acts  upon 
chlorates,  the  latter  are  reduced  ;  as  this  reduction  is  not  attended 
with  separation  of  oxygen,  the  following  decompositions  may  take 
place  : 


C1205          2       C1206      3  C120    C1205  2       C1205  C1205      12C1 

2HC1    j  g1^3  4HC1    I  2  H2Q    6HC1    |  Jg1^    8HC1    |  g^Q    10HC1  ]  5H*<> 

Which  of  these  products  of  decomposition  may  actually  be  formed, 
whether  all  or  only  certain  of  them,  cannot  be  foreseen.  But  no 
matter  which  of  them  may  be  formed,  they  all  of  them  agree  in 
this,  that,  in  contact  with  solution  of  potassium  iodide,  they  liber- 
ate for  every  2  mol.  chloric  acid  (HC1O3),  or  1  mol.  C12O5  in  the 
chlorate,  12  at.  iodine.  1522*2  of  iodine  liberated  correspond  accord- 
ingly to  150-92  C13O5.  The  analytical  process  is  conducted  as  des- 
cribed §  142,  1. 

*  See  also  Gibbs,  Am.  Journ.  Sci.,  xxxvii.  350. 
f  Annal.  d.  Chem.  u.  Pharm.  86,  282. 


jj  150.]  CHLOKIC   ACID.  477 

l>.  After  SESTINI.*  To  the  concentrated  aqueous  solution  of 
the  weighed  chlorate  add  a  piece  of  zinc  and  then  some  pure 
dilute  sulphuric  acid  and  allow  to  stand  for  some  time  (with  0.1 
grin,  potassium  chlorate  half  an  hour  is  sufficient).  By  the  nas- 
cent hydrogen  the  chloric  acid  is  converted  into  hydrochloric  acid, 
which,  after  removal  and  rinsing  of  the  zinc,  is  determined  accord- 
ing to  §  141.  To  use  the  volumetric  method  (§  141,  £,  a\  the  sul- 
phuric acid  is  first  precipitated  with  barium  nitrate,  then  the  zinc 
and  excess  of  barium  with  sodium  carbonate,  the  liquid  is  filtered 
and  neutralized,  then  potassium  chromate  is  added,  and  finally 
standard  silver  solution. 

c.  The  basic  radicals  are  determined  with  advantage  in  a  sepa- 
rate portion,  by  converting  the  chlorate  either  by  very  cautious 
ignition,  or  by  warming  with  hydrochloric  acid  into  chloride. 

The  estimation  of  hypochlorous  acid  will  be  described  in  the 
Special  Part,  article  "  Chlorimetry." 

\  Zeitschrift  f.  analyt.  Chem.  1,  500. 


SECTION  V. 

SEPAKATION    OF   BODIES. 

§151. 

WHEN  only  one  basic  or  one  acid  radical  is  present,  the  method 
of  its  determination  has  been  considered  in  the  previous  Section. 
When  more  than  one  basic  or  more  than  one  acid  radical  is  pres- 
sent,  the  methods  of  separating  and  determining  them  will  be 
described  in  the  present  Section. 

The  separation  of  bodies  may  be  effected  in  three  ways :  viz.,  #, 
by  direct  analysis ;  b,  by  indirect  analysis ;  c,  by  estimation  by 
difference. 

By  direct  analysis,  we  understand  the  actual  separation  of  rad- 
icals or  elements.  Thus,  we  separate  potassium  from  sodium  by 
platinic  chloride ;  copper  from  tin  by  nitric  acid ;  arsenic  from 
iron  by  hydrogen  sulphide ;  iodine  from  chlorine  by  palladious 
nitrate ;  carbon  from  potassium  nitrate  by  water,  &c.,  &c.  In 
direct  analysis  we  render  one  body  insoluble,  while  the  others 
remain  in  solution,  or  vice  versa,  or  we  volatilize  one  body,  leav- 
ing the  others  behind,  or  we  effect  actual  separation  in  some  other 
manner.  This  is  the  mode  of  analysis  most  frequently  employed. 
It  generally  deserves  the  preference  where  choice  is  permitted. 

We  term  an  analysis  indirect  if  it  does  not  effect  the  actual  sep- 
aration of  the  bodies,  but  causes  certain  changes  which  enable  us 
to  calculate  their  quantity.  Thus,  the  quantity  of  potassium  and 
sodium  in  a  mixture  of  compounds  of  the  two  may  be  determined 
by  converting  them  into  chlorides,  weighing  the  latter,  and  deter- 
mining the  chlorine  (§  152,  3). 

Finally,  if  we  weigh  two  bodies  together,  determine  one  of  them, 
and  subtract  its  weight  from  that  of  the  two,  we  shall  find  the 
weight  of  the  other  body.  In  this  case  the  second  body  is  said  to 
be  estimated  by  difference.  Thus,  aluminium  may  be  determined 
when  its  oxide  is  mixed  with  ferric  oxide,  by  weighing  the  mix- 
ture and  determining  the  iron  volumetrically. 


[§  151.  SEPARATION   OF   BODIES.  479 

Indirect  analysis  and  estimation  by  difference  may  be  employed 
in  an  exceedingly  large  number  of  cases ;  but  their  use  is  as  a  rule 
only  to  be  recommended  where  good  methods  of  true  separation 
are  wanting.  The  special  cases  in  which  they  are  preferable  to 
direct  analysis  cannot  be  all  foreseen ;  those  alone  are  pointed 
out  which  are  of  more  frequent  occurrence.  As  regards  the  calcu- 
lations required  in  indirect  analysis,  I  have  given  general  direc- 
tions under  "  the  Calculation  of  Analysis  ;"  wherever  it  appeared 
judicious,  I  have  added  the  necessary  directions  to  the  description 
of  the  method  itself. 

I  have  retained  our  former  subdivision  into  groups,  and,  as  far 
as  practicable,  systematically  arranged,  first,  the  general  separation 
of  all  the  bodies  belonging  to  one  group  from  those  of  the  preced- 
ing groups ;  secondly,  the  separation  of  the  individual  bodies  of  one 
group  from  all  or  from  certain  bodies  of  the  preceding  groups ; 
and  finally,  the  separation  of  bodies  belonging  to  one  and  the  same 
group  from  each  other.  I  think  I  need  scarcely  observe  that  the 
general  methods  which  serve  to  separate  the  whole  of  the  bodies  of 
one  group  from  those  of  another  group  are  also  applicable  to  the 
separation  of  every  individual  body  of  the  one  group  from  one  or 
several  bodies  of  the  other  group.  It  must  not  be  understood  that 
the  more  special  methods  are  necessarily  in  all  cases  preferable  to 
the  more  general  ones.  As  a  rule,  it  must  be  left  to  individual 
chemists  to  decide  for  themselves  in  each  special  case  which  method 
should  be  adopted.  With  respect  to  the  general  methods  for  sepa- 
rating one  group  from  another,  I  would  observe  that  those  adduced 
appeared  to  me  more  adapted  to  the  purpose  than  others,  but 
still  there  may  be  others  that  are  equally  suitable,  and  in  special 
cases  even  more  so.  A  wide  field  is  here  open  to  the  ingenuity 
of  the  analyst. 

The  methods  given  for  the  separation  of  both  basic  and  acid 
radicals  are  generally  based  upon  the  supposition  that  they  are  in 
the  form  of  free  acids  or  bases,  or  in  the  form  of  salts  soluble  in 
water.  Wherever  this  is  not  the  case,  special  mention  is  made  of 
the  circumstance. 

From  among  the  host  of  proposed  methods,  I  have,  as  far  as 
practicable,  chosen  those  which  have  been  sanctioned  by  experience 
and  are  distinguished  for  accurate  results.  In  cases  where  two 
methods  were  on  a  par  with  each  other  as  regards  these  two  points, 
I  have  either  given  both  or  selected  the  more  simple  one.  Methods 


480  SEPARATION    OF   BODIES.  [§  151. 

which  experience  has  shown  to  be  defective  or  fallacious  have  been 
altogether  omitted.  I  have  endeavored  to  point  out,  as  far  as  pos- 
sible?  the  particular  circumstances  under  which  either  the  one  or 
the  other  of  several  methods  deserves  the  preference. 

Where  the  accuracy  of  an  analytical  method  has  been  estab- 
lished already,  in  Section  IY.,  no  furthur  statements  are  made  on 
the  subject  here.  Paragraphs  of  former  Sections  deserving  par- 
ticular attention  are  referred  to  in  parentheses. 
>  The  extension  of  chemical  science  introduces  almost  every  day 
new  analytical  methods  of  every  description,  which  are,  rightly  or 
wrongly,  preferred  to  the  older  methods;  the  present  time  may 
therefore  be  looked  upon  in  this,  as  in  so  many  other  respects,  as  a 
period  of  transition,  in  which  the  new  strives  more  than  ever  to 
overcome  and  supplant  the  old.  I  make  this  remark  to  show  the 
impossibility  of  always  adding  to  the  description  of  a  method  an 
opinion  of  its  usefulness  and  accuracy,  and  also  to  point  out  the 
importance,  under  such  circumstances,  of  a  proper  systematic 
arrangement.  I  have  in  this  Section  generally  arranged  the  vari- 
ous analytical  methods  upon  the  bases  of  their  scientific  principles, 
firmly  persuaded  that  this  will  greatly  tend  to  facilitate  the  study 
of  the  science,  and  will  lead  to  endeavors  to  apply  known  princi- 
ples to  the  separation  of  other  bodies  besides  those  to  which  they 
are  already  applied,  or  to  apply  new  principles  where  experience 
has  proved  the  old  ones  fallacious,  and  the  methods  based  on  them 
defective. 

I  conclude  these  introductory  remarks  with  the  important  cau- 
tion to  the  student  never  to  look  upon  a  separation  as  successfully 
accomplished  ~before  he  has  convinced  himself  that  the  weighed  pre- 
cipitates, <&c.,  are  pure  and  more  particularly  free  from  those 
bodies  from  which  it  was  intended  to  separate  them. 


[§  152.  BASES    OF   GROUP   I.  481 

I.  SEPARATION  OF  THE   BASIC    RADICALS  FROM  EACH  OTHER. 

First  Group. 

POTASSIUM SODIUM AMMONIUM — (LITHIUM). 

§152. 

INDEX.     The  numbers  refer  to  those  in  the  margin. 

Potassium  from  sodium,  1,  2,  6. 

"          ammonium,  4,  5. 
Sodium  from  potassium,  1,  2,  6. 

"          ammonium,  3,  4,  5. 
Ammonium  from  potassium,  4,  5. 
"          sodium,  3,  4,  5. 
(Lithium  from  the  other  alkalies,  7,  8,  9.) 

1.  Methods  based  upon  the  different  degrees  of  Solubility 
in  Alcohol,  of  Sodium  Platinic  Chloride,  and  Potassium 
Platinic  Chloride. 

a.  POTASSIUM  FROM  SODIUM. 

It  is  an  •  indispensable  condition  in  this  method  that  the  1 
two  alkalies  should  exist  in  the  form  of  chlorides.  If,  there- 
fore, they  are  present  in  any  other  form,  they  must  be  first  con- 
verted into  chlorides,  which  in  most  cases  may  be  effected  by 
evaporation  with  hydrochloric  acid  in  excess;  in  the  case  of 
nitrates,  the  evaporation  with  hydrochloric  acid  must  be 
repeated  4 — 6  times  till  the  weight  of  the  gently  ignited  mass 
ceases  to  diminish.  In  presence  of  sulphuric  acid,  phosphoric 
acid,  and  boracic  acid,  this  simple  method  will  not  answer.  For 
the  methods  of  separating  the  alkalies  from  the  two  latter  acids 
and  converting  them  into  chlorides,  see  §§  135  and  136;  The 
presence  of  sulphuric  acid  being  a  circumstance  of  rather  fre- 
quent occurrence,  the  way  of  meeting  this  contingency  is  given 
below  (2). 

Determine  the  total  quantity  of  the  sodium  chloride  and 
potassium  chloride*  (§§  97,  98),  dissolve  in  the  least  quantity 


*  Never  take  the  weight  of  the  alkali  chlorides  without  convincing  yourself  of 
their  purity  by  dissolving  them  in  water,  which  should  give  a  clear  solution,  and 
testing  the  solution  with  ammonia  and  ammonium  carbonate,  which  must  throw 
down  no  precipitate.  It  may  be  thought,  perhaps,  that  a  matter  so  simple  need 
not  be  mentioned  here ;  still  I  have  found  that  neglect  in  this  respect  is  by  no 
means  uncommon. 


482  SEPARATION.  [§  152. 

of  water,  add  to  the  fluid  in  a  porcelain  dish  an  excess  of  a 
strong  aqueous  solution  of  platinic  chloride  as  neutral  as  pos- 
sible. Enough  platinum  solution  should  be  added  to  convert 
the  sodium  as  well  as  the  potassium  into  platinochloride.  It 
is  best  to  use  a  solution  of  known  strength  and  to  calculate 
roughly  how  much  should  be  added.  Evaporate  on  the  water- 
bath  nearly  to  dryness  (the  water  in  the  bath  should  never 
actually  boil,  and  the  sodium  platinic  chloride  should  not  lose 
its  water  of  crystallization),  treat  the  residue  with  alcohol  of 
from  -86  to  *S7  sp.  gr.,  cover  the  dish  with  a  glass  plate,  and 
allow  to  stand  a  few  hours,  with  occasional  stirring.  If  the  super- 
natant fluid  is  not  deep  yellow,  this  is  a  proof  that  the  quantity 
of  platinic  chloride  used  is  insufficient.  When  the  precipitate 
has  settled,  pour  off  the  clear  fluid  through  a  filter  and  exam- 
ine the  precipitate  most  minutely,  if  necessary  with  the  aid 
of  a  microscope.  If  it  is  a  heavy  yellow  powder  (sufficiently 
magnified,  small  octahedral  crystals)  it  is  the  pure  potassium  pla- 
tinic chloride.*  Then  transfer  it — best  with  the  aid  of  the  fil- 
trate— to  the  filter,  wash  it  with  spirit  of  '86  to  '87  sp.  gr.  and 
proceed  according  to  §  97,  3  a.  (Instead  of  weighing  the  double 
chloride  or  the  platinum  obtained  from  it,  you  may  ignite  gen- 
tly in  hydrogen,  extract  the  potassium  chloride  with  water, 
and  weigh  this  or  titrate  the  chlorine  in  it  by  §  141,  I.,  5,  «). 
If,  on  the  contrary,  white  saline  particles  (sodium  chloride) 
are  to  be  seen  mixed  with  the  yellow  crystalline  powder,  pla- 
tinic chloride  has  been  wanting,  the  whole  of  the  sodium  chlo- 
ride not  having  been  completely  converted  into  sodium  platinic 
chloride.  In  this  case  the  precipitate  in  the  dish  must  be 
treated  with  some  water,  till  all  the  sodium  chloride  is  dis- 
solved, a  fresh  portion  of  platinic  chloride  is  added,  the  whole 
evaporated  nearly  to  dryness,  and  the  above  examination 
repeated.  The  quantity  of  the  sodium  is  usually  estimated 
by  subtracting  from  the  united  weight  of  the  sodium  chloride 
and  potassium  chloride  the  weight  of  the  latter,  calculated 
from  that  of  the  potassium  platinic  chloride. 

To  make  quite  sure  that  the  potassium  has  completely  sep- 


*  If  small  tesseral  crystals  are  visible  of  .a  dark  orange-yellow  color,  and 
relatively  large  size,  and  appearing  transparent  by  transmitted  light,  then  the 
double  chloride  contains  lithium  platinic  chloride  (JENZSCH,  Pogg.  Ann.  104, 
102). 


§  152.]  BASES   OF  GROUP   I.  483 

sirated,  it  is  advisable  to  add  to  the  filtrate  some  water,  some 
more  platinic  chloride,  and  if  the  quantity  of  sodium  is  only 
small,  also  some-  sodium  chloride ;  evaporate  on  the  water-bath 
nearly  to  dry  ness,  at  a  temperature  not  exceeding  75°  (BISCHOF), 
and  treat  the  residue  in  the  manner  just  described.  In  order 
to  diminish  the  solvent  action  of  the  alcohol  on  the  potassium 
platinic  chloride,  J  ether  may  be  now  mixed  with  it.  Should 
this  operation  again  leave  a  small  undissolved  residue  of  potas- 
sium platinic  chloride,  it  is  filtered  off,  best  on  a  separate  filter, 
and  first  washed  with  alcohol  and  ether.  As,  however,  this 
remainder  of  the  double  salt  is  generally  impure,  dissolve  it  on 
the  filter  with  boiling  water,  evaporate  with  a  few  drops  of  pla- 
tinic chloride,  treat  the  residue  with  alcohol,  and  if  any  potas- 
sium salt  remains,  determine  it  either  with  the  principal  quan- 
tity or  by  itself. 

If  you  are  not  satisfied  with  an  indirect  estimation  of 
the  sodium,  one-  of  the  following  direct  methods  may  be 
employed,  a.  Evaporate  the  filtrate  till  the  spirit  has  gone  off, 
dilute,  digest  the  solution  with  small  pure  iron  filings  till  the 
platinum  is  all  thrown  down,  filter,  add  chlorine  water  till  the 
ferrous  is  converted  into  ferric  chloride,  precipitate  with  ammo- 
nia, filter  off  the  ferric  hydroxide,  and  determine  the  sodium 
chloride  in  the  filtrate,  ft.  Evaporate  the  filtrate,  finally  in  a 
porcelain  crucible,  to  dryness,  heat  the  residue  to  low  redness 
in  a  current  of  hydrogen,  extract  with  water,  and  determine 
the  sodium  chloride  in  the  solution.  For  small  quantities  of 
fluid  this  method  will  be  found  convenient,  y.  A.  MITSCHEK- 
LICH  recommends  to  mix  the  filtrate  with  sulphuric  acid,  evapo- 
rate to  dryness,  ignite  the  residue,  extract  the  sodium  sul- 
phate with  water,  and  determine  it  according  to  §  98, 1.  These 
methods,  of  course,  yield  the  sodium  salt  in  a  pure  condition 
only  when  the  separation  of  the  potassium  has  been  perfect. 
They  present  the  advantage  that  the  sodium  salt  is  brought 
under  one's  eyes  and  may  be  tested  after  weighing. 

Should  the  solution  contain  sulphuric  acid,  it  may  be  in     2 
presence  of  hydrochloric  acid  or  of  some  volatile  acid,  convert 
the  alkalies  first  into  normal  sulphates  (§§  97,  98),  and  weigh 
them  as  such.     For  the  estimation  of  the  potassium,  one  of  tie 
two  following  methods  may  be  used : 

a.  First  convert  the  sulphates  into  chlorides  and  then  pro- 


484  SEPARATION.  [§  152. 

ceed  as  above.  For  this  purpose  barium  salts  were  formerly 
employed,  or,  better,  an  alcoholic  solution  of  strontium  chloride. 
The  barium  sulphate,  however,  carries  down  considerable  quan- 
tities of  alkali  salt,  and  the  strontium  sulphate  noticeable 
quantities ;  hence  the  employment  of  these  reagents,  more  par- 
ticularly barium,  cannot  be  recommended.  H.  ROSE  advises 
repeated  ignition  of  the  alkali  sulphates  with  ammonium 
chloride  till  the  weight  remains  constant ;  this  process  is  simple 
and  well  adapted  for  small  quantities ;  no  loss  of  alkali  need  be 
feared  if  the  heat  is  not  unnecessarily  raised.  L.  SMITH  advises 
the  use  of  lead  salts.  Dissolve  the  alkali  sulphate,  precipitate 
with  pure  neutral  lead  acetate,  avoiding  a  large  excess,  add 
some  alcohol,  filter,  precipitate  the  excess  of  lead  with  sulphuric 
acid,  and  evaporate  to  dryness  with  addition  of  sulphuric  acid. 
This  method,  when  carefully  conducted,  yields  excellent  results. 

/?.  Precipitate  the  potash  directly  out  of  the  solution  of  the 
sulphates.  R.  FINKENER*  gives  the  following  process:  To  the 
rather  dilute  solution  of  the  salts  in  a  capacious  porcelain  dish 
add  platinic  chloride  in  quantity  more  than  sufficient  to  throw 
down  all  the  potassium,  evaporate  on  a  water-bath  down  to  a 
few  c.c.,  allow  to  cool,  add,  at  first  in  small  quantities,  20 
times  the  volume  of  a  mixture  of  2  parts  absolute  alcohol  and 
1  part  ether,  with  stirring ;  filter  after  a  short  time,  and  wash 
the  precipitate  with  alcohol  and  ether  till  the  washings  are 
colorless.  If,  when  the  alcohol  and  ether  are  first  added,  a 
strong  aqueous  solution  of  sodium  sulphate  separates,  add  some 
hydrochloric  acid  till  the  fluids  mix.  Dry  the  precipitate  con- 
sisting of  potassium  platinic  chloride  and  sodium  sulphate, 
heat  with  the  filter  in  a  porcelain  crucible  till  the  filter  is  car- 
bonized, then  in  a  current  of  hydrogen  to  scarcely  visible 
redness  extract  the  residue  with  hot  water,  ignite  the  platinum 
in  the  air,  weigh  and  calculate  from  the  weight  the  quantity  of 
potassium. 

The  separation  of  potassium  from  sodium  by  platinic 
chloride  gives  results  which  are  fully  satisfactory,  and  at  all 
events  far  more  exact  than  any  method  depending  on  another 
principle  ;  provided  that  the  platinum  solution  is  pure  and  the 
operations  have  been  carefully  performed  in  accordance  with 
the  directions.  If  you  have  any  occasion  to  doubt  the  perfect 


*  H.  ROSE,  Handbuch  der  anal.  Chem.  6  Aufl.  von  FINKENER,  ii.  923. 


BASES    OF   GROUP    I.  485 

purity  of  the  weighed  double  salt,  you  may  always  dissolve  it 
in  boiling  water,  evaporate  with  addition  of  a  little  platinum 
solution,  and  reweigh  the  salt  thus  purified. 

I.  AMMONIUM  FROM  SODIUM. 

The  process  is  conducted  exactly  as  in  a,  when  the  alka-  3 
lies  are  present  as  chlorides.  See  also  §  99,  2.  If  potassium 
also  is  present,  the  precipitate  produced  by  platinic  chloride  is  a 
mixture  of  ammonium  platinic  chloride  and  potassium  platinic 
chloride ;  in  which  case  the  weighed  precipitate  is  cautiously 
ignited  for  a  sufficient  length  of  time,  but  not  too  strongly, 
until  the  ammonium  chloride  is  expelled,  the  gentle  ignition 
continued  in  a  stream  of  hydrogen  or  with  addition  of  oxalic 
acid,  the  residue  extracted  with  water,  a  few  drops  of  hydro- 
chloric acid  added  if  oxalic  acid  was  employed,  and  the  potas- 
sium chloride  in  the  solution  determined  as  directed  §  97,  2. 
The  weight  found  is  calculated  into  potassium  platinic  chloride, 
and  the  result  deducted  from  the  weight  of  the  whole  precipi- 
tate :  the  difference  gives  the  ammmonium  platinic  chloride. 
The  weighing  of  the  separated  platinum  affords  a  good  control. 
The  method  is  seldom  employed,  as  that  given  in  2  yields  more 
exact  results. 

2.  Methods  based  upon  the  Volatility  of  Ammonium 
/Salts  and  Ammonia. 

AMMONIUM  FROM  POTASSIUM  AND  SODIUM. 

a.  The  salts  of  the  alkalies  to  be  separated  contain  the  same     4 
volatile  add,  and  admit  of  the  total  expulsion  of  their  water  by 
drying  at  100°,  without  losing  ammonia  (e.g.,  the  chlorides). 

Weigh  the  total  quantity  of  the  salts  in  a  platinum  crucible, 
and  heat,  with  the  lid  on,  gently  at  first,  but  ultimately  for 
some  time  to  faint  redness ;  let  the  mass  cool,  and  weigh.  The 
decrease  of  weight  gives  the  quantity  of  the  ammonium  salt. 
If  the  acid  present  is  sulphuric  acid,  you  must,  in  the  first 
place,  take  care  to  heat  very  gradually,  as  otherwise  you  will 
suffer  loss  from  the  decrepitation  of  ammonium  sulphate  ;  and, 
in  the  second  place,  bear  in  mind  that  part  of  the  sulphuric 
acid  of  the  ammonium  sulphate  remains  with  the  fixed  alkali 
sulphates,  and  that  you  must  accordingly  convert  them  into 
normal  salts,  by  ignition  in  an  atmosphere  of  ammonium  car- 


486  SEPARATION.  [§  152. 

bonate,  before  proceeding  to  determine  their  weight  (compare 
§§  97  and  98).  Ammonium  chloride  cannot  be  separated  in 
this  manner  from  fixed  alkali  sulphates,  as  it  converts  them, 
upon  ignition,  partly  or  totally  into  chlorides. 

1}.  Some  one  or  other  of  the  conditions  given  in  "a "  is  not 
fulfilled. 

If  it  is  impracticable  to  alter  the  circumstances  by  simple  5 
means,  so  as  to  make  the  method  a  applicable,  the  fixed  alkalies 
and  the  ammonium  must  be  determined  separately  in  different 
portions  of  the  substance.  The  portion  in  which  it  is  intended 
to  determine  the  potassium  and  sodium  is  gently  ignited  until 
ammonium  is  completely  expelled.  The  fixed  alkalies  are  con- 
verted, according  to  circumstances,  into  chlorides  or  sulphates, 
and  treated  as  directed  in  1,  2,  or  6.  The  ammonium  is  esti- 
mated in  another  portion  according  to  §  99,  3. 

3.  Indirect  Methods. 

Of  course,  a  great  many  of  these  may  be  devised ;  but  the     6 
following  is  the  only  one  in  general  use. 

POTASSIUM  FROM  SODIUM. 

Convert  both  alkalies  into  chlorides  (§§  97  and  98),  and 
weigh  as  such ;  estimate  chlorine  (§  141) ;  and  from  the 
amount  of  this  calculate  the  quantities  of  the  sodium  and 
potassium  (see  "  Calculation  of  Analysis"  *). 

The  indirect  method  of  determining  sodium  and  potassium 
is  applicable  only  in  the  analysis  of  mixtures  containing  toler- 
ably large  quantities  of  both  bases ;  but  where  this  is  the  case, 
the  process  answers  very  well,  affording  also,  more  particularly, 
the  advantage  of  expedition,  if  the  chlorine  in  the  weighed 
chlorides  is  titrated  (§  141,  I.,  5). 

Supplement  to  the  First  Group. 
SEPARATION  OF  LITHIUM  FROM  THE  OTHER  ALKALIES. 
Lithium  may  be  separated  from. potassium  and  sodium  in  the     7 
indirect  way,  and  by  two  direct  methods : 

a.  Treat  the  nitrates  or  the  chlorides,  dried  at  120°,  with  a 
mixture  of  equal  volumes  of  absolute  alcohol  and  anhydrous 
ether,  digest  at  least  for  24  hours,  with  occasional  shaking  (the 

*  Other  methods  are  given  by  STOLBA  (Zeitschr.  f .  anal.  Chem.  2,  397)  and 
MOIIR  (7*.  7,  173). 


§  152.]  BASES   OF   GROUP   I.  487 

salts  must  be  completely  disintegrated),  decant  rapidly  on  to  a 
filter  covering  the  funnel,  and  treat  the  residue  again  several 
times  with  smaller  portions  of  the  mixture  of  alcohol  and  ether. 
Determine,  on  the  one  part,  the  undissolved  potassium  and 
sodium  salts ;  on  the  other,  the  dissolved  lithium  salt,  by  dis- 
tilling the  fluid  off,  and  converting  the  residue  into  sulphate. 
This  method  is  apt  to  give  too  much  lithium,  as  the  potassium 
and  sodium  salts,  especially  the  chlorides,  are  not  absolutely 
insoluble  in  a  mixture  of  alcohol  and  ether.  The  results  may 
be  rendered  more  accurate  by  treating  the  impure  lithium  salt, 
obtained  by  distilling  off  the  ether  and  alcohol,  once  more  with 
alcohol  and  ether,  with  addition  of  a  drop  of  nitric  or  hydro- 
chloric acid,  adding  the  residue  left  to  the  principal  residue, 
and  then  converting  the  lithium  salt  into  sulphate.  If  the 
salts,  which  it  is  intended  to  treat  with  alcohol  and  ether,  have 
been  ignited,  however  so  gently,  caustic  lithia  is  formed — in 
the  case  of  the  chloride  by  the  action  of  water — and  lithium 
carbonate  by  attraction  of  carbonic  acid ;  in  that  case  it  is  neces- 
sary, therefore,  to  add  a  few  drops  of  nitric  or,  as  the  case  may 
be,  hydrochloric  acid,  in  the  process  of  digestion. 

If  we  have  to  separate  the  sulphates,  they  must  be  converted 
into  nitrates  or  chlorides  before  they  can  be  subjected  to  the 
above  method.  This  conversion  is  best  effected  by  means  of 
lead  salts,  see  2.  Ignition  with  ammonium  chloride  does  not 
answer  for  lithium  sulphate,  nor  can  the  sulphuric  acid  be 
removed  by  barium,  or  strontium,  as  the  precipitated  sulphates 
would  contain  lithium  (DiEHL*). 

£>.  Weigh  the  mixed  alkalies,  best  in  form  of  sulphates,  and  8 
then  determine  the  lithium  as  phosphate  according  to  §  100. 
If  the  quantity  of  lithium  is  relatively  very  small,  convert  the 
weighed  sulphates  into  chlorides  (7),  separate,  in  the  first  place, 
the  principal  amount  of  the  potassa  and  soda  by  means  of  alco- 
hol (§  100),  and  then  determine  the  lithium  (MAYER  f). 

c.  When  exact  results  are  required,  the  indirect  method  is     9 
to  be  preferred.     Proceed  first  according  to  rt,  evaporate  the 
spirituous  solution  of  the  lithium  chloride  containing  the  remain- 
der of  the  other  chlorides  to  dryness,  heat  moderately,  weigh, 
dissolve  in  water,  estimate  the  chlorine,  and  calculate  therefrom 

*  Annal  d.  Chem.  u.  Pharm.  121,  98.  \  Ib.  98,  193. 


488  SEPARATION.  [§  153. 

the  lithium  and  sodium  or  potassium.  BUNSEN  *  also  applied 
the  method  to  the  indirect  estimation  of  lithium  in  presence  of 
potassium  and  sodium  by  removing  the  silver  from  the  filtrate, 
and  separating  the  potassium  with  platinum,  But  I  must  here 
point  out,  that  according  to  JENZSCH  f  the  potassium  double  salt 
will  contain  lithium  apparently  in  the  form  of  the  platino- 
chloride  of  potassium  and  lithium. 

The  sulphuric  acid  in  weighed  quantities  of  the  sulphates 
of  lithium,  and  of  potassium  and  sodium,  cannot  be  determined 
as  barium  sulphate  (see  end  of  7). 

The  separation  of  lithium  from  ammonium  may  be  effected 
like  that  of  potassium  and  sodium  from  ammonium  (4  and  5). 


Second  Group. 

BARIUM STRONTIUM CALCIUM — -MAGNESIUM. 

I.  SEPARATION  OF  THE  BASIC  RADICALS  OF  THE  SECOND  GROUP  FROM 

THOSE    OF    THE    FlRST. 

§153. 

INDEX.     (The  numbers  refer  to  those  in  the  margin.) 
Barium  from  potassium  and  sodium,  10,  12. 

ammonium,  11. 
Strontium  from  potassium  and  sodium,  10,  13. 

"  ammonium,  11. 

Calcium  from  potassium  and  sodium,  10,  14. 

ammonium,  11. 

Magnesium  from  potassium  and  sodium,  15-18. 
"  ammonium,  11. 

A.   General  Method. 

1.     THE    WHOLE    OF    THE    ALKALI-EARTH    METALS    FROM    Po- 
TASSIUM  AND  SODIUM. 

Principle  on  which  the  method  is  based  :  Ammonium  car-  10 
donate  precipitates,  from   a   solution  containing  ammonium 
chloride,  only  barium,  strontium,  and  calcium. 

Mix  the  solution,  in  which  the  metals  are  assumed  to  be 
contained  in  the  form  of  chlorides,  with  a  sufficient  quantity  of 

*  Annal.  d.  Chem.  u.  Pharm.  122,348.      f  Pogg.  Annal.  104,  102. 


§  153]  BASES   OF   GROUP   II.  489 

ammonium  chloride  to  prevent  the  precipitation  of  the  magne- 
sium by  ammonia ;  dilute  rather  considerably,  add  some  ammo- 
nia, then  ammonium  carbonate  in  slight  excess,  let  the  mixture 
stand  covered  for  an  hour  in  a  moderately  warm  place,  filter, 
and  wash  the  precipitate  with  water  to  which  a  few  drops  of 
ammonia  have  been  added. 

The  precipitate  contains  the  barium,  strontium,  and  cal- 
cium /  the  filtrate  the  magnesium  and  the  alkalies.  So  at 
least  we  may  assume  in  cases  where  the  highest  degree  of 
accuracy  is  not  required.  Strictly  speaking,  however,  the 
solution  still  contains  exceedingly  minute  traces  of  calcium 
and  somewhat  more  considerable  traces  of  barium,  as  the  car- 
bonates of  these  two  metals  are  not  absolutely  insoluble  in 
a  fluid  containing  ammonium  chloride;  the  precipitate  also 
may  contain  possibly  a  little  ammonium  magnesium  carbonate. 
Treat  the  precipitate  according  to  §  154,  and  the  filtrate — in 
rigorous  analyses — as  follows  :  Add  3  or  4  drops  (but  not  much 
more)  of  dilute  sulphuric  acid,  then  ammonium  oxalate,  and 
let  the  fluid  stand  again  for  12  hours  in  a  warm  place.  If  a 
precipitate  forms,  collect  this  on  a  small  filter,  wash,  and  treat 
on  the  filter  with  some  dilute  hydrochloric  acid,  which  dis- 
solves the  calcium  oxalate,  and  leaves  the  barium  sulphate 
undissolved.  Since  a  little  magnesium  oxalate  may  have  sepa- 
rated with  the  former,  add  some  ammonia  to  the  hydrochloric 
solution,  filter  after  the  precipitate  has  settled,  and  mix  the 
filtrate  with  the  principal  filtrate. 

Evaporate  the  fluid  containing  the  magnesium  and  the  alka- 
lies to  dryness,  and  remove  the  ammonium  salts  by  gentle  igni- 
tion in  a  covered  crucible,  or  in  a  small  covered  dish  of  platinum 
or  porcelain.*  In  the  residue,  separate  the  magnesium  from 
the  alkalies  by  one  of  the  methods  given  15 — 18. 

2.  THE  WHOLE  OF  THE  ALKALI-EARTH  METALS  FROM  AM-  11 
MONITJM. — The  same  principle  and  the  same  process  as  in  the 
separation  of  potassium  and  sodium  from  ammonium  (4  and  5). 


*  This  operation  effects  also  the  removal  of  the  small  quantity  of  sulphuric 
acid  added  to  precipitate  the  traces  of  barium,  as  sulphates  of  the  alkalies  are 
converted  into  chlorides  upon  ignition  in  presence  of  a  large  proportion  of 
ammonium  chloride. 


490  SEPARATION.  [§  153. 

B.  Special  Methods. 

SINGLE  ALKALI-EARTH  METALS  FROM  POTASSIUM  AND  SO- 
DIUM. 

1.  BARIUM  FROM  POTASSIUM  AND  SODIUM. 

Precipitate  the  barium  with  dilute  sulphuric  acid  (§  101, 1,  a),  12 
evaporate  the  filtrate  to  dryness,  and  ignite  the  residue,  with 
addition  towards  the  end  of  ammonium  carbonate  (§  97,  1  and 
§  98,  1).  Take  care  to  add  a  sufficient  quantity  of  sulphuric 
acid  to  convert  the  alkalies  also  completely  into  sulphates.  In 
exact  analyses,  in  order  to  save  the  alkali  salts  adhering  to  the 
barium  sulphate,  remove  the  dry  barium  sulphate  from  the 
filter,  heat  it  with  a  sufficient  quantity  of  pure  strong  sulphu- 
ric acid  to  dissolve  it  completely,  allow  to  cool,  dilute  largely, 
collect  the  barium  sulphate  (now  almost  absolutely  pure)  on  the 
first  filter,  ignite,  and  weigh.  Evaporate  the  filtrate  in  a  plati- 
num dish,  drive  off  the  sulphuric  acid,  and  estimate  the  traces 
of  the  alkalies. 

This  method  is,  on  account  of  its  greater  accuracy,  prefer- 
able to  the  one  in  A,  in  cases  where  the  barium  has  to  be  sepa- 
rated only  from  one  of  the  two  fixed  alkalies ;  but  if  both  alka- 
lies are  present,  the  other  method  is  more  convenient,  since  the 
alkalies  are  then  obtained  as  chlorides. 

2.  STRONTIUM  FROM  POTASSIUM  AND  SODIUM. 

Strontium  may  be  separated  from  the  alkalies  like  barium,  13 
by  means  of  sulphuric  acid ;  but  this  method  is  not  preferable 
to  the  one  in  10,  in  cases  where  the  choice  is  permitted  (comp. 
§  102). 

3.  CALCIUM  FROM  POTASSIUM  AND  SODIUM. 

Precipitate  the  calcium  with  ammonium  oxalate  (§  103,  2,  14 
Z>,  a),  evaporate  the  filtrate  to  dryness,  and  determine  the  alka- 
lies in  the  ignited  residue.  In  determining  the  alkalies,  dis- 
solve the  residue,  freed  by  ignition  from  the  ammonium  salts, 
in  water,  filter  if  necessary,  acidify  the  filtrate,  according  to  cir- 
cumstances, with  hydrochloric  acid  or  sulphuric  acid,  and  then 
evaporate  to  dryness ;  this  treatment  of  the  residue  is  neces- 
sary, because  ammonium  oxalate  partially  decomposes  chlorides 
of  the  alkali  metals  upon  ignition  with  formation  of  alkali  car- 
bonates, except  in  presence  of  a  large  proportion  of  ammonium 


§  153.]  BASES   OF   GROUP   II.  491 

chloride.  The  results  are  still  more  accurate  than  in  A,  except 
where  ammonium  oxalate  has  been  used,  after  the  precipitation 
by  ammonium  carbonate,  to  remove  the  minute  traces  of  lime 
from  the  filtrate. 

4.  MAGNESIUM  FROM  POTASSIUM  AND  SODIUM.* 

a.  Methods  based  upon  the  sparing  solubility  of  Magnesium 
Hydroxide  in  Water. 

a.  Make  the  solution  as  neutral  as  possible,  and  free  from  15 
ammonium  salts  (it  is  a  matter  of  indifference  whether  the  mag- 
nesium and  alkali  metals  are  present  as  sulphates,  chlorides,  or 
nitrates),  add  baryta-water  as  long  as  a  precipitate  forms,  heat 
to  boiling,  filter,  and  wash  the  precipitate  with  boiling  water. 
The  precipitate  contains  the  magnesium  as  hydroxide.  Dis- 
solve it  in  hydrochloric  acid,  precipitate  the  barium  with  sul- 
phuric acid,  and  then  the  magnesium  as  ammonium-magnesium 
phosphate  (§  104,  2).  The  alkalies,  which  are  contained  in  the 
solution,  according  to  circumstances,  as  chlorides,  nitrates,  or 
caustic  alkalies,  are  separated  from  the  barium  as  directed  in 
10  or  12.  LIEBIG,  who  wTas  tjie  first  to  employ  this  method, 
proposes  crystallized  barium  sulphide  as  precipitant.  The 
method  is  not  very  exact,  as  magnesium  is  somewhat  more 
soluble  in  solutions  of  alkali  salts  than  in  water.  On  this 
account  the  weighed  alkali  salt  must  always  be  tested  for 
magnesium,  and  the  latter  determined  if  required. 

fi.  Precipitate  the  solution  with  a  little  pure  milk  of  lime,  16 
boil,  filter,  and  wash.  Separate  the  calcium  and  magnesium  in 
the  precipitate  according  to  24 ;  the  calcium  and  the  alkalies  in 
the  filtrate  according  to  10  or  14.  This  method  may  be  em- 
ployed when  magnesium  has  to  be  removed  from  a  fluid  con- 
taining calcium  and  alkalies,  provided  the  alkalies  alone  are 
to  be  determined.  Minute  quantities  of  magnesium  also  in  this 
case  remain  with  the  alkali  salt  from  the  cause  mentioned  in  a. 

y.  Evaporate  the  solution  of  the   chlorides  (which  must  17 
contain  no  other  acids)  to  dryness,  and  if  ammonium  chloride 
is  present,  ignite ;  warm  the  residue  with  a  little  water  (this 
will  dissolve  it  with  the  exception  of  some  magnesium  oxide, 
which  separates).     Add  mercuric  oxide  shaken  up  with  water, 

*  The  methods  a,   a  and  ft,  are  suitable  for  the  separation  of  magnesium 
from  lithium. 


492  SEPARATION.  [§  153. 

evaporate  to  dryness  on  the  water-bath  with  frequent  stirring, 
dry  thoroughly,  ignite  with  increasing  temperature  till  all  the 
resulting  mercuric  chloride  is  volatilized.  (Avoid  inhaling  the 
fumes.)  There  is  no  need  to  continue  the  ignition  until  the 
whole  of  the  mercuric  oxide  is  expelled ;  on  the  contrary,  part 
of  it  may  be  filtered  off  together  with  the  magnesium  oxide, 
and  subsequently  volatilized  upon  the  ignition  of  the  latter. 
Treat  the  residue  with  small  quantities  of  hot  water,  filter  off 
rapidly,  and  wash  the  magnesium  oxide  with  hot  water,  using 
small  quantities  at  a  time,  and  not  continuing  the  operation 
unnecessarily.  The  solution  contains  the  alkalies  in  form  of 
chlorides.  This  method,  proposed  by  BERZELIUS,  gives  satis- 
factory results,  and,  as  far  as  my  experience  goes,  is  the  best  of 
those  given  under  a.  Take  care  to  add  the  mercuric  oxide  only 
in  proper  quantity,  and  always  test  the  alkali  chlorides  for  mag- 
nesium, a  trace  of  which  will  generally  be  found. 

1).  Method  based  on  the  Precipitation  of  the  Magnesium 
as  Ammonium  Magnesium  Carbonate. 

Mix  the  solution  of  sulphates,  nitrates,  or  chlorides  (it  must  18 
be  very  concentrated)  with  an  excess  of  a  concentrated  solution 
of  sesquicarbonate  of  ammonia  in  water  and  ammonia  (230  grm. 
of  the  salt,  360  c.c.  solution  of  ammonia  sp.  gr.  -96,  and  water 
to  1  litre).  After  twenty-four  hours  filter  off  the  precipitate 
(MgCO3- (NH4)2CO3+ 4H2O),  wash  it  with  the  solution  of  am- 
monia and  ammonium  carbonate  used  for  the  precipitation,  dry, 
ignite  strongly  and  for  a  sufncienfrlength  of  time,  and  weigh  the 
magnesium  oxide.  Evaporate  the  filtrate  to  dryness  (keeping 
the  heat  at  first  under  100°,  expel  the  ammonium  salts,  and  de- 
termine the  alkalies  as  chlorides  or  sulphates.  When  sodium 
alone  is  present  the  results  are  tolerably  satisfactory.  In  the 
presence  of  potassium  the  ignited  magnesium  oxide  must  be 
extracted  with  water,  before  weighing,  as  it  contains  an  appre- 
ciable quantity  of  potassium  carbonate ;  the  washings  are  to  be 
added  to  the  principal  filtrate.  This  last  measure  is  unneces- 
sary in  the  absence  of  potassium.  The  magnesium  is  always  a 
little  too  low.  Mean  error  y^Vo  (F.  G.  SCHAFFGOTSCH,*  H. 
WEBER  f). 


*  Pogg.  Annal.  104,  482.  f  Vierteljahresschrift  f.  prakt.  Pharm.  8,  161. 


§  154.]  BASES    OF   GROUP   II.  493 

II.  SEPARATION  OF  THE  BASIC  RADICALS  OF  THE  SECOND 

GROUP    FROM    EACH    OTHER. 

§154. 

INDEX.    (The  numbers  icfer  to  those  in  the  margin.) 

Barium  from  strontium,  20,  23,  32. 

calcium,  22,  23,  27,  32. 
"        magnesium,  19,  21. 
Strontium  from  barium,  20,  23,  32. 
calcium,  26,  30,  31. 
magnesium,  19,  21. 

Calcium  from  barium,  20,  22,  23,  27,  32. 
strontium,  26,  30,  31 
magnesium,  19,  24,  25,  28,  29. 
Magnesium  from  barium,  19,  21. 

strontium,  19,  21. 
calcium,  19,  24,  25,  28,  29. 

A.  General  Method. 

THE     WHOLE     OF     THE     ALKALI-EARTH    METALS    FROM    EACH 
OTHER. 

Proceed  as  in  10.  The  magnesium  is  precipitated  from  the  19 
filtrate  as  ammonium  magnesium  phosphate.  The  precipitated 
carbonates  of  barium,  strontium,  and  calcium  are  dissolved  in 
hydrochloric  acid,  and  the  bases  separated  as  directed  in  20. 
The  traces  of  magnesium,  which  may  be  present  in  the  ammo- 
nium carbonate  precipitate,  are  obtained  by  evaporating  the  fil- 
trate from  the  strontium  or  calcium  sulphate  to  dryness,  taking 
up  the  residue  with  water,  and  precipitating  the  solution  with 
sodium  phosphate  and  ammonia. 

B.  Special  Methods. 

1.  Methods  based  upon  the  Insolubility  of  Barium 
Silicqfluoride. 

BARIUM  FROM  STRONTIUM  AND  FROM  CALCIUM. 

Mix  the  neutral  or  slightly  acid  solution  with  hydrofluosili-  20 
cic  acid*  in  excess,  add  one  third  of  the  volume  of  alcohol  of 
•81  sp.  gr.,  let  the  mixture  stand  twelve  hours,  collect  the  pre- 
cipitate of  barium  silicofluoride  on  a  weighed  filter,  wash  with 

*  If  not  kept  in  a  gutta-percha  bottle  it  should  be  freshly  prepared. 


494  SEPARATION.  [§  154. 

a  mixture  of  equal  parts  of  water  and  alcohol  until  the  wash- 
ings cease  to  show  even  the  least  trace  of  acid  reaction  (but  no 
longer),  and  dry  at  100°.  Precipitate  the  strontium  or  calcium 
from  the  filtrate  by  dilute  sulphuric  acid  (§  102,  1,  a,  and  §  103, 
1).  The  results  are  satisfactory.  For  the  properties  of  barium 
silicofluoride,  see  §  71.  If  both  strontium  and  calcium  are  pres- 
ent, the  sulphates  are  weighed,  and  then  separated  according 
to  26,  or  they  are  converted  into  carbonates  (§  132,  II,,  b),  and 
separated  according  to  31  or  30. 

2.  Methods  based  upon  the  Insolubility  of  Barium 
Sulphate  or  Strontium  Sulphate,  as  the  case  may  be,  in 
Water  and  in  Solution  of  Sodium  T hiosulphate. 

a.  BARIUM  AND  STRONTIUM  FROM  MAGNESIUM. 

Precipitate  the  barium  and  strontium  with  sulphuric  acid  21 
(§  101,  1,  a  and  §  102,  1,  a\  and  the  magnesium  from  the  fil-_ 
trate    with    ammonia     and     sodium     ammonium     phosphate 
(§  104,  2). 

b.  BARIUM  FROM  CALCIUM. 

Mix  the  solution  with  hydrochloric  acid,  then  with  highly  22 
dilute  sulphuric  acid  (1  part  acid  to  300  water),  as  long  as  a  pre- 
cipitate forms  ;  allow  to  deposit,  and  determine  the  barium  sul- 
phate as  directed  §  101,  1,  a.  Concentrate  the  washings  by 
evaporation  and  add  them  to  the  filtrate,  neutralize  the  acid 
with  ammonia,  and  precipitate  the  calcium  as  oxalate  (§  103,  2, 
b,  a).  The  method  is  principally  to  be  recommended  when 
small  quantities  of  barium  have  to  be  separated  from  much  cal- 
cium. If  we  have  to  separate  calcium  sulphate  from  barium 
sulphate,  the  salts  may  (in  the  absence  of  free  acids)  be  treated 
repeatedly  with  a  solution  of  sodium  thiosulphate  at  a  gentle 
heat.  The  barium  sulphate  remains  undissolved,  the  calcium 
sulphate  dissolves.  The  calcium  is  precipitated  from  the  fil- 
trate by  ammonium  oxalate  (DIEHL*). 

3.  Method  based  upon  the  different  deportment  with 
Alkali  Carbonates  of  Barium  Sulphate  on  the  one  hand, 
and  Strontium  and  Calcium  Sulphates  on  the  other. 

BARIUM  FROM  STRONTIUM  AND  CALCIUM. 

Digest  the  three  precipitated  sulphates  for  twelve  hours  at  23 
*  Journ.  f.  prakt.  Chem.  79,  430. 


§  154.]  BASES    OF   GROUP   II.  495 

the  common  temperature  (15° — 20°),  with  frequent  stirring, 
with  a  solution  of  ammonium  carbonate,  decant  the  fluid  on  to 
a  filter,  treat  the  residue  repeatedly  in  the  same  way.  wash 
finally  with  water,  and  in  the  still  moist  precipitate,  separate 
the  undecomposed  barium  sulphate  by  means  of  cold  dilute 
hydrochloric  acid  from  the  strontium  and  calcium  carbonates 
formed.  To  hasten  the  separation  you  may  boil  the  sulphates 
for  some  time  with  a  solution  of  potassium  (not  sodium)  car- 
bonate, to  which  ^  the  amount  of  the  carbonate,  or  more,  of 
potassium  sulphate  has  been  added.  By  this'  process,  also,  the 
strontium  and  calcium  sulphates  are  decomposed,  the  barium 
sulphate  remaining  unacted  on.  If  the  basic  metals  are  in  solu- 
tion, the  above  solution  of  potassium  carbonate  and  sulphate  is 
added  in  excess  at  once,  and  the  whole  boiled.  The  precipitate, 
consisting  of  barium  sulphate  and  strontium  and  calcium  car- 
bonates, is  to  be  treated  as  above  with  cold  hydrochloric  acid 
(H.  ROSE*). 

4.  Methods  based  on  the  Insolubility  of  Calcium  /Sul- 
phate m  Alcohol. 

CALCIUM  FROM  MAGNESIUM. 

a.  Remove  water  and  free  hydrochloric  from  a  solution  of  24 
the  chlorides  by  evaporation,  dissolve  the  residue  in  strong  (but 
not  absolute)  alcohol,  add  a  slight  excess  of  pure  strong  sulphu- 
ric acid,  digest  in  the  cold,  allow  to  stand  for  some  hours,  trans- 
fer the  precipitate   consisting  of  calcium  sulphate  and  some 
magnesium  sulphate  to  a  filter,  wash  away  the  acid  thoroughly 
with  nearly  absolute  alcohol,  and  then  continue  the  washing 
with  alcohol  sp.  gr.  *96 — '95  till  a  few  drops  of  the  washings 
give  no  residue  on  evaporation.    Weigh  the  calcium  sulphate 
according  to  §  103,  1.     Evaporate  the  alcohol  from  the  filtrate, 
and  determine  the  magnesium  according   to  §  104,   2.     The 
method  is  in  itself  not  new,  but  A.  CmzYNSKi,t  adopting  the 
precautions  here  given,  has  obtained  excellent  results,  even  in 
the  presence  of  phosphoric  acid. 

b.  SMALL  QUANTITIES  OF  CALCIUM  FROM  MUCH  MAGNESIUM.  25 
Convert  into  neutral  sulphates,  dissolve  the  mass  in  water,  and 
add  alcohol,  with  constant  stirring,  till  a  slight  permanent  tur- 


Pogg.  Annal.  95,  286,  299,  427.  f  Zeitschr.  f.  anal.  Chem.  4,  348. 


496  SEPARATION.  [§  154. 

bidity  is  produced,  Wait  a  few  hours  and  then  filter,  wash  the 
precipitated  calcium  sulphate  with  alcohol  which  has  been 
diluted  with  an  equal  volume  of  water,  and  determine  it  after 
§  103,  1,  a  (in  which  case  the  weighed  sulphate  must  be  tested 
for  magnesium),  or  dissolve  the  precipitate  in  water  containing 
hydrochloric  acid  and  separate  the  calcium  from  the  small  quan- 
tity of  magnesium  possibly  coprecipitated  according  to  28 

(SCHEERER*). 

5.  Methods  based  on  the  Insolubility  of  Strontium  and 
Barium  Sulphates  in  solution  of  Ammonium  Sulphate. 

STRONTIUM  FKOM  CALCIUM. 

If  the  mixture  is  soluble,  dissolve  in  the  smallest  quantity  26 
of  water,  add  about  50  times  the  quantity  of  the  substance  of 
ammonium  sulphate  dissolved  in  four  times  its  weight  of  water, 
and  either  boil  for  some  time  with  renewal  of  the  water  that 
evaporates  and  addition  of  a  very  little  ammonia  (as  the  solu- 
tion of  ammonium  sulphate  becomes  acid  on  boiling),  or  allow  to 
stand  at  the  ordinary  temperature  for  twelve  hours.  Filter  and 
wash  the  precipitate,  which  consists  of  strontium  sulphate  and 
a  little  ammonium  strontium  sulphate,  with  a  concentrated  solu- 
tion of  ammonium  sulphate,  till  the  washings  remain  clear  on 
addition  of  ammonium  oxalate.  The  precipitate  is  cautiously 
ignited,  moistened  with  a  little  dilute  sulphuric  acid  (to  convert 
the  small  quantity  of  strontium  sulphide  into  sulphate),  reig- 
nited  and  weighed.  The  highly  dilute  filtrate  is  precipitated 
with  ammonium  oxalate,  and  the  calcium  determined  according 
to  §  103,  2,  J,  a.  If  you  have  the  solid  sulphates  to  analyze, 
they  are  very  finely  powdered  and  boiled  with  concentrated  solu- 
tion of  ammonium  sulphate  with  renewal  of  the  evaporated 
water  and  addition  of  a  little  ammonia.  Results  very  close,  e.g., 
1-048  Sr(lSrO3)2  instead  of  .1-053,  and  -497  CaC03,  instead  of  -504 
(H.  RosEj). 

BARIUM  may  be  separated  FROM  CALCIUM  in  the  same  way.     27 

6.  Methods  based  upon  the  Insolubility  of  Calcium 
Oxalate  in  Ammonium  Chloride  and  in  Acetic  Acid. 

CALCIUM  FROM  MAGNESIUM. 

a.  Mix  the  properly  diluted  solution  with  sufficient  ammo-  28 

*  Annal.  d.  Chem.  u.  Pharm.  110,  237.  $  Pogg.  Annal.  110,  296. 


§  154.]  BASES   OF   GROUP   II.  497 

nium  chloride  to  prevent  the.  formation  of  a  precipitate  by 
ammonia,  which  is  added  in  slight  excess ;  add  ammonium  oxa- 
late  as  long  as  a  precipitate  forms,  then  a  further  portion  of  the 
same  reagent,  about  sufficient  to  convert  the  magnesium  also 
into  oxalate  (which  remains  in  solution).  This  excess  is  abso- 
lutely indispensable  to  insure  complete  precipitation  of  the  cal- 
cium, as  calcium  oxalate  is  slightly  soluble  in  magnesium  chlo- 
ride not  mixed  with  ammonium  oxalate  (Expt.  Xo.  92).  Let 
the  mixture  stand  twelve  hours,  decant  the  supernatant  clear 
fluid,  as  far  as  practicable,  from  the  precipitated  calcium  oxa- 
late, mixed  with  a  little  magnesium  oxalate,  on  to  a  filter,  wash 
the  precipitate  once  in  the  same  way  by  decantation,  then  dis- 
solve in  hydrochloric  acid,  add  water,  then  ammonia  in  slight 
excess,  and  a  little  ammonium  oxalate.  Let  the  fluid  stand 
until  the  precipitate  has  completely  subsided,  then  pour  on  to 
the  previous  filter,  transfer  the  precipitate  finally  to  the  latter, 
and  proceed  exactly  as  directed  §  103,  2,  5,  a.  The  first  filtrate 
contains  by  far  the  larger  portion  of  the  magnesium,  the  second 
the  remainder.  Evaporate  the  second  filtrate,  acidified  with 
hydrochloric  acid,  to  a  small  volume,  then  mix  the  two  fluids, 
and  precipitate  the  magnesium  with  sodium  ammonium  phos- 
phate (HXaXH4)PO4 ,*as  directed  §  104,  2.  If  the  quantity  of 
ammonium  salts  present  is  considerable,  the  estimation  of  the 
magnesium  is  rendered  more  accurate  by  evaporating  the  fluids 
in  a  large  platinum  or  porcelain  dish  to  dryness,  and  igniting 
the  residuary  saline  mass,  in  small  portions  at  a  time,  in  a  smaller 
.platinum  dish,  until  the  ammonium  salts  are  expelled.  The 
residue  is  then  treated  with  hydrochloric  acid  and  water, 
warmed,  allowed  to  cool,  and  rendered  just  alkaline  with  ammo- 
nia. If  enough  ammonium  chloride  is  present,  no  magnesium 
hydroxide  will  fall  down,  but  occasionally  small  flocks  of  silica 
or  alumina  are  to  be  seen.  Filter  them  off  and  finally  precipi- 
tate with  ammonia  and  (KN~aKH4)PO4.  If  the  precipitate  pro- 
duced by  ammonia  is  at  all  considerable,  dissolve  it  in  hydro- 
chloric acid,  evaporate  the  solution  on  a  water-bath  to  dryness, 
treat  the  residue  with  hydrochloric  acid  and  water,  render  alka- 
line with  ammonia,  filter,  and  add  the  filtrate  to  the  principal 
solution. 


*  This  is  preferable  to  sodium  phosphate  as  a  precipitant,  see  MOKR,  Zeitschr. 
f.  anal.  Chem.  12,  36. 


498  SEPARATION.  [§  154. 

Numerous  experiments  have  convinced  me  that  this  method, 
which  is  so  frequently  employed,  gives  accurate  results  only  if 
the  foregoing  instructions  are  strictly  complied  with.  It  is  only 
in  cases  where  the  quantity  of  magnesium  present  is  relatively 
small  that  a  single  precipitation  with  ammonium  oxalate  may 
be  found  sufficient  (comp.  Expt.  No.  93*). 

Z>.  In  the  case  of  calcium  and  magnesium  phosphates,  dis-  29 
solve  in  the  least  possible  quantity  of  hydrochloric  acid,  add 
ammonia  until  a  copious  precipitate  forms ;  redissolve  this  by 
addition  of  acetic  acid,  and  precipitate  the  calcium  with  an 
excess  of  ammonium  oxalate.  To  determine  the  magnesium, 
precipitate  the  nitrate  with  ammonia  and  (HNaNH4)PO4.  As 
free  acetic  acid  by  no  means  prevents  the  precipitation  of  small 
quantities  of  magnesium  oxalate,  the  precipitate  contains  some 
magnesium,  and  as  calcium  oxalate  is  not  quite  insoluble  in 
acetic  acid,  the  nitrate  contains  some  calcium ;  these  two  sources 
of  error  compensate  each  other  in  some  measure.  In  accurate 
analysis,  however,  these  trifling  admixtures  of  magnesium  and 
calcium  are  afterwards  separated  from  the  weighed  precipi- 
tates of  calcium  carbonate  or  oxide  and  magnesium  pyrophos- 
phate  respectively. 

7.  Method  based  upon  the  Insolubility  of  Strontium 
Nitrate  in  Alcohol  and  Ether. 

STRONTIUM  FROM  CALCIUM  (after  STROMEYER). 

Digest  the  perfectly  dry  nitrates  in  a  closed  flask  with  abso-  30 
lute  alcohol,  to  which  an  equal  volume  of  ether  should  be  added 
(H.  ROSE).  Filter  off  the  undissolved  strontium  nitrate  in  a 
covered  funnel,  wash  with  the  mixture  of  alcohol  and  ether,  dis- 
solve in  water,  and  determine  as  strontium  sulphate  (§  102,  1). 
Precipitate  the  calcium  from  the  filtrate  by  sulphuric  acid. 
The  results  are  satisfactory. 

8.  Indirect  Method. 
STRONTIUM  FROM  CALCIUM. 

Determine  both  bases  first  as  carbonates  or  oxides,  precipi-  31 

*  Further  experiments  will  be  found  in  Zeitschr.  f .  anal.  Chem.  7,  310.  Com- 
pare also  WITTSTEIN,  Zeitschr.  f.  anal.  Chem.  2,  318,  and  COSSA,  Ib.  8,  141. 
According  to  HAGER,  Ib.  9,  254,  the  precipitate  of  calcium  oxalate  will  be  free 
from  magnesium  if  filtered  off  immediately  ;  however,  I  fear  that  a  little  calcium 
might  in  this  case  be  left  in  solution. 


§  154.]  BASES    OF    GROUP   III.  499 

fating  them  either  with  ammonium  carbonate  or  oxalate  (§§  102, 
103) ;  then  estimate  the  amount  of  carbonic  acid  in  them,  and 
calculate  the  amount  of  strontium  and  calcium  as  directed  in 
"  Calculation  of  Analyses."  The  determination  of  the  carbonic 
acid  may  be  effected  by  fusion  with  vitrified  borax  (§  139,  II.,  <?), 
but  the  application  of  a  moderate  white  heat,  such  as  is  given 
by  a  good  gas  blowpipe  without  the  use  of  a  crucible  jacket,  is 
alone  sufficient  to  drive  out  all  the  carbonic  acid  from  both  the 
carbonates  (F.  G.  SCHAFFGOTSCH*).  I  can  strongly  recommend 
tliis  method.  It  is  well  to  precipitate  the  carbonates  hot,  to 
press  the  precipitate  cautiously  down  in  the  platinum  crucible 
and  turn  over  the  agglomerated  cake  every  now  and  then  till, 
after  repeated  ignitions,  the  weight  has  become  constant.  The 
results  are  good  if  neither  of  the  bases  is  present  in  too  minute 
quantity. 

The  indirect  separation  may,  of  course,  be  effected  by  means  32 
of  other  salts,  and  can  be  used  also  for  the  determination  of  CAL- 
CIUM    IN     PRESENCE    OF    BAKIUM  OF  of  BARIUM    IN    PRESENCE    OF 

STRONTIUM.  In  the  expulsion  of  carbonic  acid  from  barium  car- 
bonate vitrified  borax  must  be  used  (§  139,  II.,  c). 

Third  Group. 

ALUMINIUM CHROMIUM. 

I.  SEPARATION  OF  ALUMINIUM  AND   CHROMIUM  FROM  THE 

ALKALIES. 

§155. 
1.  FROM  AMMONIUM. 

a.  Aluminium  and  chromium  salts  may  oe  separated  from  33 
ammonium  salts  by  ignition.     However,  in  the  case  of  alu- 
minium, this  method  is  applicable  only  in  the  absence  of  chlo- 
rine (volatilization  of  aluminium  chloride).     The  safest  way, 
therefore,  is  to  mix    the   compound   with    sodium   carbonate 
before  igniting. 

b.  Determine  the  ammonium  by  one  of  the  methods  given  34 
in  §  99,  3,  using  solution  of  potassa  or  soda  to  effect  the  expul- 
sion of  ammonia.     The  aluminium  and  chromium  are  then 
determined  in  the  residue  in  the  same  way  as  in  35. 

*  Pogg.  Annal.  113,  615. 


500  SEPARATION.  [§  156. 

2.  FROM  POTASSIUM  AND  SODIUM. 

a  Precipitate  and  determine  the  chromium  and  aluminium  35 
with  ammonia  as  directed  in  §  105,  a,  and  §  106,  1,  a.  The  ni- 
trate contains  the  alkalies,  which  are  then  freed  from  the  ammo- 
nium salt  formed,  by  evaporation  to  dryness  and  ignition.  In 
the  presence  of  large  quantities  of  alkali  salts  it  is  well  to  dis- 
solve the  moderately  ignited  precipitate  in  hydrochloric  acid, 
and  reprecipitate  with  ammonia. 

b.  Aluminium  may  be  separated  also  from  potassium  and  36 
sodium  by  heating  the  nitrate  (see  38). 

II.  SEPARATION  OF  ALUMINIUM  AND  CHROMIUM  FROM  THE 
ALKALI-EARTH  METALS. 

§156. 

INDEX.     (The  numbers  refer  to  those  in  the  margin.) 

Aluminium  from  barium,  37 — 41,  and  43. 

'•          strontium,  37 — 41,  and  43. 

calcium,  37 — 41,  and  44,  46. 
"          magnesium,  37 — 41,  and  46, 
Chromium  from  the  alkali-earth  metals,  47 — 50. 

SEPARATION  OF  ALUMINIUM  FROM  THE  ALKALI-EARTH  METALS. 
A.   General  Methods. 

THE    WHOLE     OF     THE    ALKALI-EARTH     METALS    FROM    ALU- 
MINIUM. 

1.  Method  based  upon  the  Precipitation  of  Alu- 
minium Hydroxide  by  Ammonia,  and  upon  its  solution 
in  Soda. 

Put  the  solution  in  a  platinum  dish  or,  with  less  advantage,  37 
a  porcelain  dish.  Let  it  be  dilute  and  warm.  •  Add  a  tolerable 
quantity  of  ammonium  chloride,  if  such  be  not  already  present, 
then  very  gradually,  almost  drop  by  drop  (WRINKLE*),  ammo- 
nia as  free  as  possible  from  carbonic  acid,  in  moderate  excess, 
and  boil  till  no  more  free  ammonia  is  observable.  Under  these 
circumstances,  a  little  magnesium  hydroxide,  and  also  a  small 
quantity  of  calcium,  barium,  or  strontium  carbonates  are  at  first 
precipitated  along  with  the  aluminium  hydroxide ;  on  the  boil- 

*  Zeitschr.  f.  anal.  Chem.  10,  96. 


§  156.]  BASES   OF   GEOUP   III.  5()1 

ing  with  ammonium  chloride,  the  coprecipitated  alkali-earth 
metal  compounds  redissolve,  so  that  the  aluminium  hydroxide 
finally  retains  only  an  unweighable  or  scarcely  weighable  trace 
of  them.  Allow  to  deposit,  and  proceed  with  the  aluminium 
'determination  according  to  §  105,  a.  In  very  exact  analysis  it 
is  well,  after  moderately  washing  the  aluminium  precipitate,  to 
redissolve  it  in  hydrochloric  acid,  and  reprecipitate  with  ammo- 
nia as  above.  In  separations  of  aluminium  from  calcium  or 
magnesium  this  double  precipitation  is  especially  necessary  in 
the  presence  of  sulphates.  After  the  aluminium  oxide  has 
been  weighed,  fuse  it  for  a  long  time  with  potassium  disul- 
phate,  dissolve  the  fused  mass  in  water,  and  determine  any  sili- 
cic acid*  that  may  remain.  The  solution,  when  mixed  with 
potassa  in  excess,  will  often  not  appear  perfectly  clear,  but  will 
contain  a  few  flocks  of  magnesium  hydroxide  (perhaps  also 
traces  of  barium,  strontium,  or  calcium  carbonates).  If  there  is 
any  amount  of  the  latter,  filter  it  off,  dissolve  in  nitric  acid,  pre- 
cipitate with  ammonia,  boil  till  the  fluid  ceases  to  smell  of 
ammonia,  filter,  evaporate  the  small  quantity  of  fluid  in  a  pla- 
tinum capsule,  ignite,  weigh  the  residual  magnesium  oxide 
( which  may  contain  traces  of  other  alkali-earth  metals),  deduct 
it  from  the  aluminium  oxide,  dissolve  it  in  hydrochloric  acid, 
and  add  to  the  original  filtrate.  In  order  to  the  further  separa- 
tion of  the  alkali-earth  metals,  acidify  the  fluid  containing  them 
with  hydrochloric  acid,  evaporate  (preferably  in  a  platinum  dish) 
to  a  small  bulk,  and  while  still  warm  add  ammonia  just  in 
excess.  A  small  precipitate  of  aluminium  hydroxide  is  some- 
times formed  at  this  stage ;  filter  off,  wash,  and  weigh  with  the 
principal  precipitate.  In  the  filtrate  determine  the  alkali-earth. 
metals  according  to  §  154. 

[The  difficulty  of  washing  aluminium  hydroxide  usually 
increases  with  lapse  of  time  between  precipitation  and  filtra- 
tion. This  difficulty  may  be  to  some  extent  obviated  by  the 
following  slight  modification  of  the  above-described  manipula- 
tion. Add  ammonia  to  the  solution,  which  may  occupy  a  vol- 
ume of  400  c.c.  for  *2  gr.  A12O3,  until  free  acid  is  partially  neu- 
tralized, but  not  until  a  permanent  precipitate  is  formed ;  add 


*  A  small  quantity  will  always  be  found  if  you  have  boiled  in  a  glass  or 
porcelain  vessel. 


502  SEPARATION.  [§  156. 

also  ammonium  chloride  if  but  little  free  acid  was  present.  Heat 
nearly  to  boiling,  and  add  ammonia  slowly  until  a  permanent 
precipitate  begins  to  form,  then  drop  by  drop  until  a  slip  of  red 
litmus-paper  dipped  into  the  fluid  changes  to  blue  and  the  odor 
of  ammonia  becomes  perceptible  on  boiling.  Carefully  avoid 
the  use  of  more  ammonia  than  is  sufficient  to  produce  these 
indications  of  a  slight  excess.  Boil  rapidly  7  to  10  minutes, 
allow  the  precipitate  to  settle  5  to  10  minutes,  filter  and  wash 
the  precipitate  moderately  upon  the  filter.  Remove  the  filter 
with  the  moist  precipitate  from  the  funnel,  and  unfold  it  upon 
the  side  of  a  beaker  having  a  height  exceeding  the  diameter  of 
the  filter,  so  that  the  latter  may  not  extend  to  the  bottom 
of  the  bea,ker.  Rinse  the  precipitate  from  the  filter  down 
to  the  bottom  of  the  beaker  with  a  strong  jet  of  water 
and  dissolve  (completely  or  nearly)  by  adding  concentrated 
hydrochloric  acid.  Moisten  also  the  filter  with  acid  somewhat 
diluted,  and  rinse  the  small  amount  of  aluminium  chloride  solu- 
tion thus  formed  out  of  the  paper  with  a  jet  of  water.  Push 
up  the  filter  now,  if  necessary  with  a  rod,  so  that  it  may  be 
above  the  solution,  and  allow  it  to  remain  adhering  to  the  side 
of  the  beaker.  The  solution  need  not,  for  this  second  precipi- 
tation, occupy  a  volume  above  200 — 250  c.c.  Precipitate  the 
aluminium  precisely  as  before,  moistening  also  the  filter  with 
ammonia  solution.  Immediately  after  boiling  pour  the  solution 
with  the  precipitate  upon  a  filter.  Push  the  old  filter  down  to 
the  bottom  of  the  beaker,  wash  it  by  adding  and  decanting 
small  successive  portions  of  hot  water,  stirring  and  pressing  the 
paper  with  a  rod  and  pouring  the  water  upon  the  precipitate, 
until  a  few  drops  of  the  decanted  water  give  no  turbidity  with 
silver  nitrate.  Next  complete  the  washing  of  the  precipitate 
on  the  filter  with  hot  water.  After  the  washing  is  complete, 
beat  up  the  old  filter  in  the  beaker  with  a  glass  rod  and  rinse  it 
out  upon  the  top  of  the  washed  precipitate — the  old  filter  must 
on  no  account  be  thrown  away,  since  it  may  retain  a  little  alu- 
minium hydroxide  which  treatment  with  hydrochloric  acid 
failed  to  dissolve.  Add  to  the  united  filtrates  ammonia  to 
decided  alkaline  reaction  ;  heat  until  the  solution  becomes  neu- 
tral. If  more  aluminium  hydroxide  separates,  collect  it  on  a 
small  filter.] 


§  156.]  BASES   OF   GROUP   III.  503 

2.  Method  based  upon  the  unequal  Decomposdbility 
of  the  Nitrates  at  a  Moderate  Heat  (DEVILLE*). 

To  make  this  simple  and  convenient  method  applicable,  the  38 
basic  metals  must  be  present  as  pure  nitrates.  Evaporate  to  dry- 
ness  in  a  platinum  dish,  and  heat  gradually,  with  the  cover  on, 
in  the  sand-  or  air-bath — or,  better  still,  on  a  thick  iron  disk, 
with  two  cavities,  one  for  the  platinum  dish,  the  other,  filled 
with  brass  turnings,  for  inserting  a  thermometer — to  from 
200°  to  250°,  until  a  glass  rod  moistened  with  ammonia  ceases 
to  indicate  further  evolution  of  nitric-acid  fumes.  You  may 
also,  without  risk,  continue  to  heat  until  nitrous-acid  vapors  form. 
The  residue  consists  of  aluminium  oxide,  barium,  strontium  and 
calcium  nitrates,  and  normal  and  basic  magnesium  nitrates. 

Moisten  the  mass  with  a  concentrated  solution  of  ammonium 
nitrate,  and  heat  gently,  but  do  not  evaporate  to  dryness. 
Repeat  this  operation  until  no  further  evolution  of  ammo- 
nia is  perceptible.  (The  basic  magnesium  nitrate,  insoluble  in 
water,  dissolves  in  nitrate  of  ammonia,  with  evolution  of  ammo- 
nia, as  normal  magnesium  nitrate.)  Add  water,  and  digest  at 
a  gentle  heat. 

[If  the  ammonium  nitrate  has  evolved  only  imperceptible 
traces  of  ammonia,  pour  hot  water  into  the  dish,  stir,  and  add  a 
drop  of  dilute  ammonia  ;  this  must  cause  no  turbidity  in  the 
fluid  ;  should  the  fluid  become  turbid,  this  proves  that  the  heat- 
ing of  the  nitrates  has  not  been  continued  long  enough  ;  in 
which  case  you  must  again  evaporate  the  contents  of  the  dish, 
and  heat  once  more.] 

The  aluminium  oxide  remains  undissolved  in  the  form  of  a 
dense  granular  substance.  Decant  after  digestion,  and  wash  with 
boiling  water  ;  ignite  strongly  in  the  same  vessel  in  which  the 
separation  has  been  effected,  and  weigh.  Test  the  weighed  alu- 
minium oxide  according  to  37.  Separate  the  alkali-earth  metals 
as  directed  §  154. 

In  the  same  way  aluminium  may  be  separated  also  from 
potassium  and  sodium  (36.) 

3.  Method  in  which  the  processes  of  1  and  2  are  com- 
bined. 

Precipitate  the  aluminium  as  in  37,  wash  in  the  same  way  39 

*  Journ.  f.  prakt.  Chem.  1853,  60,  9. 


504  SEPARATION.  [§  156. 

as  there  directed,  then  treat,  while  still  moist,  with  nitric  acid, 
and  proceed  according  to  38,  to  remove  the  trifling  amount  of 
magnesium,  etc.,  coprecipitated  ;  add  the  solution  obtained  to 
the  principal  solution  of  the  alkaline  earths,  and  treat  the  fluid 
as  directed  in  37.  This  method  may  be  employed  also  in  the 
case  of  chlorides ;  it  will  be  sometimes  found  useful. 

4.  Method  based  upon   the   Precipitation  of  Alumin- 
ium by  Sodium  Acetate  or  Formate  upon  foiling. 

The  same  process  as  for  the  separation  of  ferric  iron  from  40 
the  alkali-earth  metals.  The  method  is  employed  more  par- 
ticularly when  both  aluminium  and  ferric  iron  have  to  be 
separated  from  alkali-earth  metals  at  the  same  time.  The 
precipitation  of  the  aluminium  is  usually  not  quite  complete, 
so  that  it  will  be  necessary  to  separate  the  aluminium  which 
remains  in  solution  from  the  filtrate  (37). 

5.  Method  based  on  the  Precipitation  of  Aluminium 
by  Ammonium  Succinate. 

Proceed  as  for  the  precipitation  of  ferric  iron  by  the  same  41 
reagent  (§  159);    especially  to  be  employed  when  aluminium 
and  ferric  iron  are  both  to  be  separated  from  alkali-earth  metals 
at  the  same  time.     The  filtrate  must  be  tested  according  to  40. 

B.  Special  Methods. 
SOME  OF  THE  ALKALI-EARTH  METALS  FROM  ALUMINIUM. 

1.  Methods  based  upon  the  Precipitation  of  some  of 
the  Salts  of  the  Alkali-earth  Metals. 

a.  BARIUM  AND  STRONTIUM  FROM  ALUMINIUM. 
Precipitate  the  barium  and  strontium  with  sulphuric  acid  43 

(§§  101  and  102),  and  the  aluminium  from  the  filtrate  as  directed 
§  105,  a.  This  method  is  especially  suited  for  the  separation  of 
barium  from  aluminium.  In  accurate  analyses  the  barium  sul- 
phate must  be  purified  according  to  12. 

b.  CALCIUM  FROM  ALUMINIUM. 

Add  ammonia  to  the  solution  until  a  permanent  precipitate  44 
forms,  then  acetic  acid  until  this  precipitate  is  redissolved,  then 
ammonium  acetate,  and  finally  ammonium   oxalate  in  slight 
excess  (§  103,  2,  5,  /?);  allow  the  precipitated  calcium  oxalate 


£  156.]  BASES   OF   GKOUP   III.  505 

to  deposit  in  the  cold,  then  filter,  and  precipitate  the  aluminium 
from  the  filtrate  as  directed  §  105,  a. 

2.  Method  based  upon  the  Precipitation  of  Alumi- 
nium by  Barium  Carbonate. 

ALUMINIUM  FROM  MAGNESIUM  AND  SMALL  QUANTITIES  OF 
CALCIUM. 

Mix  the  slightly  acid  dilute  fluid  in  a  flask,  with  a  moderate  46 
excess  of  barium  carbonate  shaken  up  with  water ;  cork  the 
flask  and  let  the  mixture  stand  in  the  cold  until  the  aluminium 
hydroxide  has  subsided,  wash  by  decantation  three  times,  filter, 
and  then  determine  the  aluminium  in  the  precipitate  as  directed 
43 ;  in  the  filtrate,  first  precipitate  the  barium  by  sulphuric 
acid  (22),  and  then  separate  the  calcium  and  magnesium  accord- 
ing to  §  154. 

SEPARATION  OF  CHROMIUM  FROM  THE  ALKALI-EARTH  METALS. 

1.  The  best  way  to  separate  THE  WHOLE  OF  THE  ALKALI- 
EARTH  METALS  from  chromium  at  the  same  time  is  to  convert 
the  latter  into  chromic  acid.  This  may  be  done  in  the  dry  or 
the  wet  way. 

a.  Dry  way.     Mix  the  powdered  substance  with  about  8  47 
times  its  weight  of  a  mixture  of  2  parts  of  sodium  carbonate 
and  1  part  of  nitre,  and  fuse  in  a  platinum  crucible.     On  treat- 
ing the  fused  mass  with  hot  water,  the  chromium  dissolves  as 
alkali  chromate  (to  be  determined  according  to  §  130),  while 
the  alkali-earth  metals  remain  in  the  residue  as  carbonates  or 
oxides  (magnesium  oxide).    If  the  residue  is  not  perfectly  white, 
extract  the  remainder  of  the  chromic  acid  from  it  by  boiling 
with  solution  of  sodium  carbonate. 

b.  Wet   way.     Suitable    for    separating    chromium    from  48 
barium,  strontium,  and  calcium. 

Nearly  neutralize  the  acid  fluid  with  sodium  carbonate,  add 
excess  of  sodium  acetate,  warm  and  pass  chlorine,  adding  sodium 
carbonate  occasionally  to  keep  the  fluid  nearly  neutral.  As 
soon  as  all  the  chromium  is  oxidized,  precipitate  with  sodium 
carbonate  by  the  aid  of  heat,  and  proceed  for  the  rest  according 
to  47  (GIBBS*).  Bromine  instead  of  chlorine  may  be  used; 

*  Zeitschr.  f.  anal.  Chem.  3,  328. 


506  SEPARATION.  [§  157. 

however,  the  oxidation  is  but  tardily  effected  by  the  mere  addi- 
tion of  bromine  water. 

2.  CHROMIUM  FROM  BARIUM,  STRONTIUM,  AND  CALCIUM.     To  49 
separate  barium  and  strontium,  precipitate  the  moderately  acid, 
hot,  dilute  solution  with  sulphuric  acid — in  the  presence  of 
strontium,  allow  to  cool  and  add  alcohol — and  when  the  pre- 
cipitate has  settled,  filter.     Chromium  cannot  be  separated  by 
ammonia  from  the  alkali-earth  metals,  since,  even  though  car- 
bonic acid  be  completely  excluded,  they  are  partially  precipi- 
tated   along   with   the    chromic   hydroxide.     From    solutions 
containing  a  salt  of  chromium,  calcium  cannot   be  precipitated 
completely  by  ammonium  oxalate ;  but  it  may  be  by  sulphuric 
acid  and  alcohol  (§  103,  1). 

3.  CHROMIUM  may  also  be  separated  from  MAGNESIUM  and  50 
small   quantities  of  CALCIUM  by  means   of  barium  carbonate. 
See  46. 

III.  SEPARATION  OF  CHROMIUM  FROM  ALUMINIUM.* 
§157. 

a.  Fuse  the  oxides  with  2  parts  of  potassium  nitrate  and  4  51 
parts  of  sodium  carbonate  in  a  platinum  crucible,  treat  the  fused 
mass  with  boiling  water,  rinse  the  contents  of  the  crucible  into 

a  porcelain  dish  or  beaker,  add  a  somewhat  large  quantity  of 
potassium  chlorate,  supersaturate  slightly  with  hydrochloric 
acid,  evaporate  to  the  consistence  of  syrup,  and  add,  during  the 
latter  process,  some  more  potassium  chlorate  in  portions,  to 
remove  the  free  hydrochloric  acid.  Dilute  now  with  water, 
and  separate  the  aluminium  and  chromium  as  directed  §  130, 
II.,  <?,  a.  If  you  omit  the  evaporation  with  hydrochloric  acid 
and  potassium  chlorate,  part  of  the  chromic  acid  will  be  reduced 
by  the  nitrous  acid  in  the  fluid,  and  chromic  hydroxide  will 
accordingly,  upon  addition  of  ammonia,  be  precipitated  with 
the  aluminium  hydroxide  (DEXTER^). 

b.  Dissolve  the  oxides  in  hydrochloric  acid,  add  soda  or  52 
potassa  solution  in  sufficient  excess  and  saturate  the  clear  green 
solution  with  chlorine  gas.     The  chromium  will  be  converted 


*  The  separation   of  aluminium  from  titanic  acid  will  be  given  under  the 
Analysis  of  Silicates, 
f  Pogg.  Anal.  89,  142. 


§  158.]  I5ASES    OF    GROUP    IV.  007 

into  chromic  acid,  and  the  v  aluminium  partially  separated. 
When  the  fluid  has  become  of  a  pure  yellow  color,  heat  to 
remove  the  excess  of  chlorine,  add  ammonium  carbonate,  and 
digest  to  destroy  the  hypochlorous  acid  and  precipitate  the  still 
dissolved  aluminium,  and  proceed  according  to  §  130,  II.,  c,  a 

(W6HLER*). 

c.  Nearly  neutralize  the  acid  solution  with  sodium  carbonate,  53 
add  sodium  acetate  in  excess,  pass  chlorine  or  add  bromine  and 
warm.  The  chromium  will  readily  be  converted  into  chromic 
acid,  especially  if  sodium  carbonate  is  added  every  now  and  then 
to  keep  the  fluid  nearly  neutral.  As  soon  as  this  is  effected 
proceed  according  to  §.  130,  II.,  c,  a  (GiBBsf). 

Fourth  Group. 

ZINC MANGANESE NICKEL COBALT FERROUS  IRON FERRIC 

IRON — (URANIUM). 

I.  SEPARATION  OF  THE  METALS  OF  THE  FOURTH  GROUP  FROM 
THE  ALKALIES. 

§158. 

A.  General  Methods. 
1.  ALL  METALS  OF  THE  FOURTH  GROUP  FROM  AMMONIUM. 

Proceed  as  for  the  separation  of  chromium  and  aluminium  54 
from  ammonium,  33.  It  must  be  borne  in  mind  that  the  oxides 
of  the  fourth  group  comport  themselves,  upon  ignition  with 
ammonium  chloride,  as  follows  :  Ferric  oxide  is  partly  converted 
into  ferric  chloride  which  volatilizes  ;  the  oxides  of  manganese 
are  converted  into  manganous  chloride  and  manganous  oxide 
with  volatilization  of  some  of  the  former  ;^  the  oxides  of 
nickel  and  cobalt  are  reduced  to  the  metallic  state,  no 
chloride  being  lost  by  volatilization  ;§  oxide  of  zinc  is  converted 
into  chloride  which  volatilizes.  It  is,  therefore,  generally 
the  safest  way  to  add  sodium  carbonate.  The  ammonium  is 
determined  in  a  separate  portion. 

*  Anal.  d.  Chem.  u.  Pkarm.  106,  131.     \  Zeitschr.  f.  anal.  Chem.  11,  424. 
f  Zeitschr.  f.  anal.  Chem.  3.  327.  §  Ib.  12,  73. 


508  SEPARATION.  [§  158. 

2.  ALL  METALS  OF   THE  FOURTH   GROUP  FROM  POTASSIUM 
AND  SODIUM. 

Mix  the  solution  in  a  flask  with  ammonium  chloride  if  55 
necessary,  add  ammonia  till  neutral  or  slightly  alkaline,  then 
yellow  ammonium  sulphide  saturated  with  hydrogen  sulphide, 
fill  the  flask  nearly  to  the  top  with  water,  cork  it,  allow  the 
precipitated  sulphides  to  subside,  and  then  filter  them  off  from 
the  fluid  containing  the  alkalies.  In  performing  this  process 
the  precautionary  rules  given  under  the  heads  of  the  several 
metals  in  question  (§§  108 — 113)  must  be  borne  in  mind.*  (If, 
notwithstanding,  the  filtrate  is  brownish,  acidify  it  with  acetic 
acid,  pass  hydrogen  sulphide,  boil  and  filter  off  the  small  quan- 
tity of  the  nickel  sulphide  which  then  separates.)  Acidify  the 
filtrate  with  hydrochloric  acid,  evaporate,  filter  off  the  sulphur 
if  necessary,  continue  the  evaporation  to  dry  ness,  ignite  the 
residue  to  remove  ammonium  salts,  and  determine  the  alkalies 
by  the  methods  given  §  152. 

B.  Special  Methods. 

1.  ZINC  FROM  POTASSIUM  AND   SODIUM,  by  precipitating  the  56 
zinc  from  the  solution  of  the  acetates  with  hydrogen  sulphide 
(see  73). 

2.  FERRIC  IRON  FROM  POTASSIUM  AND  SODIUM,  by  precipitat- 
ing with  ammonia ;  or  by  heating  the  nitrates  (see  37  and  38). 

3.  MANGANESE  FROM  THE  ALKALIES.     Mix  the  neutral   or  57 
slightly  acid  solution  with  ammonium  chloride  and  precipitate 
the  manganese  with  a  slight  excess  of  ammonium  carbonate. 
Allow  the  precipitate  to  settle  in  a  warm  place,  filter  through  a 
thick  filter,  wash  with  hot  water  and  weigh  as  protosesquioxide 
(H.  TAMMf)    In  the  filtrate  separate  the  alkalies  from  ammonium 
salts   by   gentle   ignition.     The  separation   of   manganese    as 
hydrated  peroxide  cannot  be  recommended,  as  the  precipitate 
retains  alkali.^ 

*  Manganese  may  be  separated  from  the  alkalies  according  to  §  109,  1,  c.  2,  b.- 
Nickel  and  cobalt  may  be  separated  from  the  alkalies  according  to  58,  substi- 
tuting ammonium  acetate  for  sodium  acetate. 

t  Zeitschr.  f  anal.  chem.  11,  425.  $  Ib.  11,  298. 


[§  159.  BASES    OF    GROUP    IV.  509 

II.    SEPARATION  OF  THE   METALS   OF   THE  FOURTH  GROUP    FROM 

THOSE    OF    THE    SECOND. 

§  159. 

INDEX.    (The  numbers  refer  to  those  in  the  margin.) 
Zinc  from  barium  and  strontium,  58,  59,  60,  63. 

calcium,  58,  60,  63. 
"          magnesium,  58,*60. 
Manganese  from  barium  and  strontium,  58,  59. 

'  calcium  and  magnesium,  58,  62. 

Nickel  and  cobalt  from  barium  and  strontium,  58,  59,  63. 
calcium,  58,  63. 
magnesium,  58. 

Ferric  iron  from  barium  and  strontium,  58,  59,  61. 
"  calcium  and  magnesium,  58,  61. 

A.   General  Method. 

ALL  METALS  OF  THE  FOURTH  GROUP  FROM  THE  ALKALI- 
E ART TI  METALS. 

Add  ammonium  chloride,  and,  if  acid,  also  ammonia,  and  58 
precipitate  with  ammonium  sulphide,  as  in  55.  Take  care  to 
use  slightly  yellow  ammonium  sulphide,  perfectly  saturated 
with  hydrogen  sulphide,  and  free  from  ammonium  carbonate 
and  sulphate,  and  to  employ  it  in  sufficient  excess.  Insert  the 
cork,  and  let  the  flask  stand  for  some  time  to  allow  the  precipi- 
tate to  subside,  then  wash  quickly,  and  as  far  as  practicable  out 
of  the  contact  of  air,  with  water  to  which  some  ammonium  sul- 
phide has  been  added.  Acidify  the  filtrate  with  hydrochloric 
acid,  heat,  filter  from  the  sulphur,  and  separate  the  alkali-earth 
metals,  as  directed  §  154.  If  the  filtrate  is  brownish  from  a 
little  dissolved  nickel  sulphide,  make  it  slightly  acid  with  acetic 
acid  instead  of  with  hydrochloric  acid,  add  some  alkali  acetate, 
pass  hydrogen  sulphide,  boil,  and  filter. 

If  the  quantity  of  the  alkali-earth  metals  is  rather  consider- 
able, it  is  advisable  to  treat  the  slightly  washed  precipitate  once 
more  with  hydrochloric  acid  (in  presence  of  nickel  or  cobalt,  it 
is  not  necessary  to  effect  complete  solution),  heat  the  solution 
gently  for  some  time,  and  then  reprecipitate  in  the  same  way. 

[If  we  have  merely  to  effect  removal  of  nickel  and  cobalt, 
we  may  also,  after  making  neutral  or  slightly  alkaline  with  am- 
monia, acidify  slightly  with  acetic  acid,  add  alkali  acetate,  heat, 
and  while  boiling  pass  H9S  gas  through  the  solution.  Presence 


510-  SEPARATION.  [§  159. 

of  ammonium   salts   facilitates   separation  of  the   nickel    and 
cobalt.     Compare  §  79,  e.~\ 

B.  Special  Methods. 

1.  BARIUM  AND  STRONTIUM  FROM  THE  WHOLE  OF  THE  METALS  59 
OF  THE  FOURTH  GROUP. 

Precipitate  the  barium  and  strontium  from  the  slightly  acid 
solution  with  sulphuric  acid  (§§  101, 102).  The  barium  sulphate 
should  first  be  washed  with  water  acidified  with  hydrochloric 
acid,  but  even  then  you  cannot  be  sure  of  getting  it  free  from 
iron.  The  sulphates  after  weighing  must  therefore  always  be 
tested  for  iron,  etc. 

2.  ZlNC    FROM    THE    ALKALI-EARTH    METALS.  60 

Convert  the  basic  metals  into  acetates,  and  precipitate  the 
zinc  from  the  solution  according  to  §  108,  1,  J. 

3.  FERRIC  IRON  FROM  THE  ALKALI-EARTH  METALS.  61 

a.  Mix  the  somewhat  acid  solution  with  enough  ammonium 
chloride,  boil,  add  slight  excess  of  ammonia,  boil  till  the  excess 
of  the  latter  is  nearly  expelled,  and  filter.     The  solution  is  free 
from  iron,  the  precipitate  is  free  from  calcium,  barium,  and 
strontium,  but  contains  a  very  slight  trace  of  magnesium  (H. 
ROSE*).     In  delicate  analyses,  after  moderately  washing  the 
ferric  hydroxide,  redissolve  it  in  hydrochloric  acid,  and  repeat 
the  precipitation. 

b.  Precipitate  the  iron  as  basic  ferric  acetate   or   formate, 
compare   71.     The   method  is   good,  and   can   frequently  be 
employed. 

c.  Decompose  the  nitrates  by  heat  (38).     A  good  method.! 

4.  MANGANESE  FROM  CALCIUM  AND  MAGNESIUM.  62 
[The  solution  must  not  contain  ammonium  salts.     The  man- 
ganese, calcium,  and  magnesium  may  be  present  as  chlorides, 
nitrates,  or  acetates  (or  sulphates  if  but  little  calcium  is  in  the 
solution  and  care  be  taken  to  avoid  deposition  of  calcium  sul- 
phate).    Neutralize  any  free  acid  which  may  be  present  by 
adding  sodium    carbonate  till  a  slight  precipitate  is  formed. 
Redissolve  this  precipitate  by  the  addition  of  just  sufficient  HC1. 
Add  next  sodium  acetate  to  the  solution,  then  aqueous  solution 

*  Pogg.  Annul.  100,  300. 

f  Compare  LATSCHINOW,  Zeitschr.  f.  anal  Chem.  7,  213. 


§  159.]  BASES   OF   GROUP   IV.  511 

of  bromine.  The  solution  should  at  this  point  be  rather  dilute.' 
Expose  to  a  temperature  of  50°  to  70°  a  few  hours,  till  free 
bromine  is  all  or  nearly  all  expelled  from  the  solution,  and 
filter.  Test  the  filtrate  by  adding  more  sodium  acetate  and 
more  bromine  water,  and  warming.  The  manganese  is  pre- 
cipitated as  hydrated  dioxide  which  is  liable  to  contain  soda. 
If  the  quantity  is  very  small,  it  may,  unless  great  accuracy  is 
required,  be  converted  by  ignition,  after  careful  washing  with 
hot  water,  directly  into  Mn3O4,  and  weighed.  If,  however,  the 
quantity  is  considerable,  it  should  be  dissolved  in  HC1  and 
converted  into  some  other  suitable  form  for  weighing. 

According  to  FINKENER,*  manganese  dioxide  precipitated  as 
above  described  (except  using  chlorine  instead  of  bromine)  from 
a  solution  containing  the  alkali-earth  metals,  will  not  be  entirely 
free  from  the  latter,  especially  from  barium  if  that  is  present. 
He  recommends  to  dissolve  the  manganese  precipitate  and 
reprecipitate  boiling  hot  with  ammonium  sulphide,  by  which 
means  pure  manganese  sulphide  is  obtained.  GiBusf  observes 
that  when  manganese  is  separated  from  zinc,  calcium,  and  mag- 
nesium by  the  above  process  (precipitation  as  binoxide),  a  repe- 
tition of  the  process  is  necessary  to  secure  good  results ;  but  in 
case  manganese  is  to  be  separated  only  from  calcium  and  mag- 
nesium, the  second  treatment  may  be  omitted4] 

5.  COBALT,  NICKEL,  AND  ZINC,  FROM  BARIUM,  STRONTIUM, 
AND  CALCIUM. 

Mix  with  sodium  carbonate  in  excess,  add  potassium  cyanide,  63 
heat  very  gently,  until  the  precipitated  carbonates  of  cobalt, 
nickel,  and  zinc  are  redissolved ;  then  filter  the  alkali-earth  car- 
bonates from  the  solution  of  the  cyanides  in  potassium  cyanide. 
The  former  are  dissolved  in  dilute  hydrochloric  acid,  and  sepa- 
rated according  to  §  154 ;  the  latter  are  separated  according  to 
§  160  (HAIDLEN  and  FRESENIUS§). 

*  Handbuch  d.  anal.  Chem.  v.  H.  ROSE,  6  Aufl.  v.  FiNKEfTER,  2,  925. 

f  Zeitschr.  f.  anal.  Chem.  3,  321. 

\  E.  A.  COLBY  (priv.  contrib.)  finds,  by  experiments  made  in  the  Sheffield 
Laboratory  on  the  separation  of  Ca  from  Mn,  that  by  proceeding  as  above 
directed  only  a  slight  tmweighable  trace  of  Ca  goes  down  with  the  Mn ;  while 
if  the  amount  of  free  acetic  acid  is  moderately  increased,  the  manganese  is  pre- 
cipitated entirely  free  from  calcium.  Too  much  acetic  acid,  however,  prevents 
or  delays  precipitation  of  Mn. 

§  Annal.  d.  Chem.  u.  Pharm.  43,  140. 


512  SEPARATION.  [§  160. 

« 

IH.  SEPARATION  OF  THE  METALS  OF  THE  FOURTH   GROUP 

FROM  THOSE  OF  THE  THIRD,  AND  FROM  EACH  OTHER. 
§  160. 

INDEX.     (The  numbers  refer  to  those  in  the  margin.) 
Aluminium  from  zinc,  64,  65,  71,  72,  73,  80. 

manganese,  64,  65,  66,  71,  72. 
"  nickel  and  cobalt,  64.  65,  68,  71,  72. 

ferrous  iron,  64,  65,  66,  71. 
ferric  iron,  65,  66,  76,  83.* 
Chromium  from  zinc,  manganese,  nickel,  cobalt,  and 

iron,  64,  65,  77,  78. 
"  ferric  iron,  65,  77,  78. 

Zinc  from  aluminium,  64,  65,  71,  72,  73,  80. 
"         chromium,  64,  65,  77,  78. 
"         manganese,  ,69,  73,  74,  75. 
nickel,  74,  75. 
cobalt,  74,  75,  79,  82. 
ferric  iron,  64,  70,  71,  72. 
Manganese  from  aluminium,  64,  65,  66,  71,  72. 
"  chromium,  64,  65,  77,  78. 

zinc,  69,  73,  74,  75. 
nickel,  69,  85. 
cobalt,  79,  85. 
ferric  iron,  64,  70,  71,  72. 
Nickel  from  aluminium,  64,  65,  68,  71,  72,  80. 
"  chromium,  64,  65,  93,  94. 

"  zinc,  74,  75. 

"  manganese,  69,  85. 

cobalt,  79,  81. 

ferric  iron,  64,  68,  70,  71,  72. 
Cobalt  from  aluminium,  64,  65,  68,  71,  72,  80. 
chromium,  64,  65,  77,  78. 
zinc,  74,  75,  79,  82. 
manganese,  79,  85. 
nickel,  79,  81. 

ferric  iron,  64,  68,  70,  71,  72. 
Ferrous  iron  from  aluminium,  64,  65,  66. 
"  chromium,  64,  65,  77,  7a 

ferric  iron,  64,  71,  72,  84. 
Ferric  iron  from  aluminium,  65,  66,  76,  83. 
chromium,  65,  77,  78. 
zinc,  64,  70,  71,  72. 

"  manganese,  64,  70,  71,  72. 

"  nickel,  64,  68,  70,  71,  72. 

cobalt,  64,  68,  70,  71,  72. 
ferrous  iron,  64,  71,  72,  84. 


§  160.} 


BASES   OF   GEOUP   IV. 


513 


A.  General  Methods. 

1.  Method  based  upon   the  Precipitation  of  some 
Basic  Radicals  l>y  Barium  Carbonate. 

FERRIC  IRON,  ALUMINIUM,  AND  CHROMIUM,  FROM  ALL  OTHER 
BASIC  RADICALS  OF  THE  FOURTH  GROUP. 

Mix  the  sufficiently  dilute  solution  of  the  chlorides  or  64 
nitrates,  but  not  sulphates,  which  must  contain  a  little  free  , 
acid,*  in  a  flask,  with  a  moderate  excess  of  barium  carbonate 
diffused  in  water ;  cork,  and  allow  to  stand  some  time  in  the 
cold,  with  occasional  shaking.  The  ferric  iron,  aluminium,  and 
chromium  are  completely  separated,!  whilst  the  other  basic 
radicals  remain  in  solution,  with  the  exception  perhaps  of  traces 
of  cobalt  and  nickel,  which  will  generally  fall  down  with  the 
precipitate.  This  may  be  prevented,  at  least  as  regards  nickel, 
by  addition  of  ammonium  chloride  to  the  fluid  to  be  precipi- 
tated (SCHWARZENBERG^:).  Decant,  stir  up  with  cold  water, 
allow  to  deposit,  decant  again,  filter,  and  wash  with  cold  water. 

The  precipitate  contains,  besides 
the  precipitated  metals,  barium  car- 
bonate ;  and  the  filtrate,  besides  the 
non-precipitated  metals,  a  barium 
salt. 

If  ferrous  iron  is  present,  and 
it  is  wished  to  separate  it  by  this 
method  from  ferric  iron,  etc.,  the 
air  must  be  excluded  during  the 
whole  of  the  operation.  In  that 
case,  the  solution  of  the  substance, 
the  precipitation,  and  the  washing 
by  decantation,  are  effected  in  a 
flask  (Ay  fig.  68),  through  which 
carbonic  acid  is  transmitted  (d). 

The  washing  water,  boiled  free  from  air,  and  cooled  out  of  con- 
tact of  air  (preferably  in  a  current  of  carbonic  acid),  is  poured  in 
through  a  funnel  tube  (c),  and  the  fluid  drawn  off  by  means  of 

*  If  there  is  much  free  acid,  the  greater  part  of  it  must  first  be  saturated 
with  sodium  carbonate. 

f  The  separation  of  the  chromium  requires  the  most  time, 
t  Annal.  d.  Chem.  u.  Pharm.  97,  216. 


Fig.  68. 


514  SEPARATION.  [§  160. 

a  movable  syphon  (5) ;  all  the  tubes  are  fitted  air-tight  into  the 
cork ;  they  are  smeared  with  tallow. 

2.  Method  based  upon  the  Precipitation  of  the  Metals 
of  the  Fourth  Group  by  Sodium  Sulphide  or  Ammo- 
nium Sulphide,  from  Alkaline  Solution  effected  with 
the  aid  of  Tartaric  Acid. 

ALUMINIUM   AND    CHROMIUM    FROM  THE   METALS   or  THE 
FOURTH  GROUP. 

Mix  the  solution  with  pure  normal  potassium  tartrate,*  then  65 
with  pure  solution  of  soda  or  potassa  until  the  fluid  has  cleared 
again ;  f  add  sodium  sulphide  as  long  as  a  precipitate  forms, 
allow  it  to  deposit  until  the  supernatant  fluid  no  longer  exhibits 
a  greenish  or  brownish  tint ;  decant,  stir  the  precipitate  up 
with  water  containing  sodium  sulphide,  decant  again,  transfer 
the  precipitate,  which  contains  all  the  metals  of  the  fourth 
group,  to  a  filter,  wash  with  water  containing  sodium  sulphide, 
and  separate  the  metals  as  directed  in  B.  Add  to  the  filtrate 
potassium  nitrate,  and  evaporate  to  dry  ness ;  fuse  the  residue 
in  a  platinum  dish,  and  separate  the  aluminium  from  the 
chromic  acid  formed  as  directed  §  1 57".  If  you  have  merely  to  • 
separate  aluminium  from  the  metals  of  the  fourth  group,  it  is 
better,  after  addition  of  potassium  tartrate,  to  supersaturate 
with  ammonia,  add  ammonium  chloride,  and  precipitate  in  a 
flask  with  ammonium  sulphide.  When  the  precipitate  has  set- 
tled it  is  filtered  off  and  washed  with  water  containing  ammo- 
nium sulphide.  The  filtrate  is  evaporated  in  a  platinum  dish 
with  sodium  carbonate  and  potassium  nitrate  to  dryness,  fused, 
and  the  aluminium  determined  in  the  residue. 

B.  Special  Methods. 

1.  Methods  based  upon  the  Solubility  of  Aluminium 
Hydroxide  in  Caustic  Alkalies. 

a.  ALUMINIUM  FROM  FERROUS  AND  FERRIC  IRON,  AND  SMALL 
QUANTITIES  OF  MANGANESE  (but  not  from  nickel  and  cobalt). 

Mix  the  hydrochloric  solution  with  sodium  carbonate  or  66 


*  Tartaric  acid  often  contains  aluminium,  therefore  this  is  best  made  from  the 
acid  tartrate. 

f  Chromium  and  zinc  cannot  be  obtained  together  in  alkaline  solution 
(CHANCEL,  Compt.  rend.  43,  927;  Journ.  f.  prakt.  Chem.  70,  378). 


,^  160.]  BASES    OF   GROUP   IV.  515 

pure  potash  till  the  greater  part  of  the  free  acid  is  neutralized, 
and  pour  the  solution  gradually  into  excess  of  pure  potasli 
heated  nearly  to  boiling  in  a  platinum  or  silver  dish,  stirring  all 
the  while.  Porcelain  does  not  answer  so  well,  and  glass  should 
on  no  account  be  used.  The  iron,  if  present  as  ferric  chloride, 
separates  ,as  ferric  hydroxide,  while  the  aluminium  remains  in 
solution  as  alkali  aluminate.  Hydrated  protosesquioxide  of 
iron  is  more  easy  to  wash  than  ferric  hydroxide,  hence  when 
much  iron  is  present  it  is  better  to  reduce  a  part  by  cautiously 
adding  sodium  sulphite  and  heating,  so  that  when  the  solution 
is  added  to  the  boiling  potash  a  black  granular  precipitate  may 
be  formed.  The  iron  precipitate  is  sure  to  contain  alkali,  and 
must  be  dissolved  in  hydrochloric  acid,  the  solution  boiled  witli 
nitric  acid  if  necessary,  and  reprecipitated  with  ammonia. 

To  the  alkaline  filtrate  add  a  few  drops  of  hydrochloric 
acid.  If  the  potash  was  present  in  sufficient  excess  the  precipi- 
tate will  redissolve  readily  on  stirring.  Continue  adding  hydro- 
chloric acid  till  in  excess,  boil  with  a  little  potassium  chlorate 
(to  destroy  traces  of  organic  matter),  concentrate  by  evapora- 
tion, and  throw  down  the  aluminium  according  to  §  105,  a. 
The  above  is  the  best  method  of  procedure,  but  it  is  always  to 
be  feared  that  small  quantities  of  aluminium  will  be  retained 
by  the  iron  precipitate. 

~b.  ALUMINIUM  FROM  FERROUS  AND  FEKRIC  IRON,   COBALT, 

AND  NlCKEL. 

Fuse  the  oxides  with  potassium  hydroxide  in  a  silver  era-  67 
cible,  boil  the  mass  with  water,  and  filter  the  alkaline  fluid, 
which  contains  the  aluminium,  from  the  oxides,  which  are  free 
from  aluminium,  but  contain  potassa  (H.  ROSE). 

2.  Methods  based  on  the  different  behavior  of  Am- 
monia or  Ammonium  Carbonate  in  the  presence  of  Chlo- 
ride with  solutions  of  certain  basic  radical*. 

a.  ALUMINIUM  AND  FERRIC  IRON  FROM  COBALT  AND  NICKEL. 

Ferric  iron  may  be  completely  separated  from  these  metals  68 
by  mixing  the  hot  solution  with  ammonium  chloride,  and  then 
with  excess  of  ammonia,  digesting  for  several  hours,  washing 
the  precipitate,  redissolving  in  hydrochloric  acid,  reprecipitating 
with  ammonia,  and  repeating  the  operation  a  third  time.    Nickel 


516  SEPARATION.  [§  160. 

and  cobalt  are  to  be  precipitated  from  the  filtrate  after  concen- 
tration to  a  small  volume,  as  directed  in  §  110,  1,  &,  /?. 

In  separating  iron  and  aluminium  from  nickel  and  cobalt, 
it  is  well  to  substitute  ammonium  carbonate  for  ammonia,  so  as 
to  insure  the  complete  precipitation  of  the  aluminium. 

J.  MANGANESE  FROM  NICKEL  AND  ZINC. 

The  solution  should  be  slightly  acid  and  contain  ammonium  69 
chloride.  Precipitate  the  manganese  as  white  carbonate  with 
ammonium  carbonate,  allow  to  settle  in  a  warm  place,  filter 
through  a  thick  paper,  if  necessary  double,  wash  with  hot  water, 
dry  the  precipitate  and  convert  it  into  protosesquioxide  by  igni- 
tion with  access  of  air.  This  excellent  method  was  proposed 
by  TAMM,*  and  has  given  me  good  results,  f  It  is  not  adapted 
to  the  separation  of  cobalt  from  manganese,  as  the  former  is 
partly  precipitated  with  the  latter. 

3.  Method  'based  upon   the  different  deportment  of 
neutralized  Solutions  at  boiling  heat. 

a.  FERRIC  IRON  FROM  MANGANESE,  NICKEL  AND  COBALT, 

AND  OTHER  STRONG  BASIC  METALS,  AFTER  HERSCHEL,  J  ScHWARZ- 
ENBERG,§    AND    MY    OWN    EXPERIMENTS. 

Mix  the  dilute  solution  largely  with  ammonium  chloride  (at  70 
least  40  of  NH4C1  to  1  of  MnO,NiO,  &c.),  add  ammonium 
carbonate  in  small  quantities,  at  last  drop  by  drop  and  in  very 
dilute  solution,  as  long  as  the  precipitated  iron  redissolves,  which 
takes  place  promptly  at  first,  but  more  slowly  towards  the  end. 
As  soon  as  the  fluid  has  lost  its  transparency,  without  showing, 
however,  the  least  trace  of  a  distinct  precipitate  in  it,  and  fails 
to  recover  its  clearness  after  standing  some  time  in  the  cold, 
but,  on  the  contrary,  becomes  rather  more  turbid  than  other- 
wise, the  reaction  may  be  considered  completed.  When  this 
point  has  been  attained,  heat  slowly  to  boiling,  and  keep  in 
ebullition  for  a  short  time  after  the  carbonic  acid  has  been 
entirely  expelled.  The  iron  separates  as  a  basic  ferric  salt, 
which  rapidly  settles,  if  the  solution  was  not  too  concentrated. 
Pour  off  the  hot  fluid  through  a  filter  and  wash  by  decantation 
combined  with  filtration  with  boiling  water  containing  a  little 

*  Chem.  News,  26,  37.  '  \  Annal.  de  Chim.  et  de  Phys.  49,  306. 

f  Zeitschr.  1  anal.  Chem.  11,  425.    §  Anna!,  d.  Chem.  u.  Pharm.  97,  216. 


§  160.]  BASES   OF  GKOUP   IV.  517 

• 

ammonium  chloride.  It  is  well  to  redissolve  the  precipitate  in 
hydrochloric  acid,  and  throw  down  the  iron  with  ammonia. 
The  first  filtrate  should  be  mixed  with  excess  of  ammonia.  If 
a  small  portion  of  ferric  hydroxide  is  thrown  down  here,  filter 
it  off,  dissolve  in  hydrochloric  acid,  precipitate  with  ammonia 
and  thus  free  the  small  quantity  of  iron  entirely  from  the  strong 
basic  metals  ;  if,  on  the  other  hand,  a  larger  quantity  of  iron  is 
thrown  down,  this  is  a  sign  that  the  operation  has  been  con- 
ducted improperly,  and  the  hydrochloric  solution  of  the  precipi- 
tate must  be  reprecipitated  as  above.  The  fluid  should  not 
contain  more  than  2  or  3  grm.  of  iron  in  the  litre,  and  should 
be  tolerably  free  from  sulphuric  acid,  as  when  this  is  present  it 
is  impossible  to  hit  the  exact  point  of  saturation. 

4.  Method  based  on  the  behavior  of  the  Acetates  at  a 
foiling  heat. 

FERRIC  IKON  AND  ALUMINIUM  FROM  MANGANESE,  ZINC, 
COBALT,  NICKEL,  AND  FERROUS  IRON. 

The  metals  should  be  present  in  the  form  of  chlorides.  The  71 
solution  should  be  in  a  flask.  If  much  free  acid  is  present  first 
nearly  neutralize  with  sodium  or  ammonium  carbonate  ;  the 
solution  should  remain  clear,  but  if  there  is  much  ferric  chloride 
it  should  be  of  a  deep  red  color.  Add  a  concentrated  solution 
of  neutral  sodium  or  ammonium  acetate,  not  in  large  excess,  and 
boil  for  a  short  time — long-continued  boiling  would  make  the 
precipitate  slimy.  When  the  lamp  is  removed  the  precipitate 
should  settle  rapidly,  leaving  the  supernatant  fluid  clear.  Wash 
the  precipitate  immediately  by  decantation  and  filtration  with 
boiling  water  containing  a  little  sodium  or  ammonium  acetate. 
In  very  particular  analyses  it  would  be  well  after  washing  the 
precipitate  a  little  to  redissolve  it  in  hydrochloric  acid  and 
reprecipitate. 

In  separating  ferric  from  ferrous  iron  KEICHARDT*  recom- 
mends a  slight  addition  of  ammonium  chloride  or  of  sodium 
chloride  to  prevent  oxidation  of  the  ferrous  salt. 

The  precipitate  of  basic  ferric  acetate  or  basic  aluminium 
acetate  is  best  dissolved  in  hydrochloric  acid,  in  order  to  precipi- 
tate the  basic  metals  from  this  solution  again  by  ammonia. 

*  Zeitsclir.  f .  anal.  Chem.  5,  64 


518  SEPARATION.  [§  160 

• 

This  method  is  more  suitable  to  the  separation  of  ferric  iron 
or  ferric  iron  and  aluminium  from  the  strong  basic  metals 
than  to  the  separation  of  aluminium  alone.  It  is  a  good  method, 
and  is  very  generally  used. 

[The  results  obtained  by  this  method  depend  greatly  on  the 
proper  adjustment  of  free  acetic  acid  to  the  volume  of  the  solu- 
tion which  is  boiled.  The  solution  at  this  point  may  contain 
about  four  per  cent,  (by  volume)  of  acetic  acid  sp.  gr.  l'044r 
(JEWETT*).  If  too  little  acetic  is  present,  zinc,  manganese, 
nickel,  and  cobalt  are  precipitated  in  notable  quantity  along  with 
the  iron.  If  too  much  is  present  the  precipitation  of  iron  is 
incomplete.  The  operator  may  control  the  amount  of  acid 
within  narrow  limits  by  proceeding  as  follows.  Add  the  alkali 
carbonate  to  the  cold  and  preferably  concentrated  solution  until 
a  slight  precipitate  forms  which  no  longer  redissolves  in  four 
or  five  minutes  with  occasional  shaking,  but  imparts  a  turbidity 
to  the  deep  red  solution ;  HC1  is  then  added  without  further 
delay,  slowly,  drop  by  drop,  until  the  fluid,  though  still  dark, 
becomes  clear.  Next  the  amount  of  acetic  acid  required  to 
form  four  per  cent,  of  the  final  volume  is  added,  then  sodium 
acetate  (about  ten  times  as  much  of  the  crystallized  salt  as  there 
is  iron  present,  or  more  if  but  little  iron  is  present).  Dilute 
now  to  the  final  volume,  which  should  amount  to  at  least  100 
c.c.  per  -1  grm.  iron  and  heat  to  boiling.  After  boiling  two  or 
three  minutes  only,  allow  the  iron  precipitate  to  settle.  Pour 
the  clear  liquid  through  a  filter,  then  bring  the  precipitate  upon 
the  filter  at  once  and  wash  as  above  directed.  The  iron  pre- 
cipitate contains  no  zinc  and  but  an  inappreciable  trace  of  man- 
ganese. Small  quantities  of  cobalt  and  still  more  nickel  will, 
however,  be  precipitated  with  the  iron.  When  these  two  metals 
are  present  in  considerable  quantity  a  repetition  of  the  process 
is  indispensible  when  accuracy  is  required.  Coprecipitation  of 
nickel  is  lessened  but  not  entirely  prevented  by  presence  of 
ammonium  chloride,  f 

In  carrying  out  the  process  according  to  this  plan  great  care 
must  be  taken  in  the  preliminary  neutralization  with  alkali 
carbonate  to  leave  as  little  free  mineral  acid  as  possible  without 
formation  of  a  permanent  precipitate,  otherwise  this  free  acid 

*  Am.  Cliem.  Jour.  I.  251.  f  Loc.  tit. 


£  160.]  BASES   OF   GKOUP    IV.  519 

will  liberate  enough  acetic  acid  from  the  eodium  acetate  to 
prevent  (with  that  intentionally  added)  the  precipitation  of  iron 
in  a  form  easy  to  wash. 

In  separating  large  quantities  of  iron  from  small  quantities 
of  manganese  the  addition  of  2  or  3  per  cent,  of  acetic  acid  will 
secure  a  separation  satisfactory  enough  for  most  purposes  (e.g. 
in  iron  and  iron  ores),  and  the  danger  that  the  acetic  acid  present 
may  accidentally  exceed  the  proper  limit  will  of  course  be 
lessened.] 

5.  Method  'based  on  the  different  behavior  of  the  Suc- 
cinates. 

FERRIC   IRON    (AND  ALUMINIUM)   FROM   ZINC,  MANGANESE, 

XlCKEL,    AND    COBAT. 

The  solution  should  contain  no  considerable  quantity  of  sul-  72 
phuric  acid.  If  acid,  as  is  usually  the  case,  add  ammonia  till 
the  color  is  reddish  brown,  then  sodium  or  ammonium  acetate 
(H.  HOSE)  till  the  color  is  deep  red,  finally  precipitate  with 
neutral  alkali  succinate  at  a  gentle  heat,  and  when  cool  filter  the 
ferric  succinate  from  the  solution  which  contains  the  rest  of  the 
metals.  Wash  the  precipitate  first  with  cold  water,  then  with 
warm  ammonia,  which  removes  the  greater  part  of  the  acid, 
leaving  it  darker  in  color.  Dry  and  ignite,  moisten  with  a 
little  nitric  acid,  and  ignite  again.  With  proper  care  the  sepa- 
ration is  complete,  and  especially  to  be  recommended  when  a 
relatively  large  quantity  of  iron  is  present.  The  method  may 
also  be  used  in  the  presence  of  aluminium.  The  latter  falls 
down  completely  with  the  iron  (E.  MITSCHERLICH,  PAGELS*). 

6.  Methods  based  upon  the  different  deportment  of  the 
several  Sulphides  with  Acids,  or  of  Add  Solutions  with 
Hydrogen  Sulphide. 

a.  Zixc  FROM  ALUMINIUM  AND  MANGANESE. 

The  solution  of  the  acetates,  which  must  be  free  from  in-  73 
organic  acids,  and  must  contain  a  sufficient  excess  of  acetic  acid, 
is  precipitated  with  hydrogen  sulphide,  which  throws  down  the 
zinc  only  (§  108,  b).      The   metals  are  usually  most    readily 
obtained   in  the  form  of  acetates,  by  converting   them   into 

*  Jahresber.  v.  KOPP  u.  WILL.  1858,  617. 


520  SEPARATION.  [§  160. 

sulphates,  and  adding  a  sufficient  quantity  of  barium  acetate. 
Hydrogen  sulphide  is  then  conducted,  without  application  of 
heat,  into  the  unfiltered  fluid,  to  which,  if  necessary,  some  more 
acetic  acid  has  been  added.  The  precipitate,  which  consists  of 
a  mixture  of  zinc  sulphide  and  barium  sulphate,  is  washed 
with  water  containing  hydrogen  sulphide.  It  is  then  heated 
with  dilute  hydrochloric  acid,  the  solution  filtered,  and  the  zinc 
in  the  filtrate  determined  as  directed  §  108,  a.  The  other 
metals  a-re  determined  in  the  fluid  filtered  from  the  zinc  sul- 
phide, after  removal  of  the  barium  by  precipitation.  BftuNNERf 
has  proposed  a  modification  of  this  process,  especially  for  the 
separation  of  zinc  from  nickel. 

b.  ZINC  FKOM  NICKEL,  COBALT,  AND  MANGANESE. 

To  the  hydrochloric  solution  add  sodium  carbonate  till  a  74 
permanent  precipitate  just  forms,  and  then  a  drop  or  two  of 
hydrochloric  acid  to  redissolve  the  precipitate.  Now  pass 
hydrogen  sulphide  till  the  precipitate  of  zinc  sulphide  ceases  to 
increase.  Add  a  few  drops  of  a  very  dilute  solution  of 
sodium  acetate,  and  continue  passing  the  gas  for  some  time. 
When  all  the  zinc  is  precipitated,  allow  to  stand  for  twelve 
hours,  filter,  wash  with  hydrogen  sulphide  water,  and  determine 
the  nickel  and  cobalt  in  the  filtrate  (SMITH  and  BRUNNER*)  A 
good  method  ;  compare  KLAYE  and  DEus.f  The  method  is 
also  adapted  for  separating  zinc  from  manganese. 

[Precautions. — Bear  in  mind  that  Zn  can  be  precipitated 
from  solutions  containing  free  HC1,  but  only  in  case  the 
amount  of  the  latter  is  very  small.:):  When  ZnS  is  precipi- 
tated the  amount  of  HC1  set  free  may  be  sufficient  to  prevent 
complete  precipitation  of  the  Zn.  Addition  of  sodium  acetate 
converts  this  HC1  into  NaCl,  and  allows  the  formation  of  ZnS 
to  continue.  Care  must  be  taken  not  to  add  enough  sodium 
acetate  to  convert  all  the  HC1  into  NaCl,  for  in  that  case  NiS 
and  CoS  will  be  precipitated.] 

c.  ZINC  FROM  NICKEL  COBALT,  AND  MANGANESE. 

[Zinc  can  be  precipitated  by  hydrogen  sulphide  from  a  cold  75 
solution  containing  a  sufficient  amount  of  free  acetic  acid  to 

*  Dingler's  polyt.  Journ.  150,  369;  Chem.  Centralbl.  1859,  26. 
.     f  Zeitschr.  f.  anal.  Chem.  10,  200. 

\  STOKER  and  ELIOT,  Mem.  Am.  Acad.  Arts  and  Sciences,  viii.  95. 


§  160.]  BASES   OF   GEOUP  IV.  521 

prevent  precipitation  of  nickel  and  cobalt.  To  effect  separation 
by  this  means*  add  sodium  or  potassium  carbonate  to  the  solu- 
tion till  it  is  slightly  alkaline.  If  a  large  quantity  of  any  free 
volatile  acid  is  present  it  may  be  previously  removed  by 
evaporation.  Dissolve  the .  precipitate  produced  by  the  alkali 
carbonate  (without  filtering)  in  acetic  acid,  and  add  a  large 
quantity  more  of  acetic  acid.  Precipitate  the  zinc  by  passing 
H2S  through  the  cold  moderately  diluted  solution.  Wash  the 
sulphide  of  zinc  with  water  to  which  hydrogen  sulphide  and  a 
little  ammonium  acetate  has  been  added.  The  zinc  sulphide 
should  not  be  dark-colored.  This  will  only  be  the  case  when 
not  enough  acetic  is  present  to  prevent  precipitation  of  nickel 
or  cobalt.  Cobalt  and  nickel  may  be  best  separated  from  the 
filtrate  by  evaporating  till  the  greater  part  of  the  acetic  acid  is 
removed,  then  adding  some  ammonium  chloride  and  ammonia 
to  slight  alkaline  reaction,  evaporating  further  till  the  reaction 
becomes  acid,  heating  finally  to  boiling,  and  passing  hydrogen 
sulphide  through  the  solution,  as  directed  in  §  110,  1,  b,  ft. — A 
good  method.] 

7.  Different  deportment  of  the  several  Oxides  with 
Hydrogen  Gas  at  a  red  heat. 

FERRIC  IRON  FROM  ALUMINIUM  AND  CHROMIUM. 

[Precipitate  with  ammonia,  heat,  filter,  ignite,  and  weigh.  76 
Triturate,   and  weigh   off   a  portion  in  a  porcelain  crucible. 
Ignite  to  redness  in  a  stream  of  hydrogen  gas  as  long  as  water 
forms  (about  one  hour).     Then  ignite  over  the  blast-lamp  in  a 
current  of  mixed  hydrogen  and  hydrochloric  acid  gases. 

This  leaves  aluminium  and  chromium  oxides  in  a  state  of 
purity ;  the  iron  volatilizes  as  ferrous  chloride,  and  is  determined 
by  the  loss.  (Method  of  RIVOT  and  DEVILLE  modified.)  This 
method  is  further  modified  by  COOKED  who  by  means  of  a 
platinum  boat  in  a  platinum  tube  ignites  the  mixed  oxides  over 
a  Bunsen  lamp  half  an  hour  in  a  current  of  hydrogen,  then 
alternately  in  HC1  gas  and  hydrogen  till  the  light  color  shows 
that  iron  has  been  removed.] 

*  ROSE  and  FINKENER,  Anal.  Chem.  ii.  129  and  143. 
f  Zeitschr.  f.  anal.  Chem.  6,  226. 


SEPARATION  [g  160. 

8.  Methods  based  upon  the  different  capacity  of  the 
several  Oxide®  to  be  converted  ~by  Oxidizing  Agents  into 
higher  Oxides,  or  ly  Chlorine  into  higher  Chlorides. 

a.  CHROMIUM  FROM  ALL  THE  METALS  OF  THE  FOURTH  GROUP, 
AND  FROM  ALUMINIUM. 

Fuse  the  oxides  with  potassium  nitrate  and  sodium  carbon-  77 
ate  (coinp.  51),  boil  the  mass  with  water,  add  a  small  quantity 
of  alcohol,  and  heat  gently  for  several  hours.  Filter  and  deter- 
mine in  the  filtrate  the  chromium  as  directed  §  130,  and  in  the 
residue  the  metals  of  the  fourth  group.  The  following  is  the 
theory  of  this  process :  the  oxides  of  zinc,  cobalt,  nickel,  iron, 
and  partly  that  of  manganese,  separate  upon  the  fusion,  whilst, 
on  the  other  hand,  potassium  manganate  (perhaps  also  some 
ferrate)  and  chromate  are  formed.  Upon  boiling  with  water, 
part  of  the  manganic  acid  of  the  potassium  manganate  is  con- 
verted into  permanganic  acid  at  the  expense  of  the  oxygen  of 
another  part,  which  is  reduced  to  the  state  of  binoxide ;  the 
latter  separates,  whilst  the  potassium  salts  are  dissolved.  The 
addition  of  alcohol,  with  the  application  of  a  gentle  heat,  effects 
the  decomposition  of  the  potassium  manganate  and  permanga- 
nate, manganese  binoxide  being  separated.  Upon  filtering  the 
mixture,  we  have  therefore  now  the  whole  of  the  chromium  in 
the  filtrate  as  alkali  chromate,  and  all  the  oxides  of  the  fourth 
group  on  the  filter.  Aluminium,  if  present,  will  be  found  partly 
in  the  residue,  partly  as  alkali  aluminate  in  the  filtrate  ;  proceed 
with  the  latter  according  to  51. 

If  you  have  to  deal  with  the  native  compound  of  sesqui- 
oxide  of  chromium  with  protoxide  of  iron  (chromic  iron)  the 
above  method  does  not  answer.  This  substance  may  be  decom- 
posed by  fusion  with  cryolite  and  potassium  disulphate.* 

b.  The  radicals  to  be  separated  may  be  in  the  form  of  a  78 
solution  of  their  salts ;  nearly  neutralize  the  solution,  add 
sodium  acetate,  heat  and  convert  the  chromium  into  chromic 
acid  by  passing  chlorine,  compare  53.  If  ferric  iron  and 
aluminium  are  present,  they  will  separate  during  boiling  by  the 
action  of  the  sodium  acetate,  while  the  chromic  acid  and  any 
zinc  will  remain  in  solution.  If  manganese,  nickel,  and  cobalt 
are  present,  the  method  loses  its  simplicity ;  the  manganese  is 
precipitated  as  hydrated  peroxide  with  a  portion  of  the  cobalt, 

*  GIBBS  and  CLARK,  Am.  Jour.  Sci.  II  ser.  48,  198. 


§  160.]  BASES    OF    GKOUP    IV.  523 

almost  the  whole  of  the  nickel  and  some  zinc,  while  the  chromic 
acid  remains  in  solution  with  the  principal  amount  of  the  zinc 
and  the  rest  of  the  cobalt  and  nickel  (W.  GIBBS). 

9.  Method  based  upon  the  different  deportment  of  the 
Nitrites. 

COBALT  FROM  NICKEL,  ALSO  FROM  MANGANESE  AND  ZINC. 

The  separation  of  cobalt  as  tripotassium  cobaltic  nitrite  was  79 
recommended  first  by  FISCHER,*  afterwards  by  A.  STROMEYER.+ 
GEXTH  and  GIBBS,^:  H.  ROSE,§  FR.  GAUHE,[  and  myself  (com- 
pare last  edition  of  this  work).  The  results  are  quite  satisfac- 
tory both  in  presence  of  much  cobalt  and  little  nickel,  and  in 
the  presence  of  little  cobalt  and  much  nickel ;  but  the  process 
is  peculiarly  good  for  the  latter  case.  However,  it  is  absolutely 
necessary  that  barium,  strontium,  and  calcium  should  be  absent, 
as  in  their  presence  nickel  is  thrown  down  as  triple  nitrite  of 
nickel,  potassium,  and  alkali-earth  metal  (KUNZEL,  O.  L.  ERD- 
MANN^T).  The  best  way  of  proceeding  is  as  follows :  The 
solution  (from  which  any  iron  must  first  be  separated)  is  evapo- 
rated to  a  small  bulk,  and  then,  if  much  free  acid  is  present, 
neutralized  with  potassa.  Then  add  a  concentrated  solution  of 
potassium  nitrite  (previously  neutralized  with  acetic  acid  and 
filtered  from  any  flocks  of  silica  and  alumina  that  may  have 
separated)  in  sufficient  quantity,  and  finally  acetic  acid,  till  any 
flocculent  precipitate  that  may  have  formed  from  excess  of 
potassa  has  redissolved  and  the  fluid  is  decidedly  acid.  Allow 
it  to  stand  at  least  for  twenty-four  hours  in  a  warm  place,  take 
out  a  portion  of  the  supernatant  fluid  with  a  pipette,  mix  it  with 
more  potassium  nitrite,  and  observe  whether  a  further  precipita- 
tion takes  place  in  this  after  long  standing.  If  no  precipitate  is 
formed  the  whole  of  the  cobalt  has  fallen  clown,  otherwise  the 
small  portion  must  be  returned  to  the  principal  solution,  some 
more  potassium  nitrite  added,  and  after  long  standing  the  same 
test  applied.  Thus,  and  thus  alone,  can  the  analyst  be  sure  of 
the  complete  precipitation  of  the  cobalt.  Finally  filter  and 
treat  the  precipitate  according  to  §  111,  1,  d.  Boil  the  filtrate 

*  Pogg.  Anna}.  72,  477.  }  Ib.  104,  309. 

f  Annal.  d.  Chem.  u.  Phann.  96,  218.          §  Pogg.  Annal.  110,  412. 

|  Zeitschr.  f .  anal.  Chem.  5,  74. 

•y  Zeitschr.  f .  anal.  Chem.  3,  161 ;  Journ.  f .  prakt.  Chem.  97,  387. 


524  SEPAKATION.  [§  160. 

with  excess  of  hydrochloric  acid,  precipitate  with  potash,  redis- 
solve  the  precipitate  in  hydrochloric  acid,  throw  down  the 
nickel  according  to  §  110,  1,  £,  a  or  /?,  as  sulphide,  and  then 
convert  into  metal.  In  this  manner  alone  can  the  nickel  be 
obtained  pure,  as  the  original  nitrate  contains  so  much  alkali 
salt  and  also  generally  alumina  and  silica. 

[When  nickel  and  cobalt  are  obtained  in  the  form  of 
sulphides  in  the  process  of  separation  from  other  metals,  the 
mixed  sulphides  may  be  converted  into  metals  without  previous 
separation,  by  the  same  process  that  is  described  for  nickel 
sulphide  §  110,  1,  5,  and  2.  Cobalt  may  then  be  separated 
from  a  nitric  acid  solution  of  the  two  metals  and  nickel  estimated 
by  difference.] 

10.  Methods  based  upon  the  different  deportment  with 
Potassium  Cyanide. 

a.  ALUMINIUM  FROM  ZINC,  COBALT,  AND  NICKEL. 

Mix  the  solution  with  sodium  carbonate,  add  potassium  80 
cyanide  in  sufficient  quantity,  and  digest  in  the  cold,  until  the 
precipitated  zinc,  cobalt,  and  nickel  carbonates  are  redissolved. 
Filter  off  the  undissolved  aluminium  precipitate,  wash,  and 
remove  the  alkali  which  it  contains,  by  resolution  in  hydro- 
chloric acid  and  reprecipitation  by  ammonia  (FRESENIUS  and 
HAIDLEN  *). 

b.  COBALT  FROM  NICKEL. 

LIEBIG'S  method, f  which  depends  upon  the  conversion  of  81 
the  cobalt  into  potassium  cobalticyanide,  and  of  the  nickel  into 
double  nickel  and  potassium  cyanide,  has  been  carefully  studied 
in  my  laboratory  by  FR.  GAUHE.^:  It  has  been  thus  found  that 
boiling  the  solution  containing  potassium  cyanide  and  hydro- 
cyanic acid  (LIEBIG'S  first  method)  does  not  completely  convert 
the  double  cobalt  and  potassium  cyanide  first  formed  into  . 
potassium  cobalticyanide,  but  that  passing  chlorine  (LIEBIG'S 
second  method)  effects  a  ready  and  thorough  conversion.  The 
method  then  gives  a  very  excellent  separation,  and  is  more  par- 
ticularly to  be  recommended  where  the  quantity  of  nickel  is 
small  in  proportion  to  the  cobalt.  We  proceed  as  follows, 

*  Annal.  d.  Chem.  u.  Pharm.  43,  129.  f  lb.,  65,  244,  and  87,  128. 

\  Zeitschr.  f.  anal.  Chem.  5,  75. 


§  160.]  BASES   OF   GROUP   IV.  525 

taking  a  hydrochloric  solution  of  the  metals :  Remove  the 
greater  part  of  the  free  acid  by  evaporation  or  neutralize  it  by 
potash,  add  pure  potassium  cyanide  till  the  precipitate  first 
formed  has  redissolved ;  then  add  more  cyanide,  dilute,  boil  for 
sorhe  time  or  not,  as  you  like,  pass  chlorine  through  the  cold 
fluid,  adding  potash  or  soda  occasionally,  so  that  the  fluid  may 
remain  strongly  alkaline  to  the  end.  Bromine  may  be  used 
instead  of  chlorine,  and  indeed  is  far  more  convenient.  In  the 
course  of  an  hour  the  whole  of  the  nickel  will  have  precipi- 
tated as  black  hydrate  of  the  sesquioxide.  Having  taken  out  a 
portion  and  satisfied  yourself  of  this  by  addition  of  a  further 
quantity  of  chlorine  or  bromine,  filter,  and  wash  with  boiling 
water.  The  precipitate  always  retains  alkali,  and  must  be  redis- 
solved in  hydrochloric  acid,  and  estimated  according  to  §  110, 
1,  a,  or  2. 

As  regards  the  cobalt,  it  is  most  convenient  to  estimate  it 
by  difference.  But  if  you  wish  to  make  a  direct  estimation,  it 
will  be  advisable,  in  consequence  of  the  large  quantity  of  salts 
present  in  solution,  first  to  evaporate  to  dryness  with  excess  of 
hydrochloric  acid,  to  take  up  the  residue  with  a  little  water, 
and  to  heat  in  a  large  platinum  dish,  with  the  addition  of 
excess  of  pure  concentrated  sulphuric  acid  till  the  greater  part 
of  the  sulphuric  acid  has  escaped.  The  red  mass,  consisting 
principally  of  alkali  disulphate,  is  then  treated  with  water,  and 
the  cobalt  estimated  according  to  §  111,  1,  c. 

c.  COBALT  FROM  ZINC. 

Add  to  the  solution  of  the  two  metals,  which  must  contain  82 
Borne  free  hydrochloric  acid,  common  potassium  cyanide  (pre- 
pared by  LIEBIG'S  method),  in  sufficient  quantity  to  redissolve 
the  precipitate  of  cobalt  cyanide  and  zinc  cyanide  which  forms 
at  first ;  then  add  a  little  more  potassium  cyanide,  and  boil  some  • 
time,  adding  occasionally  one  or  two  drops  of  hydrochloric  acid, 
but  not  in  sufficient  quantity  to  make  the  solution  acid.  After 
cooling  add  some  chlorine  or  bromine,  and  digest  for  some 
time  to  complete  the  conversion  of  the  cobalt  into  potassium 
cobalticyanide.  Mix  the  solution  with  hydrochloric  acid  in  an 
obliquely  placed  flask,  and  boil  until  the  zinc  cobalticyanide 
which  precipitates  at  first  is  redissolved,  and  the  hydrocyanic 
acid  completely  expelled.  Add  solution  of  soda  or  potassa  in 


526  SEPARATION.  [§  160. 

excess,  and  boil  until  the  fluid  is  clear ;  the  solution  may  now 
be  assumed  to  contain  all  the  cobalt  as  potassium  cobalticyanide, 
and  all  the  zinc  as  a  compound  of  oxide  of  zinc  and  alkali. 
Precipitate  the  zinc  by  hydrogen  sulphide  (§  108).  Filter,  and 
determine  the  cobalt  in  the  filtrate  as  in  81.  The  process  is  ' 
simple  and  the  separation  complete  (FRESENIUS  and  HAIDLEN). 

11.  Methods  based  upon  the  Volumetric  Determina- 
tion of  one  of  the  Metals ,  and  the  finding  of  the  other 
from  the  difference. 

a.  FERRIC  IRON  FROM  ALUMINIUM, 

Precipitate  both  metals  with  ammonia  (§  105,  a,  and  §  113,  83 
1).  Dissolve  the  weighed  residue,  or  an  aliquot  part  of  it,  by 
digestion  with  concentrated  hydrochloric  acid,  or  by  fusion  with 
bisulphate  of  potassa  and  treatment  with  water  containing  sul- 
phuric acid,  and  determine  the  iron  volumetrically  as  directed 
§  113,  3,  a  or  ~b.  The  alumina  is  found  from  the  difference. 
This  is  an  excellent  method,  and  to  be  recommended  more  par- 
ticularly in  cases  where  the  relative  amount  of  iron  is  small. 
If  you  have  enough  substance,  it  is  of  course  much  more  con- 
venient to  divide  the  solution,  by  weighing  or  measuring,  into 
2  portions,  and  determine  in  the  one  the  sesquioxide  of  iron  -j- 
alumina,  in  the  other  the  iron. 

1).  FERRIC  IRON  FROM  FERROUS  IRON  (ZiNC  AND  NICKEL). 

oc.  Determine  in  a  portion  of  the  substance  the  total  amount  84 
of  the  iron  as  sesquioxide,  or  by  the  volumetric  way.  Dissolve 
another  portion  by  warming  with  sulphuric  acid  in  a  flask 
through  which  carbonic  acid  is  conducted,  to  exclude  the  air ; 
dilute  'the  solution,  and  determine  the  protoxide  of  iron  volu- 
metrically (§  112,  2,  a).  The  difference  gives  the  quantity  of 
the  sesquioxide.  Or,  dissolve  the  compound  in  like  manner 
in  hydrochloric  acid,  and  determine  the  ferric  chloride  with 
sodium  thiosulphate  according  to  §  113,  3,  ~b.  In  this  case  the 
difference  gives  the  ferrous  iron.  If  it  is  desired  to  determine 
the  ferrous  chloride  in  the  hydrochloric  solution  directly,  it  will 
be  well  to  use  PENNY'S  method  (§  112,  2,  &).  If  the  compound 
in  which  the  ferrous  and  ferric  basic  radicals  are  to  be  estimated 
is  decomposed  by  acids  with  difficulty,  heat  it  with  a  mixture 
of  4  parts  sulphuric  acid  and  1  part  water  (or  with  hydrochloric 


§  160.]  BASES   OF   GROUP  IV.  527 

acid)  in  a  sealed  tube  for  2  hours  at  210°  (MrrscHERLicHf). 
Or,  if  this  is  not  enough,  fuse  it  with  borax  (1  part  mineral,  5 
to  6  vitrified  borax)  in  a  small  retort,  connected  with  a  flask 
containing  nitrogen  (produced  by  combustion  of  phosphorus  in 
air)  ;  an  atmosphere  of  carbonic  acid  is  less  suitable.  Triturate 
the  fused  mass  with  the  glass,  and  dissolve  in  boiling  hydro- 
chloric acid  in  an  atmosphere  of  carbonic  acid  (HERMANN  v. 
KOBELL).  Or,  as  will  generally  be  the  best  way,  you  may  dis- 
solve the  substance  in  a  mixture  of  hydrofluoric  and  hydro- 
chloric or  hydrofluoric  and  sulphuric  acids  with  exclusion  of 


FIG.  69. 


air.  COOKE  *  dissolves  silicates  in  a  mixture  of  sulphuric  and 
hydrofluoric  acids  in  an  atmosphere  of  steam  and  carbonic  acid, 
and  determines  the  ferrous  iron  by  means  of  potassium  per- 
manganate. 

Fig.  69  exhibits  his  apparatus.  To  the  sides  of  a  copper 
water-bath  are  attached  three  tubes.  The  tube  on  the  left  con- 
nects with  a  Mariotte's  flask  to  maintain  the  water  at  a  constant 
level.  The  upper  tube  on  the  right  connects  with  a  carbonic 
acid  gas  generator,  while  the  third  tube  carries  off  any  overflow 
of  water  to  the  sink. 

On  the  cover  of  the  water-bath  close  to  the  rim  is  a  circular 
groove,  which  receives  the  edge  of  an  inverted  glass  funnel. 
When  the  apparatus  is  in  use  this  groove  is  kept  full  of  water 
by  the  spray  from  the  boiling  liquid,  and  thus  forms  a  perfect 


*  Am.  Jour.  Science,  3d  ser.,  44,  347. 
- Jour.  f.  prnkt,  Chem.,  81.  108  and  83.  455 


528  SEPAEATION.  [§  160. 

water-joint ;  but  in  order  to  secure  this  result  the  bath  must  be 
kept  nearly  full  of  water,  and  holes  for  the  ready  escape  of  the 
steam  and  spray  should  be  provided  in  the  rings,  which  cover 
the  bath  and  adapt  it  for  vessels  of  various  sizes.  By  this 
arrangement  the  funnel  may  be  kept  filled  with  an  atmosphere 
of  steam  or  of  carbonic  acid  for  an  indefinite  period.  More- 
over, we  can  either  pour  in  fresh  quantities  of  solvent,  or  we 
can  stir  up  the  material,  in  the  vessel  within,  introducing  a 
tube-funnel  or  stirrer  through  the  spout  of  the  covering  funnel. 
The  finely  pulverized  substance  (-J  to  1  grm.)  is  placed  in  a 
large  platinum  crucible.  Upon  it  pour  a  mixture  of  dilute 
sulphuric  acid  (sp.  gr.  1*5)  with  as  little  hydrofluoric  acid  as 
experience  may  show  is  required  to  dissolve  or  decompose  the 
substance,  stirring  up  the  material  with  a  platinum  spatula. 
The  crucible  is  next  transferred  to  the  water-bath,  the  covering 
funnel  put  in  place,  water  poured  into  the  groove,  the  interior 
filled  with  carbonic  acid,  and  the  lamp  lighted.  As  soon  as  the 
water  boils,  the  supply  of  carbonic  acid  is  stopped  ;  and  if  the 
water-level  has  been  properly  adjusted,  the  apparatus  will  take 
care  of  itself,  the  groove  will  be  kept  full  of  water,  arid  the 
interior  of  the  funnel  full  of  steam.  If  the  materials  cake  on  the 
bottom  of  the  crucible,  as  is  not  unfrequently  the  case  when  a 
large  amount  of  insoluble  sulphate  is  formed,  the  lamp  may  be 
removed,  the  apparatus  again  filled  with  carbonic  acid,  and  the 
contents  of  the  crucible  stirred  up  by  aid  of  a  stout  platinum 
wire  about  two  inches  long,  fused  to  the  end  of  a  glass  tube. 
Anything  adhering  to  the  rod  can  easily  be  washed  back  into 
the  crucible  by  directing  the  jet  from  the  wash-bottle  down  the 
throat  of  the  covering  funnel.  The  lamp  may  then  be  replaced, 
the  current  of  carbonic  acid  interrupted,  and  the  process  of 
digestion  continued .  When  the  decomposition  is  complete,  the 
current  of  carbonic  acid  gas  is  re-established,  the  lamp  extin- 
guished, and  the  air-tube  of  the  Mariotte's  flask  raised  until  its 
lower  end  is  above  the  level  of  the  overflow.  A  slow  current 
of  water  is  thus  caused  to  flow  through  the  bath,  which  soon 
cools  down  the  whole  apparatus.  The  crucible  may  now  be 
removed,  its  contents  washed  into  a  beaker-glass,  and  the  solu- 
tion diluted  with  pure  water  until  the  volume  is  about  500  c.c., 
when  the  amount  of  ferrous  iron  present  can  be  determined 
with  a  solution  of  potassium  permanganate  in  the  usual  way. 


§  161.]  BASES   OF   GROUP   IV.  529 

Many  iron  compounds  in  fine  powder  are  completely  decom- 
posed by  boiling  a  few  minutes  only  with  the  mixed  acids 
above  mentioned.  If  a  preliminary  experiment  shows  this  to 
be  the  case,  a  simple  and  satisfactory  way  of  effecting  a  solu- 
tion is  to  boil  the  substance  with  the  solvent  acids  in  a  platinum 
crucible  of  40  to  50  c.c.  capacity,  provided  with  a  well-fitting 
concave  cover.  By  watching  the  escaping  vapor,  one  <jan  regu- 
late the  boiling  so  as  to  prevent  access  of  air  without  appreciable 
mechanical  loss.  If  on  removing  the  cover  the  decomposition 
is  complete,  the  operation  may  be  considered  successful.  Put 
the  crucible  and  its  contents  at  once  into  cold  water  in  a  beaker 
and  titrate  with  permanganate  (or  thiosulphate  if  HC1  has  been 
used). 

Iron  may  also  be  determined  volumetrically  in  presence  of 
zinc,  nickel,  etc.  It  is,  indeed,  often  the  better  way,  instead 
of  effecting  the  actual  separation  of  the  oxides,  to  determine  in 
one  portion  of  the  solution  the  iron  -|-  zinc  or  -(-  nickel,  in 
another  portion  the  iron  alone,  and  to  find  the  quantity  of  the 
other  metal  by  the  difference.  However,  this  can  be  done  only 
in  cases  where  the  quantity  of  iron  is  relatively  small. 

12.  Cobalt  and  Nickel  from  Manganese. 

To  the  acid  solution  add  sodium  carbonate  in  excess,  then  85 
acetic  acid  in  liberal  excess,  then  to  the  clear  fluid,  containing 
say  a  grm.  of  nickel  or  cobalt,  30  to  40  c.c.  of  sodium  acetate 
solution  (1  in  10),  and  pass  hydrogen  sulphide  to  saturation, 
keeping  at  70°.  Filter  off  the  precipitated  nickel  or  cobalt  sul- 
phide, wash  and  dry  it.  Concentrate  the  filtrate  by  evapora- 
tion, add  ammonium  sulphide,  and  then  acetic  acid,  thus 
obtaining  a  second  precipitate  of  nickel  or  cobalt  sulphide. 
Test  the  filtrate  again  in  the  same  manner.  In  the  united  pre- 
cipitates determine  the  nickel  or  cobalt  according  to  §  110$  1,  5, 
or  §  111,  1,  c;  m  the  filtrate,  the  manganese  according  to 
§  109,  2, 

IY.  SEPARATION  OF  IKON,  ALUMINIUM,  MANGANESE,  CALCIUM, 
MAGNESIUM,  POTASSIUM  AND  SODIUM. 

§161. 

As  these  metals  are  found  together  in  the  analysis  of  most 
silicates,  and  also  in  many  other  cases.  I  devote  a  distinct  para- 


530  SEPARATION.  [§  161. 

graph  to  the  description  of  the  methods  which  are  employed  to 
effect  their  separation. 

1.  Method  based  upon  the  employment  of  Barium   Car- 
bonate (particularly  applicable  in  cases  where  the  mixture  con- 
tains only  a  small  proportion  of  calcium). 

The  solution  should  contain  no  free  chlorine,  and  the  iron  86 
should  be  all  in  the  form  of  ferric  salt.  Precipitate  the  iron 
and  aluminium  by  barium  carbonate  *  (46  and  64),  dissolve  the 
precipitate  in  hydrochloric  acid,  throw  down  the  barium  with 
sulphuric  acid,  filter,  and  estimate  the  iron  and  aluminium 
according  to  one  of  the  methods  given  §  160,  by  preference  83, 
at  least  when  the  quantity  of  aluminium  is  not  too  small. 

To  the  filtrate  from  the  barium  carbonate  precipitate  add 
hydrochloric  acid,  heat,  throw  down  the  barium  with  sulphuric 
acid,  added  just  in  excess.  Filter  off  the  precipitate,  wash  till 
f ree  from  soluble  sulphate,  concentrate  if  necessary,  precipitate, 
and  determine  the  manganese  as  sulphide  (§  109,  2).  To  the 
filtrate  add  hydrochloric  acid,  heat,  filter  off  the  sulphur,  pre- 
cipitate the  lime  with  oxalate  of  ammonia,  and  finally  separate 
the  magnesia  from  the  alkalies  by  one  of  the  methods  given  § 
153. 

2.  Method  based  upon  the  application  of  Alkali  Acetates 
or  Formates. 

Remove  by  evaporation  any  very  considerable  excess  of  acid  87 
which  may  be  present,  dilute,  add  sodium  carbonate,  f  until  the 
fluid  is  nearly  neutral,  then  sodium  acetate  (or  sodium  formate) 
and  precipitate  iron  and  aluminium,  observing  all  directions 
given  in  71.  Wash  the  precipitate  well,  dissolve  in  hydrochloric 
acid,  precipitate  the  solution  with  ammonia  (37),  dry,  ignite, 
and  weigh.  Dissolve  in  concentrated  hydrochloric  acid,  or 
digest  it  with  1 6  times  its  weight  of  a  mixture  of  8  parts  sul- 
phuric acid  and  3  parts  water,  or  fuse  it  for  a  long  time  with 

*  Before  adding  the  barium  carbonate,  it  is  absolutely  indispensable  to  ascer- 
tain whether  a  solution  of  it  in  hydrochloric  acid  is  completely  precipitated  by 
sulphuric  acid,  so  that  the  nitrate  leaves  no  residue  upon  evaporation  in  a  pla- 
tinum dish. 

f  In  cases  where  it  is  intended  to  estimate  the  alkalies  in  the  filtrate,  ammo- 
nium salts  must  be  used  instead  of  the  sodium  salts.  If,  however,  it  is  intended 
to  precipitate  manganese  subsequently  with  bromine,  ammonium  salts  must  not 
be  introduced  into  the  solution. 


§  161.]  BASES    OF    GROUP   IV.  531 

bisulpliate  of  potassa,  dissolve  in  water,  and  determine  the  iron 
volumetrically  as  in  §  113,  3,  a  or  &.  The  difference  gives  the 
quantity  of  the  aluminium.  If  any  silicic  acid  remains  behind 
on  dissolving  the  precipitate,  it  is  to  be  collected  on  a  filter, 
ignited,  weighed,  and  deducted  from  the  alumina.  The  filtrate 
contains  the  manganese,  the  alkali-earth  metals,  and  the  alkalies. 
Precipitate  the  manganese  with  ammonium  sulphide  (§  109,  2), 
boil  with  hydrochloric  acid  and  filter  off  the  sulphur,  precipi- 
tate the  calcium,  after  addition  of  ammonia,  with  ammonium 
oxalate,  and  lastly,  after  removing  the  ammonium  salts  by  igni- 
tion, precipitate  the  magnesium  from  the  hydrochloric  acid 
solution  of  the  residue  with  ammonium  sodium  phosphate. 
However,  if  it  is  intended  to  estimate  the  alkalies,  the  magne- 
sium must  be  separated  by  one  of  the  processes  in  §  153,  4.  This 
method  is  convenient,  and  gives  good  results,  especially  in  the 
presence  of  much  iron  and  little  aluminium.  Since  aluminium 
is  not  precipitated  by  alkali  acetates  or  formates  with  the  same 
certainty  as  iron,  it  is  necessary  to  test  the  weighed  manganese 
sulphide  for  aluminium. 

[This  method  is  to  be  recommended  when  manganese  is  pres- 
ent with  iron,  or  with  iron  and  a  moderate  proportion  of  alumin- 
ium. If,  however,  the  amount  of  aluminium  is  large  in  propor- 
tion to  the  iron,  it  is  difficult  to  precipitate  it  completely  with 
sodium  acetate.  Instead  of  precipitating  manganese  with 
ammonium  sulphide  it  may  be  separated  from  calcium  and 
magnesium  by  precipitation  with  bromine.  Add  aqueous  solu- 
tion of  bromine  to  the  filtrate  from  the  iron  precipitate  with- 
out previous  concentration  of  the  filtrate,  unless  its  volume 
exceeds  600  or  700  c.c.,  and  proceed  according  to  §  159,  62.] 

3.  Method  framed  upon  the  application  of  Ammonium  Sul- 
phide. 

Mix  the  fluid  in  a  flask  with  ammonium  chloride,  then  with  88 
ammonia,  until  a  precipitate  just  begins  to  form,  then  with 
yellow  ammonium  sulphide,  fill  the  flask  nearly  up  to  the  top 
with  water,  cork  it,  allow  to  settle  in  a  warm  place,  filter,  and 
wash  the  precipitate — consisting  of  iron  and  manganese  sulphides 
and  aluminium  hydroxide — without  interruption  with  water 
containing  ammonium  sulphide.  Separate  the  calcium,  magne- 
sium, and  alkalies  in  the  filtrate  as  in  87.  Dissolve  the  precipi- 


532  .SEPARATION.  [§  1(U. 

tate  in  hydrochloric  acid,  and  separate  the  aluminium  from  the 
iron  and  manganese  according  to  65  or  66,  and  then  the  iron 
from  the  manganese,  say  by  70  or  71. 

The  following  method  is  particularly  suitable  in  cases  where 
no  manganese  is  present,  or  only  inappreciable  traces : 

4.  Method  based  upon  the  application  of  Ammonia. 

The  solution  must  contain  all  the  iron  in  the  state  of  a  ferric  89 
salt.  Add  a  relatively  large  quantity  of  ammonium  chloride, 
and — observing  the  precautions  indicated  in  37 — precipitate 
with  ammonia.  The  precipitate  contains  the  whole  of  the  iron 
and  aluminium ;  at  most  an  inappreciable  amount  of  the  latter 
remains  in  solution  if  the  free  ammonia  has  been  almost  but 
not  entirely  driven  off  by  heat,  if  the  solution  was  diluted  suffi- 
ciently, and  if  enough  ammonium  chloride  was  present.  It 
may  also  contain  small  quantities  of  calcium  and  magnesium 
and  a  little  manganese.  It  is  well,  therefore,  usually  to  redis- 
solve  the  washed  precipitate  in  hydrochloric  acid,  and  reprecipi- 
tatc  with  ammonia.  In  this  way  the  precipitate  will  be  got  free 
from  alkali-earths  and  manganese.  Wash  the  precipitate  com- 
pletely, dry,  ignite,  and  treat  according  to  87.  If  silicic  acid 
remains  undissolved,  it  is  to  be  determined  and  deducted.  The 
solution  filtered  from  the  aluminium  and  ferric  hydroxide  is 
concentrated  by  evaporation,  the  manganese  is  precipitated  and 
determined  according  to  §  109,  2,  as  sulphide,  the  alkali-earth 
metals  and  alkalies  in  the  filtrate  are  determined  according  to 
87.  The  weighed  sulphide  of  manganese  is  digested  with  dilute 
hydrochloric  acid,  any  residue  that  may  remain  fused  with 
bisulphate  of  potassa,  dissolved  in  water,  and  tested  for  alumina. 

Supplement  to  the  Fourth  Group. 
To  §§  158,  159,  160. 

SEPARATION  OF  URANIUM  FROM  THE  OTHER  METALS  OF 
GROUPS  I. — IY. 

It  has  already  been  stated,  in  §  114,  that  uranium  in  uranyl  90 
compounds  cannot  be  completely  separated  from  the  alkalies 
by  means  of  ammonia,  as  the  precipitated  ammonium  uranate 
is  likely  to  contain  also  fixed  alkalies.     The  precipitate  should 
therefore  be  dissolved  in  hydrochloric  acid,  the  solution  evapo- 


BASES    OF   GROUP   IV.  533 

rated  in  the  platinum  crucible,  the  residue  gently  ignited  in  a 
current  of  hydrogen  gas,  the  chlorides  of  the  alkali  metals 
extracted  with  water,  and  the  uranous  oxide  (U()a)  ignited  in 
hydrogen,  in  order  to  its  being  weighed  as  such,  or  in  the  air, 
whereby  it  is  converted  into  uranous  uranate,  U(UO4)S.  Instead 
of  dissolving  the  precipitate  in  hydrochloric  acid  and  treating 
the  solution  as  directed,  you  may  heat  the  precipitate  cau- 
tiously* with  ammonium  chloride,  and  treat  the  residue  with 
water  (H.  ROSE).  Uranium  may  be  completely  separated  from 
the  alkalies  also  by  ammonium  sulphide  as  II.  ROSE  found. 
REMELEf  has  examined  this  subject  with  great  care  and  recom- 
mends the  following  method  of  precipitation: — The  solution 
being  neutral  or  slightly  acid,  add  an  excess  of  yellow  ammo- 
nium sulphide  and  keep  nearly  boiling  for  an  hour  to  convert 
the  lirst  formed  precipitate  of  uranium  oxy sulphide  entirely 
into  a  mixture  of  uranous  oxide  and  sulphur.  The  fluid,  at  first 
dark  from  presence  of  dissolved  uranium,  will  now  appear  yel- 
low and  transparent.  Filter  off  the  precipitate  containing  all 
the  uranium  and  wash  it  with  cold  or  warm  water,  first  by 
decantation,  finally  on  the  filter.  It  is  well  to  mix  a  little 
ammonium  sulphide  or  chloride  with  the  water,  as  when  pure 
water  is  used  the  last  filtrate  is  apt  to  be  turbid.  The  dried 
precipitate  is  roasted  and  then  converted  into  uranous  uranate 
by  ignition  in  the  air,  or  into  uranous  oxide  by  ignition  in 
hydrogen  (§  114). 

From  barium  uranyl  may  be  separated  by  sulphuric  acid,  91 
from  strontium  and  calcium  by  sulphuric  acid  and  alcohol. 
Ammonia  fails  to  effect  complete  separation  of  uranyl  from  the 
alkali-earth  metals,  the  precipitate  always  containing  not  incon- 
siderable quantities  of  the  latter.  In  such  precipitates,  however, 
the  uranium  and  the  alkali-earth  metals  may  likewise  be  sepa- 
rated by  gentle  ignition  with  ammonium  chloride  and  treatment 
of  the  residue  with  water. 

Uranyl  may  be  separated  from  strontium  and  calcium  also  92 
by  precipitation  with  ammonium  sulphide  by  the  method  given 
above  in  the  separation  from  the  alkalies.     As  carbonates  of  the 
alkali-earth  metals  may  be  coprecipitated,  treat  the  washed  pre- 


*  Strong  ignition  would  occasion  the  volatilization  of  uranium  chloride, 
f  Zeitschr.  f.  anal.  Chem.  4,  379. 


534  SEPARATION.  [§  161. 

cipitate  of  uranous  oxide  ancl  sulphur  in  the  cold  with  dilute 
hydrochloric  acid  which  will  not  dissolve  uranous  oxide. 
Ammonium  sulphide  will  not  answer  for  the  separation  of 
uranium  from  barium  (REMELE*). 

Magnesium  may  be  separated  from  uranyl  not  only  by  93 
ammonium  sulphide  in  presence  of  ammonium  chloride,  but 
also  by  ammonia.  Add  enough  ammonium  chloride  to  the 
solution,  heat  to  boiling,  supersaturate  with  ammonia,  continue 
boiling  till  the  odor  of  ammonia  is  but  slight,  filter  the  hot  fluid, 
and  wash  the  precipitate,  which  is  free  from  magnesium,  with 
hot  water  containing  ammonia  (H.  ROSE).  It  is  always  well  to 
test  the  uranous  oxide  obtained  by  ignition  in  hydrogen  for 
magnesium  by  treating  with  dilute  hydrochloric  acid. 

Aluminium  is  best  separated  from  uranyl  by  mixing  the 
somewhat  acid  fluid  with  ammonium  carbonate  in  excess.  The 
uranyl  passes  completely  into  solution,  while  the  aluminium 
remains  absolutely  undissolved.  Filter,  evaporate,  add  hydro- 
chloric acid  to  resolution  of  the  precipitate  produced,  heat  till 
all  the  carbonic  acid  is  expelled,  and  precipitate  with  ammonia 
(§  H4). 

Uranyl  is  best  separated  from  chromium  (W.  GiBBsf)  by 
adding  to  the  solution  soda  in  slight  excess,  heating  to  boiling 
and  adding  bromine  water,  when  the  chromium  is  rapidly 
converted  into  chromic  acid.  Filter  the  solution  containing 
sodium  chromate  from  the  precipitate  which  has  a  deep  orange- 
red  color  and  consists  of  a  compound  of  soda  and  uranic  oxide 
mixed  with  some  uranyl  chromate.  Wash  the  precipitate  with 
hot  water  containing  a  little  soda,  dissolve  it  in  hot  nitric  acid, 
boil  the  solution  a  few  minutes  to  drive  off  any  nitrous  acid,  and 
precipitate  the  chromic  acid  according  to  §  130,  I.,  a,  ft  with 
mercurous  nitrate  (according  to  GIBBS  at  a  boiling  heat).  The 
filtrate  now  contains  the  whole  of  the  uranium,  of  course  in 
presence  of  mercury. 

The  separation  of  uranyl  from  the  metals  of  the  fourth  94 
group  may  be  based  simply  on  the  fact  that  ammonium  carbonate 
prevents  the  precipitation  of  uranyl,  but  not  that  of  the  other 
metals   by   ammonium   sulphide.     Mix   the    solution   with   a 
mixture  of  ammonium  carbonate  and  ammonium  sulphide,  allow 


*  Zeitschr.  f.  anal.  Chem.  4,383.  \  Ib.  12,  310. 


§  161.]  BASES   OF   GROUP  IV.  535 

to  subside  in  a  closed  flask,  and  wash  the  precipitate  with  water 
containing  ammonium  carbonate  and  ammonium  sulphide. 

Remove  the  greater  part  of  the  excess  of  ammonium  car- 
bonate from  the  filtrate  by  a  very  gentle  heat,  acidify  with 
hydrochloric  acid,  warm,  filter  off  the  separated  sulphur,  and 
throw  down  the  uranium  either  by  ammonium  sulphide  (see 
above,  Separation  of  Uranium  from  the  Alkalies)  or  by 
heating  with  nitric  acid  and  then  adding  ammonia  (H.  ROSE,* 
REMELE-T).  The  method  is  not  so  suitable  in  presence  of  nickel, 
as  a  little  of  this  metal  is  very  liable  to  pass  into  the  filtrate 
on  precipitation  with  ammonium  carbonate  and  ammonium 
sulphide. 

Ferric  iron  may  be  also  separated  from  uranyl  by  means  of 
an  excess  of  ammonium  carbonate.  '  The  small  quantity  of  iron 
which  passes  with  the  uranium  into  solution  will  fall  down  on 
allowing  the  solution  to  stand  for  several  hours,  or  it  may  be 
precipitated  with  ammonium  sulphide,  before  the  uranium  is 
thrown  down  (PisA^i^:). 

From  nickel,  cobalt,  manganese,  zinc,  and  magnesium 
the  urauyl  may  also  be  separated  by  barium  carbonate.  The 
fluid,  which  should  contain  a  little  free  acid,  is  mixed  with  the 
precipitant  in  excess,  and  allowed  to  stand  in  the  cold  for  24 
hours  with  frequent  shaking  (64). 

From  cobalt,  nickel,  and  zinc  uranyl  may  also  be  separated  95 
(GIBBS  and  PERKINS§)  by  taking  the  neutral  or  slightly  acid 
solutions  of  the  chlorides,  adding  sodium  acetate  in  excess  and 
a  few  drops  of  acetic  acid,  and  passing  a  rapid  current  of  hydro- 
gen sulphide  for  half  an  hour  through  the  boiling  fluid.  The 
uranium  remains  dissolved  while  the  other  metals  are  precipi- 
tated. ,  I  should  advise  testing  the  filtrate  with  a  mixture  of 
ammonium  carbonate  and  ammonium  sulphide  to  see  if  any 
nickel,  cobalt,  or  zinc  remain  in  solution. 


*  Zeitschr.  f.  anal.  Chem.  1,  412.  J  Compt.  rend.  52,  106. 

f  Ib.  4,  385.  §  Zeitschr.  f.  anal.  Chem.  3,  334. 


536  SEPARATION.  [§  162. 

Fifth  Group. 

SILVER — MERCURY  (iN  MERCUROUS  AND  MERCURIC  COMPOUNDS) — LEAD 
— BISMUTH COPPER CADMIUM. 

I.  SEPARATION  OF  THE  METALS  OF  THE  FIFTH  GROUP  FROM  THOSE 

OF   THE    FIRST    FOUR    GROUPS. 

§162. 

INDEX.     (The  numbers  refer  to  those  in  the  margin.) 

Silver  from  the  metals  of  Groups  I.— IV.,  96,  97. 
Mercury  (in  mercurous  and  mercuric  compounds)  from  the 

metals  of  Groups  I.— IV.,  96,  98. 
Lead  from  the  metals  of  Groups  I. — IV.,  96,  99. 
Bismuth  from  the  metals  of  Groups  I. — IV.,  96,  104. 
Copper  from  the  metals  of  Groups  I.— IV.,  96,  100,  101,  102. 

zinc,  103. 

Cadmium  from  the  metals  of  Groups  I. — IV.,  96. 
zinc,  105. 

A.     General  Method. 

ALL  THE  METALS  OF  THE  FIFTH  GROUP  FROM  THOSE  OP 
THE  FIRST  FOUR  GROUPS. 

Principle :  Hydrogen  Sulphide  precipitates  from  Acid 
Solutions  the  Metals  of  the  Fifth  Group,  but  not  those  of  the 
first  Four  Groups. 

The  following  points  require  especial  attention  in  the  execu- 
tion of  the  process : 

of.  To  effect  the  separation  of  the  metals  of  the  fifth  group  96 
from  those  of  the  first  three  groups,  by  means  of  hydrogen 
sulphide,  it  is  necessary  simply  that  the  reaction  of  the  solution 
should  be  acid,  the  nature  of  the  acid  to  which  the  reaction  is 
due  being  of  no  consequence.  But,  to  effect  the  separation  of 
the  metals  of  the  fifth  group  from  those  of  the  fourth,  the 
presence  of  a  free  mineral  acid  is  indispensable  ;  otherwise  zinc 
and,  under  certain  circumstances,  also  cobalt  and  nickel  may  be 
coprecipitated. 

/?.  But  even  the  addition  of  hydrochloric  acid  to  the  fluid 
will  not  always  entirely  prevent  the  coprecipitation  of  the  zinc. 
RIVOT  and  BOUQUET*  declare  a  complete  separation  of  copper 

*  Annal.  d.  Chem.  u.  Pharm.  80,  364. 


§  162.]  BASES   OF   GROUP   V.  537 

from  zinc  by  means  of  hydrogen  sulphide  altogether  imprac- 
ticable. CALVEKT  *  states  that  he  has  arrived  at  the  same  con- 
clusion. On  the  other  hand,  SriRGATist  concurs  with  H.  ROSE 
in  maintaining  that  the  complete  separation  of  copper  from  zinc 
may  be  effected  by  means  of  hydrogen  sulphide  in  presence  of 
a  sufficient  quantity  of  free  acid. 

In  this  conflict  of  opinions,  I  thought  it  necessary  to  subject 
this  method  once  more  to  a  searching  investigation.  I  there- 
fore instructed  one  of  the  students  in  my  laboratory,  Mr. 
GRUNDMANX,  to  make  a  series  of  experiments  in  the  matter, 
with  a  view  to  settling  the  question.  + 

The  following  process  is  founded  on  the  results  which  we 
obtained  : 

Add  to  the  COPPER  and  ZINC  solution  a  large  amount  of 
hydrochloric  acid  (e.g.^  to  -4  grm.  oxide  of  copper  in  250  c.c.  of 
solution,  30  c.c.  hydrochloric  acid  of  I'l  sp.  gr.),  conduct  into 
the  fluid  at  about  70°  hydrogen  sulphide  largely  in  excess,  filter 
before  the  excess  of  hydrogen  sulphide  has  had  time  to  escape 
or  become  decomposed,  wash  with  hydrogen  sulphide  water, 
dry,  roast,  redissolve  in  nitrohydrochloric  acid,  evaporate  nearly 
to  dryness,  add  water  and  hydrochloric  acid  as  above,  and  pre- 
cipitate again  with  hydrogen  sulphide.  This  second  precipi- 
tate is  free  from  zinc ;  it  is  treated  as  directed  in  §  119,  3. 

If  CADMIUM  is  present,  it  is  well  to  have  less  acid  present, 
e.g.,  to  '±  grm.  oxide  of  cadmium  in  250  c.c.  of  solution  add  10 
c.c.  hydrochloric  acid  of  I'l  sp.  gr.  If  the  quantity  of  zinc  is 
considerable,  dissolve  the  first  precipitate  of  cadmium  sulphide 
in  hot  hydrochloric  acid,  evaporata  nearly  to  dryness,  add  10 
c.c.  hydrochloric  acid  and  about  250  c.c.  water,  and  precipitate 
again.  In  this  way  the  results  are  quite  satisfactory. 

y.  The  other  metals  of  the  fifth  group  comport  themselves 
in  this  respect  similarly  to  cadmium,  i.e.,  they  are  not  com- 
pletely precipitated  by  hydrogen  sulphide  in  presence  of  too 
much  free  acid  in  a  concentrated  solution.  Lead  requires  the 
least  amount  of  free  acid  to  be  retained  in  solution ;  then  follow 
in  order  of  succession,  cadmium,  mercury,  bismuth,  copper,  sil- 
ver (M.  MARTIN§).  A  portion  of  the  filtrate  should,  if  neces- 


*  Journ.  f.  prakt.  Chem.  71,  155.  \  Ib.  73,  241. 

f  Ib.  57,  184.  §  Ib.  67,  371. 


538  SEPARATION.  [§  162. 

sary,  be  tested  by  addition  of  a  large  quantity  of  hydrogen  sul- 
phide to  see  if  the  precipitation  of  the  fifth  group  was  com- 
plete. 

d.  If  hydrochloric  acid  produces  no  precipitate  in  the 
solution,  it  is  preferred  as  acidifying  agent,  otherwise  sulphuric 
or  nitric  acid  must  be  used.  In  the  latter  case  the  fluid  must 
be  rather  largely  diluted.  ELIOT  and  STOKER  *  arrived  at  the 
same  conclusion  as  ourselves,  and  showed  that  the  cause  of 
CAL VERT'S  unfavorable  results  was  the  too  large  dilution  of  his 
solutions.  For  to  prevent  the  precipitation  of  zinc  you  have 
not  merely  to  preserve  a  certain  proportion  between  the  zinc 
and  the  free  acid,  but  also  a  certain  degree  of  dilution. 
Although  I  agree  with  the  above-named  chemists  in  the  opinion 
that  it  is  possible  to  produce  a  condition  of  the  fluid,  under 
which  one  precipitation  will  effect  complete  separation,  still  it 
appears  to  me  better,  for  practical  purposes,  to  precipitate  twice, 
as  this  is  sure  to  lead  to  the  desired  result. 

£.  A  somewhat  copious  experience  in  the  separation  of  COP- 
PER from  NICKEL  (and  COBALT)  which  so  frequently  occurs  has 
led  me  to  the  opinion  that  a  double  precipitation  is  unnecessary. 
If  the  solution  which  is  to  be  treated  with  hydrogen  sulphide 
contains  enough  free  hydrochloric  acid  and  not  too  much  water, 
the  copper  falls  down  absolutely  free  from  nickel,  while,  on  the 
other  hand,  if  the  quantity  of  free  acid  is  not  too  large,  the  fil- 
trate will  be  quite  free  from  copper. 

£.  CADMIUM  and  ZINC  may,  according  to  FOLLENIUS,  also  be 
completely  separated  by  a  single  precipitation,  if  the  metals  are 
present  in  a  sulphuric  acid  solution  containing  25  or  30  per 
cent,  of  dilute  acid  of  1-19  sp.  gr.  Precipitate  with  hydrogen 
sulphide  at  70°.  Collect  the  precipitate  on  a  weighed  asbestos 
filter,  dry  in  a  current  of  heated  air,  ignite  gently  in  a  stream 
of  pure  hydrogen  sulphide  (to  convert  small  quantities  of  cad- 
mium sulphate  into  sulphide),  remove  the  small  quantity  of 
separated  sulphur  by  gentle  ignition  in  a  current  of  air,  and 
weigh. 


*  On  the  Impurities  of  Commercial  Zinc,  &c. — Memoirs  of  the  American 
Academy  of  Arts  and  Sciences.     New  Series.     Vol.  8. 


§  162.]  BASES   OF   GROUP  V.  539 

B.  Special  Methods. 

SINGLE  METALS  OF  THE  FIFTH  GROUP  FROM  SINGLE  OR 
MIXED  METALS  OF  THE  FIRST  FOUR  GROUPS. 

1.  SILVER  is  most  simply  and  completely  separated  from  the  97 
METALS  OF  THE  FIRST  FOUR  GROUPS  by  means  of  hydrochloric 
acid.     The  hydrochloric  acid  must  not  be  used  too  largely  in 
excess,  and  the  fluid  must  be  sufficiently  dilute ;  otherwise  a 
portion  of  the  silver  will  remain  in  solution.     Care  must  be 
taken  also  not  to  omit  the  addition  of  nitric  acid,  which  pro- 
motes the  separation  of  the  silver  chloride.     The  latter  should 

be  treated  according  to  §  115,  1,  a. 

2.  The  separation  of  MERCURY  from  the  METALS  OF  THE  98 
FIRST  FOUR  GROUPS  may  be  effected  also  by  ignition,  which  will 
cause  the  volatilization  of  the  mercury  or  the  mercurial  com- 
pound, leaving  the  non-volatile  bodies  behind.     The  method  is 
applicable  in  many  cases  to  alloys,  in  others  to  oxides,  chlorides, 

or  sulphides.  If  the  mercury  is  estimated  only  from  the  loss, 
the  operation  is  conducted  in  a  crucible ;  otherwise  in  a  bulb- 
tube,  or  a  wide  glass  tube  with  porcelain  boat.  In  the  latter 
case  it  is  well  to  use  a  current  of  hydrogen  (compare  §  118, 

i,«). 

The  precipitation  of  mercury  as  mercurous  chloride  with 
phosphorous  acid,  according  to  §  118,  2,  is  also  well  adapted  for 
its  separation  from  metals  of  the  first  four  groups.  If  the  mer- 
cury is  already  present  as  a  mercurous  salt,  it  may  be  separated 
and  determined  in  a  simple  manner,  by  precipitation  with 
hydrochloric  acid  (§  117,  1). 

3.  FROM  THOSE  BASIC  RADICALS  WHICH  FORM  SOLUBLE  SALTS  99 
WITH  SULPHURIC  ACID,  LEAD  may  be  readily  separated  by  that 
acid.     The  results  are  very  satisfactory,  if  the  rules  given  in 

§  116,  3  are  strictly  adhered  to. 

If  you  have  lead  in  presence  of  barium,  both  in  form  of 
sulphates,  digest  the  precipitate  with  a  solution  of  ordinary 
ammonium  sesquicarbonate,  without  application  of  heat.  This 
decomposes  the  lead  salt,  leaving  the  barium  salt  unaltered. 
Wash,  first  with  solution  of  ammonium  carbonate,  then  with 
water,  and  separate  finally  the  lead  carbonate  from  the  barium 
sulphate,  by  acetic  acid  or  dilute  nitric  acid  (H.  HOSE*).  The 

*  Journ.  f.  prakt.  Cbem.  66,  166. 


540  SEPARATION.  [§  102. 

same  object  may  also  be  attained  by  suspending  the  washed 
insoluble  salts  in  water  and  digesting  with  a  clear  concentrated 
solution  of  sodium  thiosulphate  at  15 — 20°  (not  higher).  The 
barium  sulphate  remains  undissolved,  the  lead  sulphate  dis- 
solves. Determine  the  lead  in  the  nitrate  (after  §  110,  2)  as 
lead  sulphide  (J.  LOWE*). 

4.    (  1OPPER  FROM  ALL  METALS  OF  THE  FIRST  FoUR  GROUPS. 

a.  Free  the  solution  as  far  as  possible  from  hydrochloric  100 
and  nitric  acids  by  evaporation  with  sulphuric  acid.  Dilute  if 
necessary,  boil,  and  add  sodium  thiosulphate  f  as  long  as  a  black 
precipitate  continues  to  form.  As  soon  as  this  lias  deposited, 
and  the  supernatant  fluid  contains  only  suspended  sulphur, 
the  whole  of  the  copper  is  precipitated.  The  precipitate  is 
cuprous  sulphide  (Cu2S),  and  may  be  readily  washed  without 
suffering  oxidation.  Convert  it  into  anhydrous  cuprous  sul- 
phide by  ignition  in  hydrogen  (§  119,  3).  The  other  metals 
are  in  the  nitrate  and  washings.  Evaporate  with  some  nitric 
acid,  filter,  and  determine  the  metals  in  the  filtrate.  \  Results 
good.  The  method  requires  practice,  as  the  end  of  the  pre- 
cipitation of  the  copper  is  not  so  easy  to  hit  as  when  hydro- 
gen sulphide  is  employed. 

If  the  solution  contained  hydrochloric  or  nitric  acid,  and 
this  was  not  first  removed  before  the  addition  of  the  thiosul- 
phate, the  precipitant  would  be  required  in  much  larger  quan- 
tity ;  in  the  presence  of  hydrochloric  acid  because  the  cuprous 
chloride  produced  is  only  decomposed  by  a  large  excess  of 
thiosulphate,  in  the  presence  of  nitric  acid  because  the  thio- 
sulphate does  not  begin  to  act  on  the  copper  salt  till  all  the 
nitric  acid  is  decomposed. 

*Journ.  f.  prakt.  Chem. 

f  The  commercial  salt  is  often  not  sufficiently  pure ;  in  which  case  some 
sodium  carbonate  must  be  added  to  its  solution,  and  the  mixture  filtered. 

\  As  far  back  as  1842,  C.  HTMLY  made  the  first  proposal  to  employ  sodium 
thiosulphate  for  the  precipitation  of  many  metals  as  sulphides  (Annul,  d.  Chem. 
u.  Pharm.  43,  150).  The  question,  after  long  neglect,  was  afterwards  taken  up 
again  by  VOHL  (Annal.  d.  Chem.  u.  Pharm.  96,  237),  and  SLATER  (Chem.  Gaz. 
1855,  369).  FLAJOLOT,  however,  made  the  first  quantitative  experiment  (Annal. 
des.  Mines,  1853,  641 ;  Journ.  f .  prakt.  Chem.  61,  105).  The  results  obtained  by 
him  are  perfectly  satisfactory. 


§  162.]  BASES   OF   GROUP  V.  541 

~b.  Precipitate  the  copper  as  cuprous  sulphocyanate  accord-  101 
ing  to  §  119,  3,  b ;  the  other  metals  remain  in  solution  (Rrvor). 
If  alkalies  were  present  and  it  were  desired  to  determine  them 
in  the  filtrate,  ammonium  sulphocyanate  must  be  used  instead 
of  the  potassium  salt  usually  employed.  This  method  is  par- 
ticularly well  adapted  for  the  separation  of  copper  from  zinc. 
The  zinc  can  be  precipitated  at  once  from  the  filtrate  by  sodium 
carbonate.  The  method  is  also  suitable  for  separating  copper 
from  iron  (EL  ROSE*)  ;  in  this  case  it  is  unnecessary  that  ferric 
salts  be  completely  reduced  by  the  sulphurous  acid  added ;  the 
separation  may  be  effected,  even  if  the  solution  becomes  blood- 
red  on  the  addition  of  the  precipitant. 

c.  The  solution  should  be  free  from  hydrochloric  acid,  and  102 
should  contain  a  certain  quantity  of  free  nitric  acid  (20  c.c. 
nitric  acid  of  1*2  sp.  gr.  to  200  c.c.),  and  some  sulphuric  acid. 
Throw  clown  the  copper  by  a  galvanic  current,  so  that  the 
met :il  may  be  firmly  deposited  on  a  platinum  vessel  (prefer- 
ably a  platinum  cone),  which  forms  the  negative  pole.  Take 
care  that  the  current  is  strong  enough,  and,  without  interrupt- 
ing it,  remove  the  cone  from  the  fluid  occasionally  to  see  when 
the  copper  is  all  precipitated.  With  proper  execution  the 
separation  of  copper  from  all  metals  of  Groups  1-4  is  thorough. 
All  metals  of  Groups  1-4  remain  dissolved,  except  manganese, 
which  separates  as  binoxide  at  the  positive  pole.  The  method 
requires  practice  and  strict  attention  to  the  conditions  which 
have  been  determined  by  a  long  course  of  experiments.  It  is 
particularly  suited  for  mining  assays  and  manufactures.  The 
electrolytic  method  of  separating  copper  was,  I  believe,  first 
recommended  by  GiBBS,f  and  afterwards  improved  by 
LECOQ  DE  BoiSBArDKAx,§  ULLGREN,||  and  MER- 
^  have  also  written  on  this  subject.  Finally  the  method 
was  very  accurately  and  minutely  described  by  the  Mansfelder 
Ober-Berg-  und  Hiittendirection  at  Eisleben,**  who,  after 
giving  a  prize  to  LUCKOW'S  method,  afterwards  adopted  it,  and 
still  further  improved  it.  I  must  refer  the  reader  for  details 
to  the  last  mentioned  memoir  and  LUCKOW'S  paper. 

*  Pogg.  Annal.  110,  424.  f  Zeitschr.  f.  anal.  Chern.  3,  334. 

t  Dingler's  polyt.  Journ.  177,  296,  and  (in  detail)  Zeitschr.  f.  anal.  Chem.  8,  25. 

§  Zeitschr.  f .  anal.  Chem.  7,  253,  and  9,  102.  |  Ib.  7,  255. 

*"  American  Chemist,  2,  136.  **  ^eitschr.  f.  anal.  Chem.  11,  1. 


542  SEPARATION.  [§  162. 

COPPER  FROM  ZINC. 

BOBIERRE*  employed  the  following  method  with  satisfac-  IDS 
tory  results  in  the  analysis  of  many  alloys  of  zinc  and  copper : 
The  alloy  is  put  into  a  porcelain  boat  lying  in  a  porcelain  tube, 
and  heated  to  redness  for  three-quarters  of  an  hour  at  the 
most,  a  rapid  stream  of  hydrogen  gas  being  conducted  over  it 
during .  the  process.  The  zinc  volatilizes,  the  copper  remains 
behind.  If  the  alloy  contains  a  little  lead  (under  2  to  3  per 
cent.)  this  goes  off  entirely  with  the  zinc,  and  is  partly  depos- 
ited in  the  porcelain  tube  in  front  of  the  boat ;  if  more  lead 
is  present  part  only  is  volatilized,  the  rest  remaining  with  the 
copper  (M.  BuRSTYNf). 

6.  BISMUTH  FROM  THE  METALS  OF  THE  FIRST  FOUR  GROUPS, 
WITH  THE  EXCEPTION  OF  FERRIC  IRON. 

Precipitate  the  bismuth  according  to  §  120, 4,  as  basic  chlo-  104 
ride,  and  determine  it  as  metal ;  all  the  other  basic  metals 
remain  completely  in  solution.     Results  very  satisfactory  (H. 
ROSE}). 

7.  CADMIUM  FROM  ZINC. 

Prepare  a  hydrochloric  or  nitric  acid  solution  of  the  two  105 
oxides,  as  neutral  as  possible,  add  a  sufficient  quantity  of  tar- 
taric  acid,  then  solution  of  potassa  or  soda,  until  the  reaction  of 
the  clear  fluid  is  distinctly  alkaline.  Dilute  now  with  a  suffi- 
cient quantity  of  water,  and  boil  for  1-J— 2  hours.  All  the  cad- 
mium precipitates  as  hydroxide,  free  from  alkali  (to  be  deter- 
mined as  directed  §  121),  whilst  the  whole  of  the  zinc  remains 
in  solution  ;  the  latter  metal  is  determined  as  directed  in  §  108, 
1, 1}  (AUBEL  and  RAMDOHR§).  The  test-analyses  communicated 
are  satisfactory.  As  the  separation  only  succeeds  when  the  sub- 
stances are  present  in  correct  proportions,  I  will  add  the  quan- 
tities employed  by  AUBEL  and  RAMDOHR  with  especially  good 
effect.  About  1  grrn.  oxide  of  zinc  and  1  grm.  oxide  of  cad- 
mium were  dissolved  in  hydrochloric  acid,  30  grm.  solution 
of  tartaric  acid  (containing  -23  grm.  acid  in  1  grin.),  50  grm. 
soda  solution  of  1-16  sp.  gr.,  and  120  grm.  water  added,  and 
the  whole  boiled  2  hours.  (The  boiling  must  on  no  account 
be  done  in  glass ;  a  platinum  or  silver  dish  should  be  used.) 


*  Compt.  rend.  36,  224;  Journ.  f.  prakt.  Chern.  58,  380. 

f  Zeitschr.  f.  anal.  Chem.  11,  175. 

\  Pogg.  Annal.  110,  429.  §  Annal.  d.  Chem.  u.  Pharm.  103,  33. 


§  163.]  BASES   OF   GKOUP   V.  543 


II.    SEPARATION    OF   THE  METALS   OF   THE   FIFTH   GROUP 

EACH    OTHER.* 


INDEX.     (The  numbers  refer  to  those  in  the  margin.) 

Silver  from  copper,  106,  111,  113,  124,  125. 
cadmium,  106,  111,  113. 
bismuth,  106,  110,  113,  122. 
mercuricura,*  106,  111,  113,  119,  121. 
lead,  106,  109,  110,  113,  124. 
Mercuricum*  from  silver,  106,  111,  113,  119,  121. 
mercurosurn,*  107. 
lead,  108,  109,  110,  113,  119,  121. 
bismuth,  108,  110,  113,  114,  119. 
copper,  108,  112,  113,  119,  121. 
cadmium,  108,  113,  119. 
Mercurosum*  from  mercuricum,  107. 
copper,  107. 
cadmium,  107. 
lead,  107,  109. 

Compare  also  raercuricum  from  other  metals. 
Lead  from  silver,  106,  110,  113,  124,  125. 

mercuricum,  108,  109,  110,  113,  119,  121. 
"          mercurosum,  107,  109. 

copper,  109,  110,  113,  115. 
bismuth,  109,  115,  122,  123. 
cadmium,  109,  110,  113. 
Bismuth  from  silver,  106,  110,  113,  122. 
lead,  109,  115,  122,  123. 
copper,  110,  113,  114,  116,  122. 
cadmium,  110,  113;  114,  115,  118. 
mercuricum,  108,  110,  113,  114,  119. 
Copper  from  silver,  106,  111,  113,  124. 
lead,  109,  110,  113,  115. 
bismuth,  110,  113,  114,  116,  122. 
mercuricum,  108,  112,  113,  119,  121. 
mercurosum,  107. 
cadmium,  112,  113,  117,  120. 

Copper  in  cupric  from  copper  in  cuprous  compounds,  135. 
Cadmium  from  silver,  106,  111,  113. 
lead,  109,  110,  113. 
bismuth,  110.  113,  114,  115,  118. 
copper,  112,  113,  115,  117,  120. 
mercuricum,  108,  113,  119. 
mercurosum,  107. 

*  For  the  sake  of  brevity  the  terms  "  mercuricum"  and  "mercurosum"  are 
Used  to  designate  respectively  mercury  in  mercuric  and  mercurous  compounds. 


544  SEPARATION.  [§  163. 

1.  Methods  based  upon  the  Insolubility  of  certain  of  the 
Chlorides  in  Water  or  Alcohol. 

a.  SILVER  FROM  COPPER,  CADMIUM,  BISMUTH,  MERCURICUM,  AND 
LEAD. 

a.  To  separate  silver  from  copper,  cadmium,  and  bismuth,  106 
add  to  the  nitric  acid  solution  containing  excess  of  nitric  acid, 
hydrochloric  acid  as  long  as  a  precipitate  forms,  and  separate 
the  precipitated  silver  chloride  from  the  solution  which  con- 
tains the  other  metals,  as  directed  §  115,  1,  a.     In  the  presence 
of  bismuth,  after  pouring  off  the  supernatant  fluid,  heat  again" 
with  nitric  acid,  and  wash  with  dilute  nitric  acid  before  wash- 
ing with  water. 

ft.  If  you  wish  to  separate  mercuricum  from  silver  by 
hydrochloric  acid,  special  precautions  must  be  taken,  as  a  solu- 
tion of  mercuric  nitrate  possesses  the  property  of  dissolving 
silver  chloride  (WAOKENRODER,  v.  LIEBIG,*  IT.  DEBRAYf). 
Although  the  silver  chloride  in  solution  for  the  most  part 
separates  on  the  addition  of-  enough  hydrochloric  acid  to  con- 
vert the  mercuric  nitrate  into  chloride,  or  on  addition  of 
sodium  acetate,  still  we  cannot  depend  upon  the  complete  pre- 
cipitation of  the  silver.  On  this  account,  mix  the  nitric  acid 
solution — which  must  not  contain  any  mercurous  salt,  and  is 
to  be  in  a  sufficiently  dilute  condition  and  acidified  with  nitric 
acid — with  hydrochloric  acid,,  as  long  as  a  precipitate  forms. 
Allow  to  deposit,  filter  off  the  clear  fluid,  heat  the  precipitate 
—to  free  it  from  any  possibly  coprecipitated  basic  mercuric 
salts — with  a  little  nitric  acid,  add  water,  then  a  few  drops  of 
hydrochloric  acid,  and  filter  off  the  silver  chloride.  In  the 
filtrate  determine  the  mercury  as  sulphide  (§  118,  3),  and 
finally  test  this  for  silver,  by  ignition  in  a  stream  of  hydrogen 
— any  silver  that  may  happen  to  be  present  will  remain  behind 
in  the  metallic  state. 

y.  In  the  separation  of  silver  from  lead,  the  precipitation 
is  advantageously  preceded  by  addition  of  sodium  acetate. 
The  fluid  must  be  hot  and  the  hydrochloric  acid  rather  dilute ; 
no  more  must  be  added  of  the  latter  than  is  just  necessary. 
In  this  manner,  the  separation  may  be  readily  effected,  since 
.  . » 

*  Annal.  d.  Chem.  u.  Pliarm.  81,  128. 

f  Compt.  rend.  70,  847:  Zeitschr.  f.  anal.  Chem.  13,  349. 


§  163.]  BASES   OF   GROUP    V.  545 

lead  chloride  dissolves  in  sodium  acetate  (ANTHON).  The  sil- 
ver chloride  is  washed  with  hot  water.  The  lead  is  thrown 
down  from  the  nitrate  with  hydrogen  sulphide.  If  you  desire 
to  prevent  the  occasionally  injurious  influence  of  sodium  ace- 
tate, great  care  must  be  given  to  the  washing  of  the  silver 
chloride.  It  is  also  well  to  reduce  the  weighed  chloride  by 
gentle  ignition  in  a  current  of  hydrogen,  and  to  test  the  silver 
obtained  for  lead. 

d.  The  volumetric  method  (§  115,  5)  is  usally  resorted  to  in 
mints  to  determine  the  silver  in  alloys.  In  presence  of  a  mer- 
curic salt,  sodium  acetate  is  mixed  with  the  fluid,  immediately 
before  the  addition  of  the  solution  of  chloride  of  sodium.  In 
the  East  India  mint  the  silver  is  separated  and  weighed  as 
chloride.* 

5.  MERCUROSUM  FROM  MERCURICUM,  COPPER,  CADMIUM,  AND 
LEAD. 

Mix  the  highly  dilute  cold  solution  with  hydrochloric  acid  107 
as  long  as  a  precipitate  (mercurous  chloride)  forms ;  allow  this 
to  deposit,  filter  on  a  weighed  filter,  dry  at  100°,  and  weigh. 
The  filtrate  contains  the  other  metals.  If  you  have  to  analyze 
a  solid  body,  insoluble  in  water,  either  treat  directly,  in  the 
cold,  with  dilute  hydrochloric  acid,  or  dissolve  in  highly  dilute 
nitric  acid,  and  mix  the  solution  with  a  large  quantity  of  water 
before  proceeding  to  precipitate.  Care  must  always  be  taken 
that  the  mode  of  solution  is  such  as  not  to  convert  mercurous 
into  mercuric  compounds.  If  lead  is  present  the  washing  of 
the  mercurous  chloride  must  be  executed  with  special  care 
with  water  of  60 — 70°,  till  the  filtrate  ceases  to  be  colored  with 
hydrogen  sulphide.  As  an  additional  security,  it  is  well  to 
test  at  last  whether  the  weighed  mercurous  chloride  leaves  no 
lead  sulphide  behind  on  cautious  ignition  with  sulphur  in  a 
stream  of  hydrogen. 

c.  MERCUROSUM  AND  MERCURICUM  FROM  COPPER,  CADMIUM, 
AND  (but  less  wrell)  FROM  BISMUTH  AND  LEAD. 

If  mercury  is  present  as  a  mercuric  compound,  or  partly  108 
in  a  mercuric  and  partly  in  a  mercurous  compound,  it  is  pre- 
cipitated according  to  §  118,  2,  by  means  of  hydrochloric  acid 

*  Chem.  Centralbl.  1872,  202. 


546  SEPARATION.  [§  163. 

and  phosphorous  acid  as  mercurous  chloride.  The  precipitate, 
particularly  when  bismuth  is  present,  is  first  washed  with  water 
containing  hydrochloric  acid,  then  with  pure  water,  till  the 
washings  are  no  longer  colored  with  hydrogen  sulphide  (H. 
HOSE*).  In  the  presence  of  lead,  the  remarks  in  107  must  be 
attended  to. 

2.   Methods  based  upon  the   Insolubility  of  Lead 
Sulphate. 

LEAD  FROM  ALL  OTHER  METALS  OF  THE  FIFTH  GROUP. 

Mix  the  nitric  acid  solution  with  pure  sulphuric  acid  in  not  109 
too  slight  excess,  evaporate  until  the  sulphuric  acid  begins  to 
volatilize,  allow  the  fluid  to  cool,  add  water  (in  which,  if  there 
is  a  sufficient  quantity  of  free  sulphuric  acid  present,  the  mer- 
curic and  bismuth  sulphates  dissolve  completely),  and  then 
filter  the  solution,  which  contains  the  other  metals,  without 
delay  from  the  undissolved  lead  sulphate.  If  it  is  feared  that 
the  residue  no  longer  contains  enough  free  sulphuric  acid,  add 
some  dilute  acid  to  it  before  adding  the  water.  Wash  the 
precipitate  with  water  containing  sulphuric  acid,  displace  the 
latter  with  alcohol,  dry,  .and  weigh  (§  116,  3).  Precipitate 
the  other  metals  from  the  filtrate  by  hydrogen  sulphide.  If 
silver  is  present  in  any  notable  quantity,  this  method  cannot 
be  recommended,  as  the  silver  sulphate  is  not  soluble  enough. 
In  this  case  you  may  follow  ELIOT  and  SrroRER,f  viz.,  mix  the 
solution  with  ammonium  nitrate,  warm,  precipitate  the  greater 
portion  of  the  silver  Avith  ammonium  chloride,  evaporate  the 
filtrate,  remove  the  ammonium  salts  by  ignition,  and  in  the 
residue  separate  the  small  remainder  of  the  silver  from  the 
lead  with  sulphuric  acid  as  just  directed.  For  the  separation 
of  lead  from  bismuth,  on  the  above  principle,  H.  ROSE:):  gives 
the  following  process  as  the  best.  If  both  oxides  are  in  dilute 
nitric  acid  solution,  as  is  usually  the  case,  evaporate  to  small 
bulk,  and  add  enough  hydrochloric  acid  to  dissolve  all  the 
bismuth ;  the  lead  separates  partially  as  chloride.  Should  a 
portion  of  the  clear  fluid  poured  off  become  turbid  on  the 
addition  of  a  drop  of  water,  you  must  add  some  more  hydro- 

*Pogg.  Annal.  110,  534. 

f  Proceedings  of  the  American  Academy  of  Arts  and  Sciences,  Sept.  11, 1860, 
p.  52;  Zeitschr.  f.  anal.  Chem.  1,  389. 


§  163.]  BASES    OF   GROUP  V.  547 

chloric  acid,  till  no  permanent  turbidity  is  produced  unless 
several  drops  of  water  are  added.  The  turbid  fluids  should 
all  be  returned,  and  the  glasses  rinsed  with  alcohol.  Add 
now  dilute  sulphuric  acid,  allow  to  stand  some  time  with  stir- 
ring, add  spirit  of  wine  of  -8  sp.  gr.,  stir  well,  allow  to  settle 
for  a  long  time,  filter,  wash  the  lead  sulphate  first  with  alco- 
hol mixed  with  a  small  quantity  of  hydrochloric  acid,  then 
with  pure  alcohol.  Determine  it  after  §  116,  3.  Mix  the 
filtrate  at  once  with  a  large  quantity  of  water,  and  proceed 
with  the  precipitated  basic  bismuth  chloride  according  to 
§  120,  4. 

3.   Methods  based  upon  different  depwtment  with 
Cyanide  of  Potassium  (FRESENIUS  and  HAIDLEN*). 

a.  LEAD  AND  BISMUTH  .FROM  ALL  OTHER  METALS  OF  THE 
FIFTH  GROUP. 

Mix  the  dilute  solution  with  sodium  carbonate  in  slight  110 
excess,  add  solution  of  potassium  cyanide  (free  from  sulphide), 
heat  gently  for  some  time,  filter  and  wash.  On  the  filter  you 
have  lead  and  bismuth  carbonates  (containing  alkali) ;  the  fil- 
trate contains  the  other  metals  as  cyanides  in  combination  with 
potassium  cyanide.  The  method  of  effecting  their  further 
separation  will  be  learnt  from  what  follows.  In  very  accurate 
analyses  bear  in  mind  that  the  filtrate  generally  contains  traces 
of  bismuth,  which  may  be  precipitated  by  ammonium  sulphide. 

b.  SILVER  FROM  MERCURICUM,  COPPER,  AND  CADMIUM. 

Add  to  the  solution,  which,  if  .it  contains  mur'h  free  acid,  111 
must  previously  be  nearly  neutralized  with  soda,  potassium 
cyanide  until  the  precipitate  which  forms  at  first  is  redissolved. 
The  solution  contains  the  cyanides  of  the  metals  in  combina- 
tion with  potassium  cyanide  as  soluble  double  salts.  Add 
dilute  nitric  acid  in  excess,  which  effects  the  decomposition  of 
the  double  cyanides ;  the  insoluble  silver  cyanide  precipitates 
permanently,  whilst  the  mercuric  cyanide  remains  in  solution, 
and  the  cyanides  of  copper  and  cadmium  redissolve  in  the 
excess  of  nitric  acid.  Treat  the  silver  cyanide  as  directed 
§  115,  3.  If  the  filtrate  contains  only  mercury  and  cadmium, 
precipitate  at  once  with  hydrogen  sulphide,  which  completely 

*  Annal.  d.  Chem.  u.  Pharm.  43,  129. 


548  SEPARATION.  .[§  163. 

throws  down  the  sulphides  of  the  two  metals ;  but  if  it  con- 
tains copper,  you  must  first  heat  with  sulphuric  acid,  until  the 
odor  of  hydrocyanic  acid  is  no  longer  perceptible,  and  then 
precipitate  with  hydrogen  sulphide  (§  119,  3). 

c.  COPPER  FROM  MERCURICUM  AND  CADMIUM. 

Mix  the  solution,  as  in  J,  with  potassium  cyanide  until  the  112 
precipitate  which  is  first  thrown  down  redissolves ;  add  some 
more  potassium  cyanide,  then  hydrogen  sulphide  water  or 
ammonium  sulphide,  as  long  as  a  precipitate  forms.  The 
cadmium  and  mercury  sulphides  are  completely  thrown  down, 
whilst  the  copper  remains  in  solution,  as  sulphide  dissolved  in 
potassium  cyanide.  Allow  the  precipitate  to  subside,  decant 
repeatedly,  treat  the  precipitate,  for  security,  once  more  with 
solution  of  potassium  cyanide,  heat  gently,  filter,  and  wash 
the  sulphides  of  the  metals.  To  determine  the  copper  in  the 
filtrate,  evaporate  the  latter,  with  addition  of  nitric  and  sul- 
puric  acids,  until  there  is  no  longer  any  odor  of  hydrocyanic 
acid,  and  then  precipitate  with  hydrogen  sulphide  (§  119,  3). 

d.  ALL  THE  METALS  OF  THE  FIFTH   GROUP  FROM  EACH 

OTHER. 

Mix  the  dilute  solution  with  sodium  carbonate,  then  with  113 
potassium  cyanide  in  excess,  digest  some  time  at  a  gentle  heat, 
and  filter.  On  the  filter  you  have  lead  carbonate  and  bismuth 
carbonate  (containing-  alkali) ;  separate  the  two  metals  by  a 
suitable  method.  ,  Add  to  the  Citrate  dilute  nitric  acid  in 
excess,  warm  gently  till  the  cuprous  sulphocyanate  first  pre- 
cipitated with  the  silver  cyanide  has  redissolved,  and  filter 
off  the  undissolved  silver  salt,  which  is  to  be  determined  as 
directed  §  115,  3.  Neutralize  the  filtrate  with  sodium  car- 
bonate, add  potassium  cyanide,  and  pass  hydrogen  sulphide  in 
excess.  Add  now  some  more  potassium  cyanide,  to  redissolve 
the  copper  sulphide  wrhich  may  have  fallen  down,  and  filter 
the  fluid,  which  contains  the  whole  of  the  copper,  from  the 
precipitated  sulphides  of  mercury  and  cadmium.  Determine 
the  copper  as  directed  in  c,  and  separate  the  mercury  and  cad- 
mium as  in  108. 


§  163.]  BASES   OF   GROUP  V.  549 

4.  Methods  based  on  the  Formation  and  Separation 
of  insoluble  Basic  Salts. 

a.  BISMUTH  FROM  COPPER,  CADMIUM,  AND  MERCURICUM  (also 
from  the  basic  radicals  of  the  first  four  groups,  with  the  excep- 
tion of  ferric  iron). 

Precipitate  the  bismuth  as  basic  chloride  according  to  §  120,  114 
4,  and  throw  down  the  copper,  &c.,  in  the  filtrate  by  hydro- 
gen sulphide.     Results  thoroughly  satisfactory  (H.  ROSE*). 

b.  BISMUTH  FROM  LEAD  AND  CADMIUM. 

Separate  the  bismuth  according  to  §  120,  1,  c,  as  basic  115 
nitrate,  and  precipitate  the  lead  and  cadmium  in  the  filtrate 
by  hydrogen  sulphide.     Results  very  satisfactory  (J.  Lowsf). 

c.  BISMUTH  AND  COPPER  FROM  LEAD  AND  CADMIUM. 
Separate  the  bismuth  after  §  120, 1,  c1,  as  basic  nitrate,  then 

heat  the  dish  on  the  water-bath  till  the  normal  copper  nitrate 
is  completely  converted  into  bluish-green  basic  salt  and  no 
blue  solution  is  produced  on  addition  of  water.  Allow  to  cool, 
treat  with  an  aqueous  solution  of  ammonium  nitrate  (1  in  500), 
filter,  wash  with  the  same  solution,  and  separate  in  the  solution 
lead  from  cadmium;  in  the  residue  copper  from  bismuth. 
Results  very  satisfactory  (J.  LOWE,  loc.  cit.). 

5.  Method  based  upon  the  Precipitation  of  some  of 
the  Metals  l>y  Ammonia  or  Ammonium  Carbonate. 

COPPER  FROM  BISMUTH. 

Mix  the  (nitric  acid)  solution  with  ammonium  carbonate  116 
in  excess,  and  warm  gently.  The  bismuth  separates  as  car- 
bonate, whilst  the  copper  carbonate  is  redissolved  by  the  excess 
of  ammonium^  carbonate.  As  the  precipitate,  however,  gen- 
erally retains  a  little  copper,  it  is  necessary  to  redissolve  it, 
after  washing,  in  nitric  acid,  and  precipitate  again  with  ammo- 
nium carbonate ;  the  same  operation  must  be  repeated  a  third 
time  if  required.  Some  solution  of  ammonium  carbonate  may 
be  added  to  the  water  used  for  washing.  Apply  heat  to  the 
filtrate  that  the  ammonium  carbonate  may  volatilize,  acidify 
cautiously  with  hydrochloric  acid,  and  determine  the  copper 
as  cuprous  sulphide  (§  119,  3).  The  oxide  of  bismuth  thus 

*  Pogg.  Aniial.  110,  430.  f  Journ.  f.  prakt.  Chem.  74,  345. 


550  SEPARATION.  [§  163. 

obtained  is  quite  copper-free,  but  a  little  bismuth  passes  into 
the  copper  solution,  hence  the  separation  does  not  give  such 
exact  results  as  that  in  114  (H.  ROSE*). 

6.  Method  based  on  the  Precipitation  of  the  Copper 
as  Cuprous  Sulphocyanate. 

COPPER  FROM  CADMIUM  (and  the  metals  of  Groups  I.  —  IY., 
comp.  101).     . 

Precipitate  the  copper  according  to  §  119,  3,  Z>,  as  cuprous  117 
sulphocyanate  (RIVOT),  and  the  cadmium  from  the  filtrate  as 
sulphide.     Results  good  (H.  ROSE).     Palladium  may  also  be 
separated  from  copper  in  this  way 


Y.  Method  based  upon  the  different  deportment  of 
the  Chromates. 

BISMUTH  FROM  CADMIUM. 

Precipitate  the  bismuth  as  directed  §  120,  2.     The  filtrate  118 
contains  the  whole  of  the  cadmium.     Concentrate  by  evapora- 
tion, and  then  precipitate  the  cadmium  by  the  cautious  addi- 
tion of  sodium  carbonate,  as  directed  §  121,  1,  a  (J.  LowE,J 
"W.  PEARSON§).     The  results  given  are  satisfactory. 

8.  Method  based  upon  the  different  deportment  of 
the  Sulphides  with  Acids. 

a.  MERCURICUM  FROM  SILVER,  BISMUTH,  COPPER,  CADMIUM, 
AND  (but  less  well)  FROM  LEAD. 

Boil  the  thoroughly  washed  precipitated  sulphides  with  119 
perfectly  pure  moderately  dilute  nitric  acid.  The  mercuric 
sulphide  is  left  undissolved,  the  other  sulphides  are  dissolved. 
No  chlorine  may  be  present,  and  it  is  necessary  that  the  mer- 
curic sulphide  should  be  pure,  that  is,  free  from  finely  divided 
mercury,  which,  as  is  well  known,  is  precipitated  when  mer- 
curous  salts  are  treated  with  hydrogen  sulphide.  G.  v.  RATH|| 
employed  this  method,  which  is  so  universally  used  in  qualita- 
tive analysis;  with  perfect  success  for  the  separation  of  mer- 
cury from  bismuth. 

*  Pogg.  Annal.  110,  430. 

f  Annal.  d.  Chem.  u.  Pharm.  140,  144;  Zeitschr.  f.  anal.  Chem.  5,  403. 
t  Journ.  f.  prakt.  Chem.  67,  439.  |  Pogg.  Anual.  96,  322. 

§  Phil.  Mag.  11,  204. 


§163.]  BASES    OF   GKOUP   V.  551 

b.  COPPER  FROM  CADMIUM. 

Boil  the   well- washed  precipitate  of  the  sulphides  with  120 
dilute  sulphuric  acid  (1  part  concentrated  acid  and  5  parts 
water),  and,  after  some  time,  filter  the  undissolved  copper  sul- 
phide, to  be  determined  according  to  §  119,  3,  from  the  solu- 
tion containing  the  whole  of  the  cadmium  (A.  "W.  HOFMANN*). 

9.  Methods  based  upon  the  Volatility  of  some  of  the 
Metals,  Oxides,  Chlorides,  or  Sulphides  at  a  high  Tem- 
perature. 

a.  MERCURY  FROM  SILVER,  LEAD,  COPPER  (in  general  from 
the  metals  forming  non- volatile  chlorides). 

Precipitate  with  hydrogen  sulphide,  collect  the  precipi-  121 
tated  sulphides  on  a  weighed  filter,  dry  at  100°,  weigh,  and 
mix  uniformly.     Introduce  an  aliquot  part  into  the  bulb  d, 


FIG.  70. 

(fig.  TO),  pass  a  slow  stream  of  chlorine  gas,  and  apply  a  gen- 
tle heat  to  the  bulb,  increasing  this  gradually  to  faint  redness. 
To  ensure  complete  absorption  it  is  well  to  have  another  small 
U-tube  connected  with  e.  The  excess  of  chlorine  escaping 
from  the  latter  during  the  operation  may  be  conducted  into  a 
flue  or  into  a  carboy  containing  moist  slaked  lime.  First  sul- 
phur chloride  distils  over,  which  decomposes  with  the  water 
in  e  (p.  463) ;  then  the  mercuric  chloride  formed  volatilizes, 
condensing  partly  in  e,  partly  in  the  hind  part  of  d.  Cut  off 

*  Annal.  d.  Chem.  u.  Pharm.  115,  286. 


552  SEPARATION.  [§  163. 

that  part  of  the  tube,  rinse  the  sublimate  with  water  into  £, 
and  mix  the  contents  of  the  latter  with  the  water  in  the  second 
U-tube  (not  shown  by  the  figure).  Mix  the  solution  with 
excess  of  ammonia,  warm  gently  till  no  more  nitrogen  is 
evolved,  acidify  with  hydrochloric  acid,  and  then  determine 
in  the  fluid  filtered  from  the  sulphur,  which  may  still  remain 
undissolved,  the  mercury  as  directed  §  118,  3.  If  the  residue 
consists  of  silver  chloride  alone,  or  lead  chloride  alone,  you 
may'  weigh  it  at  once ;  but  if  it  contains  several  metals,  you 
must  reduce  the  chlorides  by  ignition  in  a  stream  of  hydrogen, 
and  dissolve  the  reduce^  metals  in  nitric  acid,  for  their  ulte- 
rior separation.  Bear  in  mind  that,  in  presence  of  lead,  the 
sulphides  and  the  chlorides  must  be  heated  gently  ^  in  the  chlo- 
rine and  hydrogen  respectively,  otherwise  some  lead  chloride 
might  volatilize. 

In  alloys  or  mixtures  of  oxides  the  mercury  may  usually 
be  determined  with  simplicity  from  the 'loss  on  ignition  in  the 
air  or  in  hydrogen. 

b.  BISMUTH  FROM  SILVER,  LEAD,  AND  COPPER. 

The  separation  is  effected  exactly  in  the  same  way  as  that  122 
of  mercury  from  the  same  metals  (121).  The  method  is  more 
especially  convenient  for  the  separation  of  the  metals  in 
alloys.  Care  must  be  taken  not  to  heat  too  strongly,  as  other- 
wise lead  chloride  might  volatilize ;  nor  to  discontinue  the 
application  of  heat  too  soon,  as  otherwise  bismuth  would 
remain  in  the  residue.  AUG.  VOGEL  *  gives  360°  to  370°  as 
the  best  temperature.  Put  water  containing  hydrochloric  acid 
in  U-tubes,  which  serve  as  receivers  (fig.  70),  and  determine 
the  bismuth  therein  according  to  §  120. 

10.   Precipitation  of  one  Meted  in  the  Metallic  State 
lyy  another  or  the  lower  Oxide  of  another, 
a.  LEAD  FROM  BISMUTH. 

Precipitate  the  solution  with  ammonium  carbonate  (§  116,  123 
1,  a  and  §  120,  1,  a\  wash  the  precipitated  carbonates,  and 
dissolve  in  acetic  acid,  in  a  flask ;  place  a  weighed  rod  of  pure 
lead  in  the  solution,  and  nearly  fill  up  with  water,  so  that  the 


*  Zeitscbr.  f.  anal.  Chem.  13,  61. 


§  163.]  BASES   OF  GROUP   V.  553 

rod  may  be  entirely  covered  by  the  fluid ;  close  the  flask,  and 
let  it  stand  for  about  12  hours,  with  occasional  shaking. 
Wash  the  precipitated  bismuth  off  from  the  lead  rod,  collect 
on  a  filter,  wash,  and  dissolve  in  nitric  acid  ;  evaporate  the 
solution,  and  determine  the  bismuth  as  directed  §  120.  Deter- 
mine the  lead  in  the  filtrate  as  directed  §  116.  Dry  the 
leaden  rod,  and  weigh ;  subtract  the  loss  of  weight  which  the 
rod  has  suffered  in  the  process  from  the  amount  of  the  lead 
obtained  from  the  filtrate  (ULLGRE'N  *).  PATERA  f  recom- 
mends precipitating  from  dilute  nitric  solution,  washing  the 
precipitated  bismuth  first  with  water,  then  with  alcohol,  trans- 
ferring to  a  small  filter,  drying  and  weighing.  If  it  is  feared 
that  the  finely  divided  bismuth  has  undergone  oxidation,  it  is 
well  to  fuse  it  with  potassium  cyanide  (§  120,  4). 

11.  Separation  of  Silver  by  Cupellation. 
CUPELLATION  was  formerly  the  universal  method  of  deter-  124 

mining  SILVER  in  alloys  with  COPPER,  LEAD,  etc.  The  alloy  is 
fused  with  a  sufficient  quantity  of  pure  lead  to  give  to  1  part 
of  silver  16  to  20  parts  of  lead,  and  the  fused  mass  is  heated, 
in  a  muffle,  in  a  small  cupel  made  of  compressed  bone-ash. 
Lead  and  copper  are  oxidized,  and  the  oxides  absorbed  by  the 
cupel,  the  silver  being  left  behind  in  a  state  of  purity.  One 
part  by  weight  of  the  cupel  absorbs  the  oxide  of  about  2  parts 
of  lead ;  the  quantity  of  the  sample  to  be  used  in  the  experi- 
ment may  be  estimated  accordingly.  This  method  is  only 
rarely  employed  in  laboratories  ;  :£  I  have  given  it  a  place  here, 
however,  because  it  is  one  of  the  safest  processes  to  deter- 
mine very  small  quantities  of  silver  in  alloys.  § 

12.  Methods  depending  on  the  Volumetric  Estima- 
tion of  one  Metal. 

a.  COPPER  OF  CUPROUS  COMPOUNDS  IN  PRESENCE  OF  CUPRIC 
COMPOUNDS.] 

Dissolve  the  substance,  if  necessary  in  a  current  of  carbonic  125 

*  BERZELIUS'  Jahresber.  31,  148.  f  Zeitschr.  f.  anal.  Chem.  5,  226. 

$  For  details  of  this  process  consult  "Bodemann  and  Kerl's  Assaying," 
translated  by  GOODYEAR  ;  or  "Notes  on  Assaying,"  by  P.  DE  RICKETTS. 

§  Compare  MALAGUTI  and  DUROCHER,  Comp.  rend.  29,  689;  DINGLER,  115, 
376.  Also  W.  HAMPE,  Zeitschr.  f.  anal.  Chem.  11,  221. 

|  The  method  of  COMMAILLE  (Comp.  rend.  56,  309)  can  no  longer  be  relied 


554  SEPARATION.  [§  164, 

acid,  in  hydrochloric  acid,  and  add  ferric  chloride.  A  volu- 
metric determination  of  the  amount  of  iron  reduced  to  fer- 
rous salt  affords  a  basis  for  calculating  the  amount  of  copper 
present  originally  as  a  cuprous  compound.  Or  if  a  known 
quantity  of  ferric  chloride  is  used,  a  determination  of  the  iron 
remaining  in  the  state  of  a  ferric  salt  suffices  equally  well. 

It.    SILVER    IN    PRESENCE   OF    LEAD   AND    C/OPPER. 

Small  quantities  of  silver  may  be  estimated  by  PISANI'S 
method,  §  115,  II. 


Sixth  Group. 

GOLD PLATINUM TIN ANTIMONY — (ANTIMONIC   ACID) — ARSENIOUS 

ACID AKSENIC   ACID. 

I.  SEPARATION  OF  THE  METALS  OF  THE  SIXTH  GROUP  FROM  THOSE 

O1?    THE    FIRST    FlVE    GROUPS. 

§  164. 
INDEX.     (The  numbers  refer  to  those  in  the  margin.) 

-     Gold  from  the  metals  of  Groups  I.— III.,  126,  131. 
Group  IV.,  126,  129,  131. 
silver,  129,  147. 
mercury,  129,  142. 
lead,  129,  152. 
copper,  129,  131. 
"         bismuth,  129,  131,  152. 
"         cadmium,  129,  131. 
Platinum  from  the  metals  of  Groups  I. — III.,  126,  132. 

Group  IV.,  126,  130,  132. 
silver,  130,  147. 
mercury,  130,  142. 
lead,  130. 

•"  copper,  130,  132. 

bismuth,  130,  132. 
cadmium,  130,  132. 

Tin  from  the  metals  of  Groups  I.  and  II.,  126,  135,  141. 
Group  III.,  126,  135. 


upon,  since  STAS  has  shown  that  the  finely  divided  silver  thrown  down  by 
ammoniacal  solution  of  cuprous  chloride  dissolves  largely  in  ammonia  with 
access  of  air. 


§  164.]  METALS   OF   GROUP  VI.  555 

Tin  from  zinc,  126,  128,  133,  135. 

manganese,  126,  128,  135. 
nickel  and  cobalt,  126,  128,  133,  135,  140. 
iron,  126,  128. 
silver,  127,  128,  133,  140. 
mercury,  127,  128,  133. 
lead,  127,  128,  133,  140. 
copper,  127,  128,  133,  135,  180. 
bismuth,  127,  128. 
cadmium,  127,  128,  133,  135. 
Antimony  from  the  metals  of  Groups  I.  and  II.,  126. 

Group  III.,  126. 
zinc,  126,  128,  134. 
manganese,  126,  128. 
nickel  and  cobalt,  126,  128,  134,  139,  140. 
iron,  126,  128,  138. 
silver,  127,  128,  134,  140. 
mercury,  127,  128,  134,  136,  148. 
lead,  127,  128,  134,  140,  150. 
copper,  127,  128,  134,  138,  140,  151. 
bismuth,  127,  128. 
cadmium,  127,  128,  134. 
Arsenic  from  the  metals  of  Group  I.,  126,  145,  146. 

"    .  "  II.,  126,  137,  145,  146. 

III.,  126,  144,  145. 
zinc,  126,  128,  137,  143,  145,  146. 
manganese,  126,  128,  137,  143,  144,  145,  146. 
nickel  and  cobalt,  126,  128,  137,  139,  140,  143,  144,  145,  146. 
iron,  126,  128,  137,  138,  143,  144,  145. 
silver,  127,  128,  137,  140,  145. 
mercury,  127,  128,  145,  148. 
lead,  127,  128,  137,  140,  145,  149. 
copper,  127,  128,  137,  138,  140,  143,  144,  145,  151. 
bismuth,  127,  128,  137,  145. 
cadmium,  127,  128,  137,  144,  145. 

A.   General  Methods. 

1.  Method  based  upon  the  Precipitation  of  Metals 
of  the  Sixth  Group  from  Acid  Solutions  by  Sulphuretted 
Hydrogen. 

ALL  METALS  OF  THE  SIXTH  GROUP  FROM   THOSE   OF  THE 
FIRST  FOUR  GROUPS. 

Conduct  into  the  acid*   solution   hydrogen  sulphide  in  126 
excess,  and  filter  off  the  precipitated  sulphides  (corresponding 
to  the  oxides  of  the  sixth  group). 


*  Hydrochloric  acid  answers  best  as  acidifying  agent. 


556  SEPARATION.  [§  164. 

The  points  mentioned  96,  <*,  /?,  and  7,  must  also  be 
attended  to  here.  As  regards  7,  antimony  and  tin  are  to  be 
inserted  between  cadmium  and  mercury,  in  the  order  of 
metals  there  given.  With  respect  to  the  particular  conditions 
required  to  secure  the  proper  precipitation  of  certain  metals 
of  the  sixth  group,  I  refer  to  Section  IY.  I  have  to  remark 
in  addition : 

a.  That  hydrogen  sulphide  fails  to  separate  arsenic  acid 
from  zinc,  as,  even  in  presence  of  a  large  excess  of  acid, 
the  whole  or  at  least  a  portion  of  the  zinc  precipitates  with 
the  arsenic  (WOHLER).  To  secure  the  separation  of  the  two 
bodies  in  a  solution,  the  arsenic  acid  must  first  be  converted 
into  arsenious  acid,  by  heating  with  sulphurous  acid,  before 
the  hydrogen  sulphide  is  conducted  into  the  fluid. 

ft.  That  in  presence  of  antimony,  tartaric  acid  should  be 
added,  as  otherwise  the  sulphide  of  antimony  will  contain 
chloride  ;  and  that  sulphide  of  antimony,  when  thrown  down 
from  a  boiling  solution  by  hydrogen  sulphide,  becomes  black 
after  a  time,  and  so  dense  that  it  is  deposited  like  sand, 
whereby  the  filtration  and  washing  are  much  facilitated  (S.  P. 

SCHAFELER  *). 

2.  Method  based  upon  the  Solubility  of  the  Sulphides 
of  the  JHetals  of  the  Sixth  Group  in  Sulphides  of  ilie 
Alkali  Metals. 

a.  THE  METALS  OF  GROUP  VI.  (with  the  exception  of  Gold 
and  Platinum)  FROM  THOSE  OF  GROUP  V. 

Precipitate  the  acid  solution  with  hydrogen  sulphide,  pay-  127 
ing  due  attention  to  the  directions  given  in  Section  IV.  under 
the  heads  of  the  several  metals,  and  also  to  the  remarks  in 
126.  The  precipitate  consists  of  the  sulphides  of  the  metals 
of  Groups  V.  and  VI.  Wash,  and  treat  at  once  with  yellow 
ammonium  sulphide  in  excess.  (It  is  usually  best  to  spread 
out  the  filter  in  a  porcelain  dish,  add  the  ammonium  sulphide, 
cover  with  a  large  watch-glass,  and  place  on  a  heated  water- 
bath.  Unnecessary  exposure  to  air  should  be  avoided.)  Add 
some  water,  filter  off  the  clear  fluid,  treat  the  residue  again 


*  Berichte  der  deutschen  chem.  Gesellsch.  1871,  279.     I  have  myself  con 
firmed  these  observations. 


§  164.]  METALS   OF   GROUP  VI.  557 

with  ammonium  sulphide,  digest  a  short  time,  repeat  the  same 
operation,  if  necessary,  a  third  and  fourth  time,  filter,  and 
wash  the  residuary  sulphides  of  Group  V .  with  water  contain- 
ing ammonium  sulphide.  If  stannous  sulphide  is  present, 
some  flowers  of  sulphur  must  be  added  to  the  ammonium  sul- 
phide, unless  the  latter  be  very  yellow.  In  presence  of  copper, 
the  sulphide  of  which  is  a  little  soluble  in  ammonium  sulphide, 
sodium  sulphide  should  be  used  instead.  However,  this  sub- 
stitution can  be  made  only  in  the  absence  of  mercury,  since 
the  sulphide  of  that  metal  is  soluble  in  sodium  sulphide. 

Add  to  the  alkaline  filtrate,  gradually,  hydrochloric  acid  in 
small  portions,  until  the  acid  predominates ;  allow  to  subside, 
and  then  filter  off  the  sulphides  of  the  metals  of  the  sixth 
group,  which  are  mixed  with  sulphur. 

If  a  solution  contains  much  arsenic  acid  in  presence  of 
small  quantities  of  copper,  bismuth,  &c.,  it  is  convenient  to 
precipitate  these  metals  (together  with  a  very  small  amount  of 
arsenious  sulphide)  by  a  brief  treatment  with  hydrogen  sul- 
phide. Filter,  extract  the  precipitate  with  ammonium  sulphide 
(or  potassium  sulphide),  acidify  the  solution  obtained,  mix  it 
with  the  former  filtrate  containing  the  principal  quantity  of 
the  arsenic,  and  proceed  to  treat  further  with  hydrogen  sul- 
phide  (§  127,  4,  I). 

b.  THE  METALS  OF  GROUP  VI.  (with  the  exception  of  Gold 
and  Platinum)  FROM  THOSE  OF  GROUPS  IV.  AND  V. 

a.  Neutralize  the  solution  with  ammonia,  add  ammonium  128 
chloride,  if  necessary,  and  then  yellow  ammonium  sulphide  in 
excess ;  digest  in  a  closed  flask,  for  some  time  at  a  moderate 
heat;  and  then  proceed  as  in  127.  Repeated  digestion  with 
fresh  quantities  of  ammonium  sulphide  is  indispensable.  On 
the  filter,  you  have  the  sulphides  of  the  metals  of  Groups  IV 
and  V.  Wash  with  water  containing  ammonium  sulphide. 
In  presence  of  nickel,  this  method  offers  peculiar  difficul- 
ties ;  traces  of  mercuric  sulphide,  too,  are  liable  to  pass  into 
the  filtrate.  In  presence  of  copper  (and  absence  of  mer- 
cury), soda  and  sodium  sulphide  are  substituted  for  ammonia 
and  ammonium  sulphide.* 

*  The  accuracy  of  this  method  has  been  called  in  question  by  BLOXAM  (Quart. 
Journ.  Chem.  Soc.  5,  119).     That  chemist  found  that  ammonium  sulphide  fails 


558  SEPARATION.  [§  164. 

/3.  In  the  analysis  of  solid  compounds  (oxides  or  salts),  it 
is  in  most  cases  preferable  to  fuse  the  substance  with  3  parts 
of  dry  sodium  carbonate  and  3  of  sulphur,  in  a  covered  porce- 
lain crucible.  When  the  contents  are  completely  fused,  arid 
the  excess  of  sulphur  is  volatilized,  the  mass  is  allowed  to  cool, 
and  then  treated  with  water,  which  dissolves  the  sulphosalts 
of  the  metals  of  the  sixth  group,  leaving  the  sulphides  of 
Groups  IY.  and  Y.  undissolved.  By  this  means,  even  ignited 
stannic  oxide  may  be  readily  tested  for  iron,  &c.,  and  the 
amount  of  the  admixture  determined  (H.  ROSE).  The  solu- 
tion of  the  sulphosalts  is  treated  as  in  127.  In  the  presence 
of  copper,  traces  of  the  sulphide  may  be  dissolved  with  the 
sulphides  of  Group  YI.  Occasionally  a  little  ferrous  sulphide 
dissolves,  coloring  the  solution  green.  In  that  case  add  some 
ammonium  chloride,  and  digest  till  the  solution  has  turned 
yellow.  Instead  of  the  mixture  of  sodium  carbonate  and  sul- 
phur you  may  also  use  already  prepared  hepar  sulphuris,  or, 
as  FROHDE*  says,  you  may  fuse  the  substance  with  4  or  5  parts 
of  sodium  thiosulphate. 

B.  Special  Methods. 

1.  Methods  based  upon  the  Insolubility  of  some 
Metals  of  the  Sixth  Group  in  Acids. 

a.  GOLD  FROM  METALS  OF  GROUPS  IY.  AND  Y.  IN  ALLOYS. 

a.  Boil  the  alloy  with  pure  nitric  acid  (not  too  concen-  129 
trated),  or,  according  to  circumstances,  with  hydrochloric  acid. 
The  other  metals  dissolve,  the  gold  is  left.  The  alloy  must 
be  reduced  to  filings,  or  rolled  out  into  a  thin  sheet.  If  the 
alloy  were  treated,  with  concentrated  nitric  acid,  and  at  a  tem- 
perature below  boiling,  a  little  gold  might  dissolve  in  conse- 
quence of  the  co-operation  of  nitrous  acid.  In  the  presence 
of  silver  and  lead,  this  method  is  only  applicable  when  they 


to  separate  small  quantities  of  stannic  sulphide  from  large  quantities  of  mercuric 
sulphide  or  cadmium  sulphide  (1  :  100);  and  that  more  especially  the  separation 
of  copper  from  tin  and  antimony  (also  from  arsenic)  by  this  method  is  a  failure, 
as  nearly  the  whole  of  the  tin  remains  with  the  copper.  The  latter  statement  I 
cannot  confirm,  for  Mr.  Lucius,  in  my  laboratory,  has  succeeded  in  separating 
copper  from  tin  by  means  of  yellowish  sodium  sulphide  completely;  but  it  is 
indispensable  to  digest  three  or  four  times  with  sufficiently  large  quantities  of 
the  solvent,  as  stated  in  the  text. 
*  Zeitschr.  f .  anal.  Chem.  5,  405. 


§  164.]  METALS   OF   GROUP   VI.  559 

amount  to  more  than  80  per  cent.,  since  otherwise  they  are 
not  completely  dissolved.  Alloys  of  silver  and  gold  contain- 
ing less  than  80  per  cent,  of  silver  are  therefore  fused  with  3 
parts  of  lead,  before  they  are  treated  with  nitric  acid.  The 
residuary  gold  is  weighed ;  but  its  purity  must  be  ascertained, 
by  dissolving  in  cold  dilute  nitrohydrochloric  acid,  not  in  con- 
centrated hot  acid,  as  silver  chloride  also  is  soluble  in  the  latter. 
In  the  presence  of  silver,  a  small  quantity  of  its  chloride  is 
usually  obtained  here.  If  it  can  be  weighed,  it  should  be 
reduced  and  deducted. 

At  the  Mint  Conference  held  at  Vienna  in  1857,  the  fol- 
lowing process  was  agreed  upon  for  the  mints  in  the  several 
states  of  Germany.  Add  to  1  part  of  gold,  supposed  to  be 
present,  2^  parts  of  pure  silver ;  wrap  both  the  alloy  and  the 
silver  in  a  paper  together,  and  introduce  into  a  cupel  in  which 
the  requisite  amount  of  lead  is  just  fusing.*  After  the  lead  . 
has  been  absorbed,f  the  button  is  flattened  by  hammering  or 
rolling,  then  ignited  and  rolled.  The  rolls  are  treated  first 
with  nitric  acid  of  1*2  sp.  gr.,  afterwards  with  nitric  acid  of 
1-3  sp.  gr.,  rinsed,  ignited,  and  weighed.^  Even  after  boiling 
again  with  nitric  acid  of  1*3  sp.  gr.,  they  retain  -75  to  *001 
of  silver  which  will  remain  as  chloride  if  the  rolls  are  treated 
with  cold  dilute  aqua  regia  (H.  ROSSLER,  loc.  cit.).  • 

ft.  Heat  the  alloy  (previously  filed  or  rolled)  in  a  capacious 
platinum  dish  with  a  mixture  of  2  parts  pure  concentrated 
sulphuric  acid  and  1  part  water,  until  the  evolution  of  gas  has 
ceased  and  the  sulphuric,  acid  begins  to  volatilize  ;  or  fuse  the 
alloy  with  potassium  disulphate  (H.  ROSE).  Separate  the  gold 
from  the  sulphates  of  the  other  metals,  by  treating  the  mass 
with  water  which  should  finally  be  boiling.  It  is  advisable  to 
repeat  the  operation  with  the  separated  gold,  and  ultimately 

*  If  the  weighed  sample,  say  '25  grm.,  contains  98-92£  gold,  3  grm.  of  lead 
are  required;  if  92-87'5,  4  grm. ;  if  87 '5-75,  5  grm. ;  if  75-60,  6  grm.;  if  60-35, 
7  grm. ;  if  less  than  35,  8  grm. 

f  A  small  quantity  of  gold — from  one  to  three  thousandths — is  always  lost 
in  cupellation.  The  loss  increases  with  the  amount  of  lead,  and  is  also  depen- 
dent on  the  proportion  of  silver  to  gold.  The  more  silver  present  the  less  is  the 
loss  of  gold.  In  large  buttons  the  loss  is  less  than  in  small  ones  (H.  ROSSLER, 
Ding,  polyt.  Journ.  206,  185;  Zeitschr.  f.  anal.  Chem.  13,  87). 

\  Kunst-und  Gewerbeblatt  f.  Baiern,  1857,  151;  Chem.  Centralbl.  1857,  307 
Polyt.  Centralbl.  1857,  1151,  1471,  1639. 


560  SEPARATION.  [§  164. 

test  the  purity  of  the  latter.     In  presence  of  lead  this  method 
is  not  good. 

y.  The  methods  given  in  a  and  /?  may  be  united,  i.e.,  the 
cupelled  and  thinly-rolled  rnetal  may  be  first  warmed  with 
nitric  acid  of  1'2  sp.  gr.,  then  thoroughly  washed,  the  gold 
boiled  5  minutes  with  concentrated  sulphuric  acid,  washed 
again,  and  ignited  (MASCAZZINI,  BUGATTI). 

#.  PLATINUM   FKOM   METALS   OF    GROUPS   IY.   AND  Y.  IN 
ALLOYS. 

The  separation  is  effected  by  heating  the  alloy  in  filings  130 
or  foil  with  pure  concentrated  sulphuric  acid,  with  addition  of 
a  little  water,  or  by  fusing  with  potassium  disulphate  (129,  ft) ; 
but  not  with  nitric  acid,  as  platinum  in  alloys  will,  under  cer- 
tain circumstances,  dissolve  in  that  acid. 

2.  Method  based  upon  the  Separation  of  Gold  in 
the  metallic  state. 

GOLD  FKOM  ALL  METALS  OF  GROUPS  I. — Y.,  with  the  excep- 
tion of  LEAD,  MERCURY,  AND  SILVER. 

Precipitate  the  hydrochloric  acid  solution  with  oxalic  acid  131 
as  directed  §  123  5,  y^  or  with  ferrous  sulphate,  §  123,  J,  <*, 
and  filter  off  the  gold  when  it  has  completely  separated.  Take 
care  to  add  a  sufficient  quantity  of  hydrochloric  acid  after  the 
reduction  to  insure  solution  of  any  oxalates.  In  the  presence 
of  copper  the  addition  of  hydrochloric  acid  does  not  suffice, 
since  the  coprecipitated  cupric  oxalate  will  dissolve  with  diffi- 
culty in  this  acid.  E.  PURGOTTI*  recommends  in  this  case, 
after  precipitation,  adding  potash  cautiously  to  the  boiling  hot 
fluid  till  it  is  neutral,  and  then  if  necessary  some  normal 
potassium  oxalate.  Double  oxalate  of  copper  and  potash  will 
be  formed  which  dissolves  with  a  blue  color.  The  gold  after 
washing  will  now  be  pure. 

3.  Method  based  upon  the   Precipitation  of  Pla- 
tinum as  Potassium  Platinic,  or  Ammonium  Platinic 
Chloride. 

PLATINUM  FROM  THE  METALS  OF  GROUPS  IY.  AND  Y., 
with  the  exception  of  MERCURY  IN  MERCUROUS  COMPOUNDS, 
LEAD,  AND  SILVER. 

Precipitate    the    platinum    with    potassium    chloride    or  132 

*  Zeitschr.  f .  anal.  Chem.  9,  128. 


§  164.]  METALS    OF   GROUP   VI.  561 

ammonium  chloride  as  directed  §  124,  and  wash  the  precipi- 
tate thoroughly  with  alcohol.  The  platinum  prepared  from 
the  precipitated  ammonium  or  potassium  salt  is  to  be  tested 
after  being  weighed,  to  see  whether  it  yields  any  metal 
(especially  iron)  to  fusing  potassium  disulphate. 

4.  Methods  based  upon  the  Separation  of  Oxides 
insoluble  in  Nitric  Add. 

a.  TIN  FROM  METALS  OF  GROUPS  IY.  AND  Y.  (not  from 
Bismuth,  Iron,  or  Manganese*)  IN  ALLOYS. 

Treat  the  finely  divided  alloy,  or  the  metallic  powder  133 
obtained  by  reducing  the  oxides  in  a  stream  of  hydrogen  with 
nitric  acid,  as  directed  §  126,  1,  a.  The  filtrate  contains  the 
other  metals  as  nitrates.  As  stannic  oxide  is  liable  to  retain 
traces  of  copper  and  lead  and  iron,  you  must,  in  an  accurate 
analysis,  test  an  aliquot  part  of  it  for  these  bodies,  and  determine 
their  amount  as  directed  128,  ft. 

BRUNNER  recommends  the  following  course  of  proceeding, 
by  which  the  presence  of  copper  in  the  tin  may  be  effectually 
guarded  against.  Dissolve  the  alloy  in  a  mixture  of  1  part  of 
nitric  acid,  4  parts  of  hydrochloric  acid,  and  5  parts  of  water ; 
dilute  the  solution  largely  with  water,  and  heat  gently.  Add 
crystals  of  sodium  carbonate  until  a  distinct  precipitate  has 
formed,  and  boil.  (In  presence  of  copper,  the  precipitate 
must,  in  this  operation,  change  from  its  original  bluish-green 
to  a  brown  or  black  tint.)  When  the  fluid  has  been  in  ebulli- 
tion some  10  or  15  minutes,  allow  it  to  cool,  and  then  add 
nitric  acid,  drop  by  drop,  until  the  reaction  is  distinctly  acid ; 
digest  xhe  precipitate  for  several  hours,  when  it  should  have 
acquired  a  pure  white  color.  The  stannic  oxide  thus  obtained 
is  free  from  copper  ;  but  it  may  contain  some  iron,  which  can 
be  removed  as  directed  in  128,  ft. 

Before  the  stannic  oxide  can  be  considered  pure,  it  must 
be  tested  also  for  silicic  acid,  as  it  frequently  contains  traces  of 
this  substance.  To  this  end,  an  aliquot  part'  is  fused  in  plati- 


*  If  the  alloy  of  tin  contains  bismuth  or  manganese,  there  remains  with  the 
stannic  oxide,  bismuth  trioxide  or  manganese  sesquioxide,  which  cannot  be 
extracted  by  nitric  acid;  if  it  contains  iron,  on  the  contrary,  some  stannic  oxide 
always  dissolves  with  the  iron,  and  cannot  be  separated  even  by  repeated  evapo- 
ration (H.  ROSE,  Pogg.  Annal.  112,  169,  170,  172). 


562  SEPARATION.  [§  164. 

mim  with  3 — 4  parts  of  sodium  and  potassium  carbonate,  the 
fused  mass  boiled  with  water,  and  the  solution  filtered  ;  hydro- 
chloric acid  is  then  added  to  the  filtrate,  and,  should  silicic  acid 
separate,  the  fluid  is  filtered  off  from  this  substance.  The  tin  ' 
is  then  precipitated  by  hydrogen  sulphide,  and  the  silicic  acid 
still  remaining  in  the  filtrate  is  determined  in  the  usual  way 
(§  140).  If  hydrochloric  acid  has  produced  a  precipitate  of 
silicic  acid,  the  last  filtration  is  effected  on  the  same  filter 
(KHITTEL*). 

b.  ANTIMONY  FROM  THE  METALS  OF  GROUPS  IV.  AND  Y.  IN 
ALLOYS  (not  from  Bismuth,  Iron  and  Manganese). 

Proceed  as  in  133,  filter  off  the  precipitate,  and  convert  it  134 
by  ignition  into  antimony  tetroxide  according  to  §  125,  2. 
Results  only  approximate,  as  a  little  antimony  dissolves. 
Alloys  of  antimony  and  lead,  containing  the  former  metal  in 
excess,  should  be  previously  fused  with  a  weighed  quantity  of 
pure  lead  (VARRENTRAppf). 

5.  Methods  based  on  the  Precipitation  of  Tin  in 
Stannic  Salts  by  Normal  Salts  (e.g.,  Sodium  Sulphate) 
or  by  Sulphuric  Acid. 

TIN  FROM  THE  METALS  OF  GROUPS  I.,  II.,  Ill, ;  ALSO  FROM 
MANGANESE,  ZINC,  NICKEL  AND  COBALT,  COPPER,  CADMIUM 
(GOLD). 

Precipitate  the  hydrochloric  acid  solution,  which  must  135 
contain  the  tin  entirely  as  stannic  chloride,  according  to  §  126, 
1,  b,  by  ammonium  nitrate  or  sodium  sulphate  (LOWENTHAL), 
or  by  sulphuric  acid,  which,  H.  ROSE  says,  answers  equally 
well.  Alloys  are  always  treated  as  follows  :  First,  oxidize  by 
digestion  with  nitric  acid ;  when  no  more  action  takes  placer 
evaporate  the  greater  portion  of  the  .nitric  acid  in  a  porcelain 
dish,  moisten  the  mass  with  strong  hydrochloric  acid,  and  after 
half  an  hour  add  water,  in  which  the  metastannic  chloride  and 
the  other  chlorides  dissolve.  Alloys  of  tin  and  gold  are  dis- 
solved in  aqua  regia,  the  excess  of  acid  evaporated,  and  the 
solution  diluted  with  much  water,  before  precipitating  with 
sulphuric  acid. 

It  must  be  remembered  that  in  this  process  any  phosphoric 

*  Chem.  Centralbl.  1857,  929.  f  Dingler's  polyt.  Journ.  158,  316. 


§164.]  MKTALS    OF    GROUP   VI.  563 

acid  that  may  be  present  is  precipitated  entirely  or  partially 
with  the  tin.  After  the  precipitate  has  been  well  washed  by 
decantation,  LOWENTHAL  recommends  to  boil  with  a  mixture 
of  1  part  nitric  acid  (sp.  gr.  1/2)  and  9  parts  water,  then  to 
transfer  to  the  filter,  and  wash  thoroughly.  Results  very 
satisfactory.  If  the  fluid  contains  a  ferric  salt,  a  portion  of 
the  iron  always  falls  down  with  the  tin.  Hence  the  stannic 
oxide  must  be  tested  for  iron  according  to  128,  /?,  which,  if 
present,  must  be  determined  and  deducted. 

6.  Method   based  on,  the  Insolubility  of  Mercuric 
Sulphide  in  Hydrochloric  Acid. 

MERCURY  FROM  ANTIMONY. 

Digest  the  precipitated  sulphides  with  moderately  strong  136 
hydrochloric  acid  in  a  distilling  apparatus.  The  sulphide  of 
antimony  dissolves,  while  the  mercuric  sulphide  remains 
behind.  Expel  all  the  hydrogen  sulphide,  then  add  tartaric 
acid,  dilute,  filter,  mix  the  filtrate  with  the  distillate  which 
contains  a  little  antimony,  and  precipitate  with  hydrogen 
sulphide.  The  mercuric  sulphide  may  be  weighed  as  such  (F. 
FIELD*). 

7.  Methods  based  upon  the  Conversion  of  Arsenic 
and  Antimony  into  Alkali  Arsenate  and  Antimonate. 

a.  ARSENIC  FROM  THE  METALS  OF  GROUPS  II.,  IV.,  AND  Y. 

If  you  have  to  do  with  arsenites  or  arsenates,  fuse  with  3  137 
parts^of  sodium  and  potassium  carbonates  and  1  part  of  potas-* 
sium  nitrate ;  if  an  alloy  has  to  be  analyzed  it  is  fused  with  3 
parts  of  sodium  carbonate  and  3  parts  of  potassium  nitrate. 
In  either  case  the  residue  is  boiled  with  water,  and  the  solution, 
which  contains  the  arsenates  of  the  alkalies,  filtered  from  the 
undissolved  oxides  or  carbonates.  The  arsenic  acid  is  deter- 
mined in  the  filtrate  as  directed  §  127,  2.  If  the  quantity  of 
arsenic  is  only  small,  a  platinum  crucible  may  be  used,  other- 
wise a  porcelain  crucible  must  be  used,  as  platinum  would  be 
seriously  injured.  In  the  latter  case,  bear  in  mind  that  the 
fused  mass  is  contaminated  with  silicic  acid  and  alumina.  If 
the  alloy  contains  much  arsenic  a  small  quantity  may  be  readily 
lost  by  volatilization,  even  though  the  operation  be  cautiously 

*  Quart,  Journ.  Chein.  Soc.  12,  32. 


564  SEPARATION.  [§  164. 

conducted.  In  such  a  case,  therefore,  it  is  better  first  to  oxidize 
with  nitric  acid,  then  to  evaporate,  and  to  fuse  the  residue  as 
above  directed  with  sodium  carbonate  and  potassium  nitrate. 

b.  ARSENIC    AND    ANTIMONY    FROM    COPPER   AND    IRON, 
especially  in  ores  containing  sulphur. 

Diffuse  the  very  finely  pulverized  mineral  through  pure  138 
solution  of  potassa,  and  conduct  chlorine  into  the  fluid  (comp. 
p.  467).     The  iron  and  copper  separate  as  oxides,  the  solution 
contains   sulphate,   arsenate,    and    antirnonate   of    potassium 
(B-ivoT,  BEUDANT,  and  DAGUIN*). 

c.  ARSENIC  AND  ANTIMONY  FROM  COBALT  AND  NICKEL. 
Dilute  the  nitric  acid  solution,  add  a  large  excess  of  potassa,  139 

heat  gently,  and  conduct  chlorine  into  the  fluid  until  the  pre- 
cipitate is  black.  The  solution  contains  the  whole  of  the 
arsenic  and  antimony,  the  precipitate  the  nickel  and  cobalt  as 
sesquioxides  (RivoT,  BEUDANT,  and  DAGUIN,  loc.  cit.) 

8.  Methods  based  upon   the  Volatility  of  certain 
Chlorides  or  Metals. 

a.  TIN,  ANTIMONY,  ARSENIC  FROM  COPPER,  SILVER,  LEAD, 
COBALT,  NICKEL. 

Treat  the  sulphides  with  a  stream  of  perfectly  dry  chlorine,  140 
proceeding  exactly  as  directed  in  121.  In  presence  of  anti- 
mony, fill  the  receiver  e  (fig.  70)  with  a  solution  of  tartaric 
acid  in  water,  mixed  with  hydrochloric  acid.  The  metals  may 
be  also  separated  by  this  method  in  alloys.  The  alloy  must 
be  very  finely  divided.  Arsenical  alloys  are  only  very  slowly 
decomposed  in  this  way.  In  separating  arsenic  and  copper 
the  temperature  must  not  exceed  200°,  and  chlorine  water 
should  be  put  into  the  receiver  (PARNELLf).  If  tin  and  copper 
are  separated  in  this  manner,  according  to  the  experience  of 
H.  ROSE,:);  a  small  trace  of  tin  remains  with  the  copper  chloride. 

b.  STANNIC  OXIDE,  ANTIMONIOUS  OXIDE  (AND  ALSO 
ANTIMONIC  ACID),  ARSENIOUS  AND  ARSENIC  ACIDS,  FROM 
ALKALIES  AND  ALKALINE  EARTHS. 

Mix  the  solid  compound  with  5  parts  of  pure  ammonium  141 
chloride  in  powder,  in  a  porcelain  crucible,  cover  this  with  a 

*  Compt.  rend.  1853,  835;  Journ.  f.  prakt.  Chem.  61,  133. 
f  Chem.  News,  21,  133.  \  Pogg.  Annal.  112,  169. 


§  164.]  METALS   OF  GKOUP  VI.  565 

concave  platinum  lid,  on  which  some  ammonium  chloride  is ' 
sprinkled,  and  ignite  gently  until  all  ammonium  chloride  is 
driven  off ;  mix  the  contents  of  the  crucible  with  a  fresh  por- 
tion of  that  salt,  and  repeat  the  operation  until  the  weight 
remains  constant.  In  this  process,  the  chlorides  of  tin,  anti- 
mony, and  arsenic  escape,  leaving  the  chlorides  of  the  alkalies 
and  alkali-earth  metals.  The  decomposition  proceeds  most 
rapidly  with  alkali  salts.  With  regard  to  salts  of  alkali-earth 
metals  it  is  to  be  observed  that  those  which  contain  antimonic 
acid  or  stannic  oxide  are  generally  decomposed  completely  by 
a  double  ignition  writh  ammonium  chloride  (magnesium  alone 
cannot  be  separated  perfectly  from  antimonic  acid  by  this 
method).  The  arsenates  of  the  alkali-earth  metals  are  the 
most  troublesome  to  decompose ;  barium,  stronium,  and  cal- 
cium salts  usually  require  to  be  subjected  5  times  to  the  opera- 
tion, before  they  are  free  from  arsenic,  and  magnesium  arsenate 
it  is  impossible  thoroughly  to  decompose  in  this  way  (H. 
ROSE*).  According  to  SALKowsxif  barium  arsenate  may  be  . 
converted  into  chloride  quite  free  from  arsenic  by  one  ignition 
with  ammonium  chloride ;  however  calcium  arsenate  was  found 
to  leave  a  residue  containing  arsenic  acid  even  after  six  igni- 
tions with  ammonium  chloride. 

c.  MERCURY  FROM  GOLD  (SILVER,  AND  GENERALLY  FROM 
THE  NON-VOLATILE  METALS). 

Heat  the  weighed  alloy  in  a  porcelain  crucible,  ignite  till  142 
the  weight  is  constant,  and  determine  the  mercury  from  the 
loss.  If  it  desired  to  estimate  it  directly,  the  apparatus,  p.  307, 
fig.  54,  may  be  used.  In  cases  where  the  separation  of  mer- 
cury from  metals  that  oxidize  on  ignition  in  the  air  is  to  be 
effected  by  this  method,  the  operation  must  be  conducted  in 
an  atmosphere  of  hydrogen  (p.  251,  fig.  50). 

9.    Methods  based    on  the  Volatility  of  Arsenious 
Sulphide. 

ARSENIC  ACID  FROM  THE  OXIDES,  OF  MANGANESE,  IRON, 
ZINC,  COPPER,  NICKEL,  COBALT  (NOT  so  WELL  FROM  OXIDE  OF 
LEAD,  AND  NOT  FROM  OXIDES  OF  SILVER,  ALUMINUM,  OR  MAG- 
NESIUM). 

Mix  the  arsenic  acid  compound  (no  matter  whether  it  has  143 

*  Pogg.  Annal.  73,  582;  74,  578;  112,  173.       f  Journ.  f.  prakt,  Chem.  104,  138. 


566  SEPARATION.  [§  164. 

been  air-dried  or  gently  ignited)  with  sulphur,  and  ignite 
under  a  good  draught  in  an  atmosphere  of  hydrogen  (p.  251, 
fig.  50 ;  the  perforated  lid  must  in  this  case  be  of  porcelain ; 
platinum  would  not  answer).  The  whole  of  the  arsenic  vola- 
tilizes, the  sulphides  of  manganese,  iron,  zinc,  lead,  and  copper 
remain  behind ;  they  may  be  weighed  directly.  After  weigh- 
ing, add  a  fresh  quantity  of  sulphur  to  the  residue,  ignite  as 
before,  and  weigh  again ;  repeat  this  operation  until  the  weight 
remains  constant.  Usually,  if  the  compound  was  intimately 
mixed  with  the  sulphur,  the  conversion  of  the  arsenate  into 
sulphide  is  complete  after  the  first  ignition.  Results  very  good. 
In  separating  nickel  the  analyst  will  remember  that  the 
residue  cannot  be  weighed  directly,  since  it  does  not  possess  a 
constant  composition ;  hence  the  ignition  in  hydrogen  may  be 
saved ;  nickel  arsenate  loses  all  its  arsenic  on  being  simply 
mixed  with  sulphur  and  heated.  The  heat  should  be  moderate 
and  continued  till  no  more  red  sulphide  of  arsenic  is  visible 
on  the  inside  of  the  porcelain  crucible.  It  is  advisable  to  repeat 
the  operation.  The  separation  of  arsenic  from  cobalt  cannot 
be  completely  effected  in  this  manner  even  by  repeated  treat- 
ment with  sulphur,  but  it  can  be  effected  by  oxidizing  the  resi- 
due with  nitric  acid,  evaporating  to  dryness,  mixing  with  sul- 
phur, and  reigniting.  Smaltine  and  cobaltine  must  be  treated 
in  the  same  manner  (H.  HOSE*).  1  should  not  forget  to  men- 
tion that  EBELMEN,|  a  long  while  ago,  noticed  the  separation 
of  arsenic  acid  from  sesquioxide  of  iron  by  ignition  in  a  stream 
of  hydrogen  sulphide. 

10.  Method  based  upon  the  Separation  of  Arsenic  as 
Ammonium  Magnesium  Arsenate. 

ARSENIC  ACID  FROM  COPPER,  CADMIUM,  FERRIC  IRON,  MAN- 
GANESE, NICKEL,  COBALT,  ALUMINIUM. 

Mix  the  hydrochloric  acid  solution,  which  must  contain  144 
the  whole  of  the  arsenic  in  the   form  of  arsenic  acid,  with 
enough  tartaric  acid  to  prevent  precipitation  by  ammonia,  pre- 
cipitate the  arsenic  acid  according  to  §  127",  2,  as  ammonium 
magnesium  arsenate,  allow  to  settle,  filter,  wash  once  with  a 


*  Zeitschr.  f.  anal.  Chem.  1,  413. 

f  Annal.  de  Chim.  et  de  Phys.  (3)  25,  98. 


§  164.]  •         METALS   OF   GROUP   VI.  567 

mixture  of  3  parts  water  and  1  part  ammonia,  redissolve  in 
hydrochloric  acid,  add  a  very  minute  quantity  of  tartaric  acid, 
supersaturate  again  with  ammonia,  add  some  more  magnesium 
chloride  and  ammonium  chloride,  allow  to  deposit,  and  deter- 
mine the  now  pure  precipitate  according  to  §  127,  2.  In  the 
nitrate  the  bases  of  Groups  IV.  and  V.  may  be  precipitated  by 
ammonium  sulphide  ;  if  aluminium  is  present,  evaporate  the 
iiltrate  from  the  sulphides  with  addition  of  sodium  carbonate 
and  a  little  nitre  to  dryness,  fuse,  and  estimate  the  aluminium 
in  the  residue.  The  method  is  more  adapted  to  the  separation 
of  rather  large  than  of  very  small  quantities  of  arsenic  from  the 
above-named  metals,  since  in  the  case  of  small  quantities  the 
minute  portions  of  ammonium  magnesium  arsenate  that  remain 
in  solution  may  exercise  a  considerable  influence  on  the  accu- 
racy of  the  result. 

11.  Method  based  upon  the  Separation  of  Arsenic  as 
Ammonium  Arsenio-molybdate. 

ARSENIC  ACID  FROM  ALL  METALS  OF  GROUPS  I. — V. 

Separate  the  arsenic  acid   as  directed  in  §  127,  2,  I ;  long  145 
continued  heating  at  100°  is  indispensable.  The  determination 
•of  the  basic  metals  is  most  conveniently  effected  in  a  special 
portion. 

12.  Method  based  upon  the  Insolubility  of  Ferric 
~Arsenate. 

ARSEXIC  ACID  FROM  THE  METALS  OF  GROUPS  I.  AND  II., 

AND  FROM  ZlXC,  MANGANESE,  KlCKEL,  AND  COBALT. 

Mix  the  hydrochloric  solution  with  a  sufficient  quantity  of  146 
pure  ferric  chloride,  neutralize  the  greater  part  of  the  free 
acid  with  sodium  carbonate,  and  precipitate  the  iron  and  arse- 
nic acid  together  with  barium  carbonate  in  the  cold  or  with 
sodium  acetate  at  a  boiling  heat.  The  precipitate  should  be  so 
basic  as  to  have  a  brownish-red  color.  The  method  is  espe- 
cially suitable  for  the  separation  of  arsenic  acid  when  its  esti- 
mation is  not  required.  However,  the  precipitate  may  be  dis- 
solved in  hydrochloric  acid  and  the  arsenic  determined  by 
precipitation  with  hydrogen  sulphide. 


568  SEPARATION.  [§  164. 

13.  Methods   based  upon  the  Insolubility  of  some 
Chlorides. 

a.  SILVER  FKOM  GOLD. 

Treat  the  alloy  with  cold  dilute  nitrohydrochloric  acid,  147 
dilute,  and  filter  the  solution  of  auric  chloride  from  the  undis- 
solved  silver  chloride.     This  method  is  applicable  only  if  the 
alloy  contains  less  than  15  per  cent,  of  silver ;  for  if  it  contains 
a  larger  proportion,  the  silver  chloride  which  forms  protects 
the  undecomposed  part  from  the  action  of  the  acid.     In  the 
same  way  silver  may  be  separated  also  from  platinum. 

b.  MERCURY  FROM  THE   OXYGEN  COMPOUNDS  OF  ARSENIC 
AND  ANTIMONY. 

Precipitate  the  mercury  from  the  hydrochloric  solution  by  148 
means  of  phosphorous  acid  as  mercurous  chloride  (§  118,  2). 
The  tartaric  acid,  which  in  the  presence  of  antimony  must  be 

added,  does  not  interfere  with  the  reaction  (H.  KOSE*). 

• 

14.  Methods  based  upon  the  Insolubility  of  certain 
Sulphates  in  Water  or  Alcohol. 

a.  ARSENIC  ACID  FROM  BARIUM,  STRONTIUM,  CALCIUM,  AND 
LEAD. 

Proceed  as  for  the  separation  of  phosphoric  acid  from  the  149 
same  metals  (§  135,  b).  The  compounds  of  these  basic  radicals 
with  arsenious  acid  are  first  converted  into  arsenates,  before 
the  sulphuric  acid  is  added ;  this  conversion  is  effected  by 
heating  the  hydrochloric  acid  solution  with  potassium  chlo- 
rate or  by  means  of  bromine. 

b.  ANTIMONY  FROM  LEAD. 

Treat  the  alloy  with  a  mixture  of  nitric  and  tartaric  acids.  150 
The  solution  of  both  metals  takes  place  rapidly  and  with  ease. 
Precipitate  the  greater  part  of  the  lead  as  sulphate  (§  116,  3), 
filter,  precipitate  with  hydrogen  sulphide,  and  treat  the  sul- 
phides according  to  128,  with  ammonium  sulphide,  in  order 
to  separate  the  antimony  from  the  lead  left  unprecipitated  by 
the  sulphuric  acid  (A.  STRENGf). 

15.  Method  based  upon  the  Separation  of  Copper  as 
Cuprous  Sulphocyanate. 

COPPER  FROM  ARSENIC  AND  ANTIMONY. 

From  the  properly  prepared  solution  precipitate  the  cop-  151 

*  Pogg.  Annal.  110,  536.  f  Ding-  polyt.  Journ.  151,  389. 


§  165.]  METALS    OF   GROUP   VI.  569 

| 

per  by  §  119,  3,  5,  as  cuprous  'sulphocyanate,  allow  to  settle, 
filter,  wash  with  water  containing  ammonium  nitrate  (to  pre- 
vent the  washings  being  muddy),  and  determine  antimony 
and  arsenic  in  the  filtrate,  precipitating  first  with  hydrogen 
sulphide.  Results  good. 

16.  Method  'based  upon  the   different    deportment 
with  Cyanide  of  Potassium.. 

GOLD  FROM  LEAD  AND  BISMUTH. 

These  metals  may  be  separated  in  solution  by  potassium  152 
cyanide  in  the  same  way  in  which  the  separation  of  mercury 
from  lead  and  bismuth  is  effected  (see  110).  The  solution  of 
the  double  cyanide  of  gold  and  potassium  is  decomposed  by 
boiling  with  aqua  regia,  and,  after  expulsion  of  the  hydrocyanic 
acid,  the  gold  determined  by  one  of  the  methods  given  in 
§123. 


II.  SEPARATION  OF  THE  METALS  OF  THE  SIXTH  GROUP 

FROM    EACH    OTHEE. 

§165. 

INDEX.    (The  numbers  refer  to  those  in  the  margin.) 

Platinum  from  gold,  153,  168. 

tin,  antimony,  and  arsenic,  154. 
Gold  from  platinum,  153,  168. 

tin,  154,  167. 

"  antimony  and  arsenic,  154 

Tin  from  platinum,  154. 
gold,  154,  167. 

arsenic,  157,  162,  163,  164,  166,  169. 
antimony,  155,  158,  164,  165,  166. 
Tin  in  stannous,  from  tin  in  stannic  compounds,  172. 
Antimony  from  platinum  and  gold,  154. 
"  arsenic,  158.  159,  160. 

tin,  155,  158,  164,  165,  166. 
Antimony  of  antimonious  compounds  from 

antimonic  acid,  171. 
Arsenic  from  platinum  and  gold,  154. 

tin,  157,  162,  163.  164,  166,  169. 
antimony,  158,  159,  160. 
Arsenious  acid  from  arsenic  acid,  156,  161,  170. 


570  SEPARATION.  [§  165. 

1.  Method  based  upon  tfw  Precipitation  of  Plati- 
num as  Potassium  Platinic  Chloride. 

PLATINUM  FROM  GOLD. 

Precipitate  from  the  solution  of  the  chlorides  the  plati-  153 
num  as  directed  §  124,  £,  and  determine  the  gold  in  the  filtrate 
as  directed  §  123,  I. 

2.  Methods  based  upon  the  Volatility  of  the  Chlo- 
rides of  the  inferior  Metals. 

a.  PLATINUM  AND  GOLD  FROM  TIN,  ANTIMONY,  AND  ARSENIC. 
Heat  the  finely  divided  alloy  or  the  sulphides  in  a  stream  154 

of  chlorine  gas.     Gold  and  platinum  are  left,  the  chlorides  of 
the  other  metals  volatilize  (compare  121). 

b.  ANTIMONY  FROM  TIN. 

The  tin  should  be  present  wholly  as  a  stannous  salt.  155 
Precipitate  with  hydrogen  sulphide,  filter  (preferably  through 
an  asbestos  filtering  tube),  dry  the  precipitate,  and  pass  through 
it  a  current  of  dry  hydrochloric  gas  at  the  ordinary  tempera- 
ture. The  sulphides  are  converted  into  the  corresponding 
chlorides ;  the  chloride  of  antimony  alone  escapes,  and  may 
be  received  in  water.  Dissolve  the  residual  stannous  chloride 
in  water  containing  hydrochloric  acid,  and  estimate  the  tin 
according  to  §  126  (C.  TOOKEY*).  The  method  can  only  be 
used  in  rare  cases,  as  it  is  difficult  to  obtain  a  precipitate  quite 
free  from  stannic  sulphide. 

c.  ARSENIOUS  ACID  FROM  ARSENIC  ACID. 

The  amount  of  substance  taken  should  not  contain  more  156 
than  -2  grm.  arsenious  acid.  Heat  with  45  grm.  sodium 
chloride,  135  grm.  sulphuric  acid  (free  from  arsenic)  of  1*61 
sp.  gr.,  and  30  grm.  water  in  a  tubulated  retort  containing  a 
spiral  of  platinum,  and  provided  with  a  thermometer.  The 
temperature  should  rise  to  about  125°.  In  order  to  condense 
the  arsenious  chloride  in  the  products  of  distillation,  a  LIEBIG'S 
condenser  is  connected  with  the  retort ;  a  tubulated  receiver 
is  connected  with  the  condenser ;  a  U-tube  is  connected  with 
the  receiver,  and  finally  a  calcium  chloride  tube  containing 
fragments  of  glass  moistened  with  weak  soda  solution  is  fixed 

*  Journ.  Chem.  Soc.  15,  462. 


§  165.]  METALS   OF   GROUP    VI.  571 

upright  in  the  exit  end  of  the  U-tube.  In  the  receiver  and 
IJ-tube  water  is  placed.  At  the  end  of  the  operation  rinse 
the  calcium  chloride  tube,  and  mix  with  the  contents  of  the 
receiver.  Determine  the  arsenic  in  the  distillate  according  to 
jj  127,  -1,  #,  in  the  residue  according  to  §  127,  4,  h.  The  sul- 
phide obtained  from  the  former  corresponds  to  the  arsenious. 
acid,  from  the  latter  to  the  arsenic  acid.  Results  satisfactory 
(RiECKHER*).  If  the  substance  given  is  a  dilute  fluid,  render 
slightly  alkaline  with  sodium  carbonate,  and  concentrate  to 
about  20  c.c.,  finally  in  a  tubulated  retort. 

3.  Mrfltin/H   based  upon  the  Volatility  of  Arsenic 

am/  A  /•*>  /tious  Sulphide. 

a.  AKSKXIC  FROM  Tix  (H.  ROSE). 

Convert  into  sulphides  or  oxides,  dry  at  100°,  and  heat  a  157 
weighed  portion  with  addition  of  a  little  sulphur  in  a  bulb- 
tube,  gently  at  first,  but  gradually 'more  strongly,  conducting 
a  stream  of  dry  hydrogen  sulphide  gas  through  the  tube 
during  the  operation.  Sulphur  and  arsenious  sulphide  vola- 
tilize ;  sulphide  of  tin  is  left.  The  arsenious  sulphide  is 
received  in  U-tubes  containing  dilute  ammonia,  which  are 
connected  with  the  bulb-tube  in  the  manner  described  in  121. 
When  upon  continued  application  of  heat  no  sign  of  further 
sublimation  is  observed  in  the  colder  part  of  the  bulb-tube, 
drive  off  the  sublimate  which  has  collected  in  the  bulb,  allow 
the  tube  to  cool,  and  then  cut  it  off  above  the  coating.  Divide 
the  separated  portion  of  the  tube  into  pieces,  and  heat  these 
with  a  little  solution  of  soda  until  the  sublimate  is  dissolved ; 
unite  the  solution  with  the  ammoniacal  fluid  in  the  receivers, 
add  hydrochloric  acid,  then,  without  filtering,  potassium 
chlorate,  and  heat  gently  until  the  arsenious  sulphide  is  com- 
pletely dissolved.  Filter  from  the  sulphur,  and  determine  the 
arsenic  acid  as  directed  §  127,  2.  The  quantity  of  tin  cannot 
be  calculated  at  once  from  the  blackish-brown  sulphide  of  tin 
in  the  bulb,  since  this  contains  more  sulphur  than  SnS.  It  is 
therefore  weighed,  and  the  tin  determined  in  a  weighed  por- 
tion of  it,  by  converting  it  into  stannic  oxide,  which  is  effected 
by  moistening  with  nitric  acid,  and  roasting  (§  126,  1,  c). 

*  Pharm.  Centrallialle,  11.  92. 


572  SEPARATION.  [§  165. 

Tin  and  arsenic  in  alloys  are  more  conveniently  converted 
into  oxides  by  cautious  treatment  with  nitric  acid.  If,  how- 
ever, it  is  wished  to  convert  them  into  sulphides,  this  may 
readily  be  effected  by  heating  1  part  of  the  finely  divided 
alloy  with  5  parts  of  sodium  carbonate  and  5  parts  of  sulphur, 
in  a  covered  porcelain  crucible  until  the  mass  is  in  a  state  of 
calm  fusion.  It  is  then  dissolved  in  water,  the  solution  filtered 
from  the  ferrous  sulphide,  &c.,  which  may  possibly  have 
formed,  and  then  precipitated  with  hydrochloric  acid. 

If  the  tin  only  in  the  alloy  is  to  be  estimated  directly, 
while  the  arsenic  is  to  be  found  from  the  difference,  convert 
as  above  directed  into  sulphides  or  oxides,  mix  with  sulphur 
and  ignite  in  a  porcelain  crucible  with  perforated  cover  in 
a  stream  of  hydrogen  sulphide.  The  residual  arsenic-free 
stannous  sulphide  is  to  be  converted  into  stannic  oxide  and 
weighed  as  such. 

4.  Methods  based  upon  the  Insolubility  of  Sodium 
Metantimonate. 

a.  ANTIMONY  FROM  TIN  AND  ARSENIC  (H.  ROSE). 

If  the  substance  is  metallic,  oxidize  the  finely  divided  158 
weighed  sample,  in  a  porcelain  crucible,  with  nitric  acid  of 
1'4  sp.  gr.,  adding  the  acid  gradually.  Dry  the  mass  on  the 
water-bath,  transfer  to  a  silver  crucible,  rinsing  the  last 
particles  adhering  to  the  porcelain  into  the  silver  crucible 
with  solution  of  soda,  dry  again,  add  eight  times  the  bulk  of 
the  mass  of  solid  sodium  hydroxide,  and  fuse  for  some  time. 
Allow  the  mass  to  cool,  and  then  treat  with  hot  water  until 
the  undissolved  residue  presents  the  appearance  of  a  fine 
powder ;  dilute  with  some  water,  and  add  one-third  the  volume 
of  alcohol  of  '83  sp.  gr.  Allow  the  mixture  to  stand  for  24r 
hours,  with  frequent  stirring;  then  filter,  transfer  the  last 
adhering  particles  from  the  crucible  to  the  filter  by  rinsing 
with  dilute  alcohol  (1  vol.  alcohol  to  3  vol.  water),  and  wash 
the  undissolved  residue  on  the  filter,  first  with  alcohol  diluted 
with  twice  its  volume  of  water,  then  with  a  mixture  of  equal 
volumes  of  alcohol  and  water,  and  finally  with  a  mixture  of 
3  vol.  alcohol  and  1  vol.  water.  Add  to  each  of  the  alcoholic 
fluids  used  for  washing  a  few  drops  of  solution  of  sodium 
carbonate.  Continue  the  washing  until  the  color  of  a  portion 


§  165.]  METALS   OF   GROUP   VI.  573 

of  the  fluid  running  off  remains  unaltered  upon  being  acidified 
with  hydrochloric  acid  and  mixed  with  hydrogen  sulphide 
water. 

Rinse  the  sodium  metantimonate  from  the  filter,  wash  the 
latter  with  a  mixture  of  hydrochloric  and  tartaric  acids,  dis- 
solve the  metantimonate  in  this  mixture,  precipitate  with 
hydrogen  sulphide,  and  determine  the  antimony  as  directed 
§  125,  1.  In  presence  of  much  tin  it  is  well  to  fuse  the 
metantimonate  again  with  caustic  soda,  &c. 

To  the  filtrate,  which  contains  the  tin  and  arsenic,  add 
hydrochloric  acid,  which  produces  a  precipitate  of  stannic 
arsenate ;  conduct  now  into  the  unfiltered  fluid  hydrogen 
sulphide  for  some  time,  allow  the  mixture  to  stand  at  rest 
until  the  odor  of  that  gas  has  almost  completely  gone  off,  and 
separate  the  weighed  sulphides  of  the  metals  which  contain 
free  sulphur,  as  in  157. 

If  the  substance  contains  only  antimony  and  arsenic,  the 
alcoholic  filtrate  is  heated,  with  repeated  addition  of  water, 
until  it  scarcely  retains  the  odor  of  alcohol ;  hydrochloric  acid 
is  then  added,  and  the  arsenic  acid  determined  as  magnesium 
pyroarsenate  (§  127,  2),  or  as  arsenious  sulphide  (§  127,  4,  b). 

b.  Small  quantities  of  the  sulphides  of  arsenic  and  anti-  159 
mony  mixed  with  sulphur  are  often  obtained  in  mineral 
analysis.  The  two  metals  may  in  this  case  be  conveniently 
separated  as  follows  : — Exhaust  the  precipitate  with  bisulphide 
of  carbon,  oxidize  with  chlorine-free  red  fuming  nitric  acid, 
evaporate  the  solution  nearly  to  dryness ;  mix  the  residue  with 
a  copious  excess  of  sodium  carbonate,  add  some  sodium  nitrate, 
and  treat  the  fused  mass  as  given  in  #,  158.  If,  on  the  other 
hand,  you  have  a  mixture  of  sulphides  of  tin  and  antimony 
to  analyze,  oxidize  it  with  nitric  acid  of  1*5  sp.  gr.,  and  treat 
the  residue  obtained  on  evaporation  as  given  in  a,  158. 

5.  Methods  based  upon  the  Precipitation  of  Arsenic 
as  Ammonium  Magnesium  Arsenate. 

a.  ARSENIC  FROM  ANTIMONY. 

Oxidize  the  metals  or  sulphides  with  nitrohydrochloric  acid,  160 
with  hydrochloric  acid  and  potassium  chlorate,  with  bromine 
dissolved  in  hydrochloric  acid,  or  with  chlorine  in  alkaline  solu- 
tion ;  add  tartaric  acid,  a  large  quantity  of  ammonium  chloride, 


574  SEPARATION.  [§  165. 

and  then  ammonia  in  excess.  (Should  the  addition  of  the 
latter  reagent  produce  a  precipitate,  this  is  a  proof  that  an 
insufficient  quantity  of  ammonium  chloride  or  of  tartaric  acid 
has  been  used,  which  error  must  be  corrected  before  proceed- 
ing with  the  analysis.)  Then  precipitate  the  arsenic  acid  as 
directed  §  127,  2,  and  determine  the  antimony  in  the  filtrate 
as  directed  in  §  125,  1.  As  basic  magnesium  tartrate  might 
precipitate  with  the  ammonium  magnesium  arsenate,  the 
precipitate  should  always,  after  slight  washing,  be  redissolved 
in  hydrochloric  acid,  and  reprecipitated  with  ammonia  with 
addition  of  a  little  magnesia  mixture — an  excellent  method. 

b.  ARSENIOUS  ACID  FROM  ARSENIC  ACID. 

Mix  the  sufficiently  dilute  solution  with  a  large  quantity  161 
of  ammonium  chloride,  precipitate  the  arsenic  acid  as  directed 
§  127,  2,  and  determine  the  arsenious  acid  in  the  filtrate  by 
precipitation  with  hydrogen  sulphide  (§127, 4).  LUDWIG*  has 
observed  that  if  the  solution  is  too  concentrated,  magne- 
sium arsenite  falls  down  with  the  ammonium  magnesium 
arsenate,  hence  it  is  necessary  to  dissolve  the  weighed  magne- 
sium precipitate  in  hydrochloric  acid  and  test  the  solution  with 
hydrogen  sulphide.  The  presence  of  arsenious  acid  will  be 
betrayed  by  the  immediate  formation  of  a  precipitate. 

c.  TIN  AND  ANTIMONY  FROM  ARSENIC  ACID. 

LENSSEN-J-  separated  tin  from  arsenic  acid  with  good  162 
results  by  digesting  the  oxides  obtained  by  oxidation  with 
nitric  acid  wTith  ammonia  and  yellow  ammonium  sulphide,  and 
precipitating  the  arsenic  acid  from  the  clear  solution  accord- 
ing to  127,  2,  as  ammonium  magnesium  arsenate.  On  acidify- 
ing the  filtrate  the  tin  separates  as  stannic  sulphide.  The 
method  can  only  give  good  results  when  the  whole  of  the 
arsenic  was  present  as  arsenic  acid  before  the  addition  of 
ammonium  sulphide,  for  the  arsenic  in  a  solution  of  arsenious 
acid  in  yellow  ammonium  sulphide  is  not  thrown  down  by 
magnesia  mixture.  The  method  also  answers  for  separating 
antimony  from  arsenic. 

*  Archiv  fur  Pharm.  97,  24.  \  Annal.  d.  Chem.  u.  Pharm.  114,  116. 


§  165.]  METALS   OF   GROUP   VI.  575 

6.  Methods  based  on  the  different  behavior  of  the 
freshly  Precipitated  Sulphides  towards  Solution  of 
Potassium  Hydrogen  Sulphite  or  Oxalic  Acid. 

a.  ARSENIC  FROM  ANTIMONY  AND  TIN  (BuxsEN*). 

If  freshly  precipitated  arsenious  sulphide  is  digested  with  163 
sulphurous  acid  and  potassium  sulphite,  the  precipitate  is  dis- 
solved ;  on  boiling,  the  fluid  becomes  turbid  from  separated 
sulphur,  which  turbidity  for  the  most  part  disappears  again  on 
long  boiling.  The  fluid  contains,  after  expulsion  of  the  sul- 
phurous acid,  potassium  arsenite  and  thiosulphate.  The  sul- 
phides of  antimony  and  tin  do  not  exhibit  this  reaction.  Both 
therefore  may  be  separated  from  arsenious  sulphide  by  diluting 
the  solution  of  the  three  sulphides  in  potassium  sulphide  to  about 
500  c.c.  and  precipitating  with  a  large  excess  (about  a  litre)  of 
saturated  aqueous  sulphurous  acid,  digesting  the  whole  for 
some  time  in  a  water-bath,  and  then  boiling  till  one-third  of 
the  water  and  the  whole  of  the  sulphurous  acid  are  expelled 
and  the  sulphur  has  disappeared ;  this  will  take  about  an  hour 
and  a  half.  The  residuary  sulphide  of  antimony  or  tin  is  arsenic- 
free,  the  filtrate  contains  the  whole  of  the  arsenic  and  may  be 
immediately  precipitated  with  hydrogen  sulphide.  BUNSEN 
determines  the  arsenic  by  oxidizing  the  dried  sulphide  together 
with  the  filter  with  fuming  nitric  acid,  diluting  the  solution 
a  little,  warming  gently  with  a  little  potassium  chlorate  (in 
order  to  oxidize  more  fully  the  substances  formed  from  the 
paper),  and  finally  precipitating  as  ammonium  magnesium 
arsenate. 

With  regard  to  the  separation  of  stannic  sulphide  from 
the  solution  of  potassium  arsenite,  it  is  to  be  observed  that  the 
stannic  sulphide  must  be  washed  with  concentrated  solution 
of  sodium  chloride,  as,  if  water  were  used,  the  fluid  would  run 
through  turbid.  As  soon  as  the  precipitate  is  thoroughly 
washed  with  the  sodium  chloride,  the  latter  is  displaced  by 
solution  of  ammonium  acetate,  containing  a  slight  excess  of 
acetic  acid.  These  last  washings  must  not  be  added  to  the 
first,  as  the  ammonium  acetate  hinders  the  complete  precipita 
tion  of  the  arsenious  acid  by  hydrogen  sulphide. 

*  Annal.  d.  Chem.  u.  Pharm.  106,  3. 


576  SEPARATION.  L 

The  test-analyses  adduced  by  BUNSEN  show  very  satisfac- 
tory results. 

b.    TlN  FROM  ARSENIC  AND  ANTIMONY  (F.  W.  CLARKE*). 

Moist  freshly  precipitated  bisulphide  of  tin  completely  dis- 
.solves  on  boiling  for  a  moderate  length  of  time  with  excess  of 
oxalic  acid,  and  therefore  tin  in  the  form  of  bichloride  is  not 
thrown  down  by  hydrogen  sulphide  from  a  hot  solution 
containing  excess  of  oxalic  acid.  The  sulphides  of  arsenic  are 
barely  affected  by  boiling  with  oxalic  acid,  and  hydrogen 
sulphide  immediately  reprecipitates  the  traces  dissolved. 
Sulphide  of  antimony  dissolves  more  copiously  on  boiling 
with  oxalic  acid,  but  hydrogen  sulphide  reprecipitates  the 
antimony  from  the  solution. 

[These  reactions  form  the  basis  of  CLARKE'S  method,  which, 
with  some  important  modifications,  has  been  successfully 
applied  to  the  separation  of  tin  from  antimony  in  alloys  by  F. 
P.  DEWEY,f  who  proceeds  as  follows : 

Dissolve  with  a  mixture  of  1  part  strong  nitric  acid,  4  parts 
strong  hydrochloric  acid,  and  5  parts  water.  Since  even  small 
quantities  of  free  mineral  acids  prevent  complete  precipitation 
of  antimony,  they  are  removed  by  evaporating  to  dryness  on 
a  water-bath,  with  previous  addition  of  enough  potassium 
chloride  to  form  double  salts  with  the  tin  and  antimony  chlor- 
ides present.  The  presence  of  the  potassium  chloride  entirely 
prevents  loss  of  tin  and  antimony  by  volatilization  as  chlorides 
during  the  evaporation.  Add  to  the  salts  thus  obtained  a 
large  quantity  of  pure  oxalic  acid  (at  least  20  parts  crystallized 
acid  to  1  part  tin),  and  dilute  with  water  to  about  125  c.c.  per 
*1  grin,  antimony  present.  The  salts  dissolve  readily.  Boil  and 
pass  H2S  through  the  boiling  solution  half  an  hour.  Filter 
immediately  while  hot,  and  wash  the  greater  part  of  the  soluble 
matter  out  of  the  precipitate  with  hot  water.  The  precipi- 
tated antimonious  sulphide  will  contain  a  little  stannic  sulphide. 
Dissolve  in  ammonium  sulphide,  avoiding  an  unnecessary 
quantity  of  the  solvent,  and  pour  the  solution  into  a  strong  hot 
solution  of  oxalic  acid.  A  liberal  excess  of  oxalic  acid  should 
be  present  after  decomposition  of  the  sulphur  salts.  Heat  the 
oxalic  solution  with  the  suspended  precipitate  of  antimonious 

*  Chem.  News,  21,  124.  f  Am.  Chem.  Journ.  i.  244. 


£165.]  METALS    OF   GROUP   VI.  577 

sulphide  to  boiling,  and  pass  H,S  gas  ten  minutes.  Collect  the 
SbaS,  now  free  from  tin  on  a  weighed  filter,  wash  with  hot 
water,  and  proceed  to  determine  the  antimony  as  directed  in  § 

125,  1,  b.     To  recover  tin  from  the  filtrate,  evaporate  nearly  to 
dryness,  add  strong  sulphuric  acid,  and  heat  till  all  the  oxalic 
acid  present  is  decomposed  and  removed.     Dilute  largely,  and 
precipitate   the  tin  with  hydrogen  sulphide  according  to  § 

126,  1,  c.-] 

7.  Methods  based  'upon  the  Separation  of  the  Metals 
themselves,  or,  as  the  case  may  be,  on  the  different 
deportment  of  the  same  with  Acids. 

a.  TIN    FROM    ANTIMONY    (TooKEY,*    improvements    by 
CLASEN  (loc.  cit.)  and  AirFiELDf). 

The  hydrochloric  solution  should  be  oxidized  if  necessary  165 
with  a  few  drops  of  nitric  acid  or  a  little  potassium  chlorate. 
Heat  nearly  to  boiling  and  add  iron  as  long  as  it  dissolves. 
Either  hoop-iron  or  fine  bright  wire  will  answer  the  purpose ; 
it  should  dissolve  in  dilute  hydrochloric  acid,  leaving  little  or 
no  residue.  The  antimony  will  be  thrown  down,  the  tin 
reduced  to  stannous  chloride.  As  soon  as  all  antimony  appears 
to  be  precipitated  and  the  iron  to  be  dissolved,  add  more 
hydrochloric  acid,  allow  to  deposit,  decant  and  test  whether 
iron  produces  any  further  precipitate.  In  this  way  you  will 
ensure  the  absence  of  any  metallic  iron  and  the  complete  pre- 
cipitation of  the  antimony.  Wash  the  antimony  with  hot 
water,  which  should  be  at  first  acidified,  then  with  alcohol, 
finally  with  ether,  drying  at  100°.  Throw  down  the  tin  with 
hydrogen  sulphide  (§  126,  1,  c).  With  care  the  results  are 
good ;  compare  CLASEN  (loc.  cit.). 

b.  MUCH  TIN  FROM  LITTLE  ANTIMONY  AND  ARSENIC. 

If  an  alloy  of  the  three  metals  is  treated  in  a  very  finely  166 
divided  condition  in  a  stream  of  carbonic  acid  with  strong 
hydrochloric  acid,  the  whole  of  the  tin  dissolves  to  stannous 
chloride.  A  part  of  the  arsenic  and  antimony  escapes  as 
arsenetted  and  antimonetted  hydrogen,  whilst  the  rest  remains 
behind  in  the  state  of  metal,  or,  as  the  case  may  be,  of  a  solid 
combination  with  hydrogen.  Conduct  the  gas  through  several 

*  Journ.  Chem.  Soc.  15,  402.  f  Zeitsckr.  f.  anal.  Chem.  9,  107. 


578  SEPARATION.  [§  165, 

XT-tubes,  containing  a  little  chlorine-free  red  fuming  nitric 
acid,  whereby  the  arsenic  and  antimony  will  be  oxidized. 
When  the  solution  is  effected,  dilute  the  contents  of  the  flask 
with  air-free  water  to  a  certain  volume,  mix,  allow  to  settle, 
and  determine  the  tin  in  an  aliquot  part,  either  gravimetrically 
or  volumetrically.  Filter  the  rest  of  the  fluid,  wash  the  pre- 
cipitate thoroughly,  dry  the  filter  with  its  contents  in  a  porce- 
lain crucible,  add  the  contents  of  the  U-tubes,  evaporate  to 
dryness,  and  in  the  residue  separate  the,  antimony  and  arsenic 
as  directed  158.  It  is  well  to  treat  an  aliquot  part  of  the 
hydrochloric  solution  with  iron  (165)  to  find,  and,  if  necessary, 
estimate  traces  of  antimony  which  may  have  passed  into  the 
hydrochloric  acid  solution. 

c.  TIN  FROM  GOLD. 

Gold  may  be  separated  from  excess  of  tin  by  boiling  the  167 
finely  divided  alloy  with  only  slightly  diluted  sulphuric  acid, 
to  which  hydrochloric  acid  has  been  cautiously  added.  The 
tin  dissolves  as  stannous  chloride.  Heat  is  applied  till  the 
sulphuric  acid  begins  to  volatilize  copiously.  Stannic  oxide 
is  formed  which  dissolves  in  the  concentrated  sulphuric  acid, 
while  the  gold  remains  behind.  On  addition  of  much  water,, 
the  stannic  oxide  falls,  mixed  with  finely  divided  gold,  in  th 
form  of  a  purple-red  precipitate.  On  warming  with  concen- 
trated sulphuric  acid,  the  stannic  oxide  finally  redissolves, 
while  the  gold  is  left  pure  (H.  HOSE*). 

d.  PLATINUM  FROM  GOLD. 

The  aqua  regia  solution  is  freed  as  far  as  possible  from  168 
nitric  acid  by  evaporation  with  hydrochloric  acid,  and  treated 
with  a  solution  of  ferrous  chloride,  the  gold  being  determined 
as  directed  §  123,  &.     The  platinum  may  be  precipitated  from 
the  filtrate  by  hydrogen  sulphide  according  to  §  124,  c. 

8.  Method  based  upon  the  Precipitation  of  Tin  as 
Stannic  Arsenate. 
TIN  FROM  ARSENIC. 

E.  HlFFELYf  has  proposed  the  following  method  of  deter-  169 
mining  both  the  tin  and  the  arsenic  in  commercial  sodium 
stannate,  which  often  contains  a  large  admixture  -of  sodium 

*  Pogg.  Annal.  112,  172.  f  Phil.  Mag.  10,  220. 


§  165.]  METALS    OF   GROUP   VI.  -579 

arsenate.  Mix  a  weighed  sample  with  a  known  quantity  of 
sodium  arsenate  in  excess,  add  nitric  acid  also  in  excess,  boil, 
filter  off  the  precipitate,  which  has  the  composition  2SnO3,  As, 
O6  -\-  10H2O,  and  wash ;  expel  the  water  by  ignition,  and 
weigh  the  residue,  which  consists  of  2SnOa,AsaO5.  In  the 
filtrate  determine  the  excess  of  arsenic  acid  .as  directed  §  127, 
2.  The  amount  of  the  stannic  oxide  is  found  from  the  weight 
of  the  precipitate,  that  of  the  arsenic  acid  is  obtained  by  add- 
ing the  quantity  in  the  precipitate  to  the  quantity  in  the  fil- 
trate, and  deducting  the  quantity  added. 

9.  Volumetric  Methods. 

a.  AKSENIOUS  FROM  ARSENIC  Aero. 

Convert  the  whole  of  the  arsenic  in  a  portion  of  the  sub-  170 
stance  into  arsenic  acid  and  determine  the  total  amount  of  this 
as  directed  §  127,  2  ;  determine  in  another  portion  the  arseni- 
ous  acid  as  directed  in  §  127,  5,  #,  and  calculate  the  arsenic 
acid  from  the  difference. 

&.  ANTIMONY  OF  ANTIMONIOUS  COMPOUNDS  FROM  ANTIMONIO 
ACID. 

Determine  in  a  sample  of  the  substance  the  total  amount  171 
of  the  antimony  as  directed  §  125,  1,  in  another  portion  esti- 
mate the  antimony  present  as  an  antirnonious  compound  as 
directed  §  125,  3,  and  calculate  the  antiinonic  acid  from  the 
difference. 

c.  TIN  OF  STANNOUS,  FROM  TIN  OF  STANNIC  COMPOUNDS. 

In  one  portion  of  the  substance  convert  the  whole  of  the  172 
stannous  into  stannic  salts  by  digestion  with  chlorine  water  or 
some  other  means,  and  determine  the  total  quantity  of  tin  as 
directed  §  126,  1,  b ;  in  another  portion,  which,  if  necessary, 
is -to  be  dissolved  in  hydrochloric  acid  in  a  stream  of  carbonic 
acid,  determine  the  stannous  tin  according  to  §  126,  2. 

II.   SEPARATION  OF  THE  ACIDS  FROM  EACH  OTHER. 

It  must  not  be  forgotten  that  the  following  methods  of 
separation  proceed  generally  upon  the  assumption  that  the 
acids  exist  either  in  the  free  state,  or  as  alkali  salts ;  compare  the 
introductory  remarks,  p.  479.  Where  several  acids  are  to  be 
determined  in  one  and  the  same  substance,  we  very  often  use 


580  SEPARATION.  [§  166. 

a  separate  portion  for  each.  The  methods  here  given  do  not 
embrace  every  imaginable  case,  but  only  the  most  important 
cases,  and  those  of  most  frequent  occurrence. 


First  Group. 

ARSENIOUS  ACID ARSENIC    ACID — CHROMIC    ACID SULPHURIC    ACID 

PHOSPHORIC     ACID — BORACIC    ACID OXALIC     ACID HYDROFLUORIC 

ACID — SILICIC    ACID CARBONIC    ACID. 

§166. 

1.  ARSENIOUS  ACID  AND  ARSENIC  ACID  FROM  ALL  OTHER 
ACIDS. 

Precipitate  the  arsenic  from  the  solution  by  hydrogen  sul-  173 
phide  (§  127,  4,  a  or  &),  filter,  and  determine  the  other  acids 
in  the  filtrate.  It  must  be  remembered,  that  the  arsenious 
sulphide  will  be  obtained  mixed  with  sulphur  if  chromic  acid, 
ferric  salts,  or  any  other  substances  which  decompose  hydro- 
gen sulphide  are  present.  The  estimation  of  sulphuric  acid 
in  the  filtrate  cannot  be  accurate  unless  air  is  excluded,  and 
oxidizers  such  as  chromic  acid  are  absent ;  sulphuric  acid  is, 
therefore,  best  estimated  in  a  separate  portion  (174).  From 
those  acids  which  form  soluble  magnesium  salts,  arsenic  acid 
may  be  separated  also  by  precipitation  as  ammonium  magne- 
sium arsenate  (§  127,  2). 

2.  SULPHURIC  ACID  FROM  ALL  THE  OTHER  ACIDS.* 
a.  From  Arsenious,  Arsenic,  Phosphoric^  Boracic,0xalic, 

and  Carbonic  Acids. 

Acidify  the  dilute  solution  strongly  with  hydrochloric  acid,  174 
mix  with  barium  chloride,  and  filter  the  barium  sulphate  from 
the  solution,  which  contains  all  the  other  acids.  Determine 
the  barium  sulphate  as  directed  §  132.  If  acids  are  present' 
with  which  barium  forms  salts  insoluble  in  water  but  soluble 
in  acids,  the  barium  sulphate  is  apt  to  carry  down  with  it  such 
salts,  and  this  is  all  the  more  liable  to  happen,  the  longer  the 


*  With  respect  to  the  separation  of  sulphuric  acid  from  selenic  acid,  comp. 
WOHLWILL  (Annal.  d.  Chem.  u.  Pharm.  114,  183). 

f  If  metaphosphoric  acid  is  present,  it  must  first  be  converted  into  orthophos- 
phoric  by  fusion  with  alkali  carbonate. 


§  166.]  ACIDS    OF   GROUP   I.  581 

precipitate  is  allowed  to  settle.  This  remark  applies  especially 
to  barium  oxalate,  and  tartrate,  and  the  barium  salts  of 
other  organic  acids  (H.  ROSE).  In  such  cases  I  would  recom- 
mend, after  washing,  to  stop  up  the  neck  of  the  funnel,  and 
digest  the  precipitate  with  a  solution  of  hydrogen  sodium  car- 
bonate, then  to  wash  with  water,  with  dilute  hydrochloric 
acid,  and  again  with  water.  In  every  case,  however,  the 
purity  of  the  weighed  barium  sulphate  must  be  tested  as 
directed  §  132,  1. 

In  the  fluids  filtered  from  the  barium  sulphate  the  other 
acids  are  determined  according  to  the  directions  of  the  Fourth 
Section,  after  the  removal  of  the  excess  of  barium  chloride. 
Or  the  other  acids  may  be  estimated  in  separate  portions  of 
the  substance,  which  is  indeed  usually  the  best  way,  and  for 
carbonic  acid  is  of  course  the  only  way. 

~b.  From  Hydrofluoric  Acid. 

a.  When  sulphuric  acid  and  hydrofluoric  acid  are  present  175 
in  the  free  state  in  aqueous  solution,  it  is  best  to  estimate  the 
acidity  in  one  portion  by  means  of  standard  soda  (§  192),  and 
the  sulphuric  acid  in  another  (§  132,  L,  1),  finding  the  hydro- 
fluoric acid  by  difference.  The  barium  sulphate  should  be 
purified  by  fusion  with  sodium  carbonate  (§  132,  I.,  1). 

ft.  To  estimate  both  acids  in  minerals  or  other  dry  sub-  176 
stances,  it  is  safest,  provided  the  fluoride  can  be  decomposed 
by  sulphuric  acid,  to  determine  the  fluorine  in  one  portion 
according  to  §  138,  3,  «,  and  to  fuse  another  portion  for  a 
long  time  with  four  times  its  amount  of  sodium  carbonate, 
which  will  decompose  the  sulphate  thoroughly,  the  fluoride 
generally  but  partially.  The  fused  mass  is  soaked  in  water, 
the  solution  filtered,  acidified  with  hydrochloric  acid  and  pre- 
cipitated with  barium  chloride.  The  barium  sulphate  thus 
obtained  generally  contains  barium  fluoride,  and  must  be 
purified  according  to  §  132,  I.,  1,  by  fusion  with  sodium  car- 
bonate, &c. 

y.  An  actual  separation  of  both  acids  may  be  effected,   177 
when  both  are  in  the  form  of  alkali  salts,  by  adding  sodium 
carbonate  if  necessary,  and  then  precipitating   the   fluorine 
according  to  §  138,  I.,  adding  the  calcium  chloride  cautiously 
in  very  slight  excess.     The  sulphuric  acid  is  for  the  most  part 


£82  SEPARATION.  [§ 

found  in  the  filtrate  from  the  calcium  carbonate  and  fluoride, 
a  very  small  part  is  generally  also  found  in  the  calcium 
acetate  filtered  from  the  calcium  fluoride.  Both  filtrates  are 
acidified  and  precipitated  with  barium  chloride  (§  132,  I.,  1. 
H.  EOSE). 

d.  Insoluble  compounds  may  also  be  decomposed  by  fusion  178 
with  six  parts  of  sodium  and  potassium  carbonates,  and  two 
parts  of  silica.  The  fused  mass,  after  cooling,  is  treated  with 
water,  the  solution  is  mixed  with  ammonium  carbonate,  and 
heated,  more  ammonium  carbonate  is  added  to  replace  what 
evaporates,  the  silicic  acid  thrown  down  is  filtered  off  and 
washed  with  water  containing  ammonium  carbonate,  a  solu- 
tion of  zinc  oxide  in  ammonia  is  added  to  precipitate  the 
remaining  silica,  the  fluid  is  evaporated  till  all  ammonia  is 
driven  off,  filtered  and  the  process  concluded  as  in  y.  The 
precipitate  produced  by  the  zinc  should  be  tested  for  sulphuric 
acid. 

c.  From  Chromic  Acid. 

Boil  the  dry  compound  with  strong  hydrochloric  acid  179 
(p.  357,  ft)  and  estimate  the  chromic  acid  from  the  evolved 
chlorine.  Neutralize  some  of  the  acid  with  ammonia,  dilute 
and  precipitate  the  sulphuric  acid  by  long  boiling  with  excess 
of  barium  chloride.  The  barium  sulphate  thus  obtained 
retains  chromic  oxide  (H.  KOSE)  and  must  always  be  fused 
with  sodium  carbonate,  &c.  (p.  367). 

d.  From  Hydrofluosilicic  Acid. 

First  throw  down  the  hydrofluosilicic  acid  according  to  180 
§  133,  as  potassium  silicofluoride,  then  the  sulphuric  acid  in 
the  filtrate  with  barium  chloride. 

e.  From  Silicic  Acid. 
Compare  192. 

3.  PHOSPHORIC  ACID  FROM  THE  OTHER  ACIDS. 

a.  From  the  (icids  of  arsenic,  see  173 :  from  sulphuric  181 
acid,  see  174 ;  from  silicic  acid,  see  192. 

b.  From  Chromic  Acid. 

Precipitate   the   phosphoric   acid   by  adding   ammonium 
nitrate  and  ammonia,  and  then  magnesium  nitrate,  and  deter- 


§  166.  J  ACIDS    OF   GROUP   I.  583 

mine  the  chromic  acid  in  the  filtrate  as  directed  §  130,  I.,  #, 
ft  or  L,  b. 

c.  From  I>oracic  Acid. 

Precipitate  the  phosphoric  acid  with  a  solution  of  double  182 
•chloride  of  magnesium  and  ammonium  (§  134,  b,  a),  wash  the 
precipitate  partially,  redissolve  it  in  hydrochloric  acid,  repre- 
-cipitate  with  ammonia,  adding  a  little  magnesium  and  ammo- 
nium chloride,  and  estimate  the  phosphoric  acid  as  magnesium 
pyrophosphate.  In  the  filtrate  estimate  the  boracic  acid  as 
magnesium  borate  (§  136,  L,  1,  d). 

d.  From  Oxalic  Acid. 

a.  If  the  two  acids  are  to  be  determined  in  one  portion,  183 
the  aqueous  or  hydrochloric  solution  is  mixed  with  sodium 
:auric  chloride  in  excess,  heat  applied,  and  the  oxalic  acid  cal- 
culated from  the  reduced  gold  (§  137,  c).  The  gold  added  in 
excess  is  separated  from  the  filtrate  by  hydrogen  sulphide,  and 
the  phosphoric  acid  then  precipitated  by  double  chloride  of 
magnesium  and  ammonium. 

ft.  If  there  is  enough  of  the  substance,  the  oxalic  acid  is  184 
determined  in  one  portion  according  to  §  137,  &,  or  d,  and  the 
phosphoric  acid  in  another  portion.  If  the  substance  is  solu- 
ble in  water,  and  the  quantity  of  oxalic  acid  inconsiderable, 
the  phosphoric  acid  may  be  precipitated  at  once  with  magne- 
sium chloride,  ammonium  chloride,  and  ammonia :  if  not,  the 
substance  is  ignited  with  potassium  carbonate  and  sodium  car- 
bonate, and  the  oxalic  acid  being  thus  destroyed,  the  phos- 
phoric acid  is  determined  in  the  nitric  acid  solution  of  the 
residue  according  to  §  134,  L,  J,  ft. 

e.  From  Hydrofluoric  Acid. 

a.  Phosphates  and  fluorides  are  frequently  found  together  185 
in  minerals.  In  the  analysis  of  phosphorites,  for  instance,  we 
have  to  estimate  small  quantities  of  fluorine,  often  too  in  the 
presence  of  aluminium  and  iron,  which  increase  the  difficulty. 
According  to  my  own  experience,*  it  is  always  safest  in  such 
cases  to  estimate  in  one  portion  the  fluorine  as  silicon  fluoride 
(§  138,  II.,  3,  a),  and  in  another  portion  the  phosphoric  acid. 
Regarding  the  first  estimation,  it  must  be  mentioned  that  car- 

*  Zeitschr.  f.  anal.  Chem.  5,  190,  and  6,  403. 


584  SEPARATION.  [§  166. 

bonic  acid  if  present  must  first  be  removed.  To  this  end  heat 
the  finely  powdered  weighed  substance,  with  water,  add  acetic 
acid  in  slight  excess,  and  also,  if  the  fluoride  present  is  soluble 
in  water,  some  calcium  acetate  ;  evaporate  to  dry  ness  on  a  water 
bath,  treat  with  water,  filter,  wash  the  insoluble  matter,  dry, 
separate  as  far  as  possible  from  the  filter,  add  the  filter  ash, 
weigh,  test  a  small  portion  for  carbonic  acid  by  heating  with 
hydrochloric  acid,  and  weigh  the  rest  for  the  fluorine  estima- 
tion. For  the  estimation  of  the  phosphoric  acid,  dissolve  the 
finely  powdered  substance  in  hydrochloric  acid,  evaporate  to 
dryness  on  a  water-bath,  moisten  with  a  little  hydrochloric 
acid,  add  nitric  acid,  warm,  dilu-te,  filter,  evaporate  filtrate  and 
washings  to  dryness,  dissolve  in  nitric  acid,  and  proceed 
according  to  §  134,  I.,  £>,  ft. 

ft.  Where  you  have  an  alkali  phosphate  and  an  alkali  186 
fluoride  together  in  aqueous  solution  the  phosphoric  acid  may 
be  separated  according  to  §  135,  II.,  d,  ft,  as  silver  phosphate, 
or  according  to  §  135,  II.,  &,  as  mercurou&  phosphate.  The 
fluoride  will  be  all  in  the  filtrate.  If  the  former  method  is 
adopted  the  silver  is  removed  from  the  filtrate  by  sodium 
chloride,  and  the  fluorine  estimated  as  calcium  salt  (§  138, 1.). 
If  the  latter  method  is  adopted,  as  the  solution  is  always  acid, 
the  use  of  glass  and  porcelain  must  be  avoided.  The  mercury 
is  removed  from  the  filtrate  by  neutralizing  with  sodium  car- 
bonate and — without  filtering — passing  hydrogen  sulphide. 
The  fluorine  is  estimated  in  the  filtrate  as  calcium  salt,  accord- 
ing to  §  138,  I.  (II.  KOSE). 

y.  Substances  which  are  insoluble  in  water,  and  cannot  be  187 
decomposed  by  acids,  are  fused  with  sodium  carbonate  and 
silica  (178),  the  fused  mass  is  treated  with  water,  and  the  solu- 
tion with  ammonium  carbonate.  In  this  way  all  the  fluorine 
and  all,  or  nearly  all,  the  phosphoric  acid  will  be  brought  into 
solution.  The  solution  is  treated  as  in  186,  and  any  remainder 
of  phosphoric  acid  in  the  undissolved  residue  is  estimated 
according  to  185. 

4.  HYDROFLUORIC  ACID  FROM  OTHER  ACIDS. 
a.  fluorides  from  E orates. 

Mix  the  solution  containing  alkali  borate  and  fluoride  with  188 
some  sodium  carbonate,  and  add  calcium  acetate  in  excess.    A 


§  166.]  ACIDS    OF   GROUP   I.  585 

precipitate  is  formed,  which  contains  the  whole  of  the  fluorine 
as  calcium  fluoride,  and  besides  this,  calcium  carbonate  and 
some  calcium  borate ;  the  greater  portion  of  the  latter  having 
been  redissolved  by  the  excess  of  the  calcium  salt  added. 
Determine  the  calcium  fluoride  in  the  precipitate  as  directed 
§  138, 1.  The  small  quantity  of  boracic  acid  in  the  precipitate 
is,  in  this  process,  partly  volatilized,  partly  dissolved  after 
evaporating  the  mass  with  acetic  acid  and  extracting  with 
water.  It  is  therefore  necessary  to  determine  the  boracic  acid 
in  a  separate  portion  of  the  substance,  according  to  §  136,  I., 
2  (A.  STROMEYER).* 

b.  Fluorides  from  Silicic  Acid  and  Silicates. 

A  great  many  native  silicates  contain  fluorides :  care  must, 
therefore,  always  be  taken,  in  the  analysis  of  minerals,  not  to 
overlook  the  latter.  If  the  silicates  containing  fluoride  are 
decomposable  by  acids — which  is  only  rarely  the  case — and 
the  silicic  acid  is  separated  in  the  usual  way  by  evaporation, 
the  whole  of  the  fluorine  may  volatilize. 

a.  BERZELIUS'S  method.  Fuse  the  elutriated  substance  189 
with  4  parts  of  sodium  carbonate  for  some  time  at  a  strong 
red  heat,  digest  the  mass  in  water,  boil,  filter,  and  wash,  first 
with  boiling  water,  then  with  ammonium  carbonate.  The  fil- 
trate contains  all  the  fluorine  as  sodium  fluoride,  and,  besides 
this,  sodium  carbonate,  silicate,  and  aluminate.  Mix  the  fil- 
trate with  ammonium  carbonate  and  heat  the  mixture,  replac- 
ing the  ammonium  carbonate,  which  evaporates.  Filter  off 
the  precipitate  of  hydrate  of  silicic  acid  and  aluminium 
hydroxide,  and  wash  with  ammonium  carbonate.  To  separate 
the  last  portions  of  silica  from  the  filtrate  add  a  solution  of 
zinc  oxide  in  ammonia,  evaporate  till  no  more  ammonia 
escapes,  and  filter  off  the  precipitate  of  zinc  silicate  and  oxide. 
Determine  the  silica  in  this  precipitate  by  dissolving  in  nitric 
acid,  evaporating  to  dryness,  taking  up  wdth  nitric  acid,  and 
filtering  off  the  undissolved  silica.  In  the  alkaline  filtrate 
estimate  the  fluorine  as  calcium  salt  (§  138,  I.).  The  residue, 
insoluble  in  water,  and  the  precipitate  produced  by  ammonium 
carbonate  are  finally  treated  with  hydrochloric  acid  according 
to  §  140,  II.,  «,  in  order  to  separate  the  silica. 

*  Annal  d.  Chem.  u,  Pharm.  100,  91 


586  SEPARATION.  [§  166. 

ft.  In  substances  readily  decomposed  by  sulphuric  acid  you  190 
may  also  separate  and  weigh  the  silica  according  to  189  in  one 
portion,  and  determine  the  fluorine  in  another  portion  accord- 
ing to  §  138,  II.,  3,  a. 

c.  Fluorides,  /Silicates  and  Phosphates  together. 

Compounds  of  this  kind  are  not  rare  in  nature,  and  may  191 
be  decomposed  according  to  189.  We  cannot  always  rely  on 
complete  decomposition  of  the  phosphate,  as,  for  instance,  cal- 
cium phosphate  is  but  partially  decomposed  on  fusion  with 
sodium  carbonate.  The  solution,  obtained  after  separation  of 
the  silica  by  ammonium  carbonate  and  the  zinc  solution,  is 
made  up  to  a  definite  volume,  and  a  portion  is  tested  for  phos- 
phoric acid  with  molybdic  solution.  If  none  is  present  the 
fluorine  is  estimated  in  the  measured  remainder  of  the  fluid  as 
fluoride  of  calcium  (§  138,  I.).  If  on  the  other  hand  phos- 
phoric acid  is  still  present,  treat  the  measured  remainder  of  the 
fluid  according  to  186.  In  the  original  residue  and  the  ammo- 
nium carbonate  precipitate  estimate  the  principal  amounts  of 
the  silicic  and  phosphoric  acids  and  the  basic  metals.  In  the 
zinc  precipitate  estimate  the  remainder  of  the  silicic  acid,  and 
in  the  filtrate  from  the  latter  estimate  the  portion  of  the 
phosphoric  acid  which  was  thrown  down  by  zinc  oxide. 

As  the  phosphoric  acid  is  so  divided  by  this  method,  it  is 
well  to  make  a  direct  estimation  of  it  in  another  portion  of  the 
substance,  especially  when  only  a  small  quantity  is  present. 
For  this  purpose  decompose  the  silicate  with  hydrofluoric  and 
hydrochloric  acids,  add  enough  but  not  too  large  an  excess  of 
sulphuric  acid,  and  evaporate  till  all  the  fluorine  has  escaped  as 
silicon  fluoride  arid  hydrofluoric  acid.  Do  not  increase  the  heat 
to  the  escape  of  sulphuric  acid,  or  phosphoric  acid  may  be  lost. 
Take  up  the  residue  with  nitric  acid,  dilute,  filter,  and  estimate 
the  phosphoric  acid  in  the  filtrate  by  the  molybdic  method. 

If  the  substance  can  be  easily  decomposed  with  sulphuric 
acid,  the  fluorine  may  of  course  also  be  expelled  as  silicon 
fluoride  and  estimated  according  to  §  138,  II.,  3,  a. 

5.  SILICIC  Aero  FKOM  ALL  OTHER  ACIDS. 
a.  In  compounds  which  are  decomposed  by  hydrochloric 
field. 

Decompose  the  substance  by  digestion  with  hydrochloric  192 


§  166.]  ACIDS  OF  (iiioi'p  i.  587 

or  nitric  acid,  evaporate  the  whole  on  the  water  bath  to  dryness 
{§  140,  II.,  a),  treat  with  water,  hydrochloric  acid  or  nitric  acid 
according  to  circumstances,  filter  off  the  silica,  and  estimate 
the  other  acids  in  the  filtrate.  The  following  points  require 
attention. 

a.  In  the  presence  of  borates  or  fluorides  this  method  cannot 
be  used,  employ  193. 

ft.  In  the  presence  of  phosphoric  acid  the  silica  always 
retains  a  small  portion,  which  cannot  be  extracted  by  washing 
with  acidified  water  (H.  ROSE,  "W.  SKEY*).  After  washing 
the  silica  with  water,  treat  it  repeatedly  with  ammonia,  which 
will  leave  only  a  very  minute  quantity  of  the  phosphoric  acid. 
Evaporate  the  ammoniacal  fluid,  finally  adding  a  little  hydro- 
chloric acid,  dissolve  in  water  with  addition  of  a  little  nitric 
acid,  filter  off  the  small  amount  of  silica  which  was  taken  up 
by  the  ammonia,  and  estimate  the  remainder  of  the  phosphoric 
acid  in  the  filtrate. 

J.  In  compounds  which  are  not  decomposed  by  hydrochlo- 
ric acid. 

Fuse  with  carbonate  of  potash  and  soda  (p.  422),  and  treat  193 
the  residue  either  at  once  cautiously  with  dilute  hydrochloric 
or  nitric  acid,  in  order  to  proceed  with  the  solution  according 
to  192  (not  applicable  in  presence  of  boracic  acid  or  fluorine)  ; 
or  taking  the  fluid  obtained  by  boiling  the  residue  with  water, 
precipitate  the  dissolved .  silica  by  warming  with  ammonium 
carbonate,  and  throw  down  the  last  portion  of  silica  from  the 
filtrate  by  zinc  oxide  dissolved  in  ammonia  (189j. 

The  silicic  acid  is  then  found  partly  in  the  residue  left 
undissolved  by  water,  partly  in  the  precipitate  produced  by 
ammonium  carbonate,  and  partly  in  the  precipitate  produced 
by  the  zinc  solution.  Separate  it  according  to  §  140,  II.,  a. 
Boracic  acid  and  fluorine  will  be  found  entirely  in  the  last 
alkaline  filtrate  (189).  Regarding  phosphoric  acid  see  191. 
Sulphuric  acid  passes  for  the  most  part  into  the  last  alkaline 
filtrate,  yet  it  is  well  also  to  examine  the  acid  filtrates  from 
the  silica. 

6.  CARBONIC  Aero  FROM  ALL  OTHER  ACIDS. 

When  carbonates  are  heated  with  stronger  acids,  the  car-  194 
*  Zeitschr.  f.  anal.  Chem.  8,  70. 


588  SEPARATION.  [§  167. 

bonic  acid  is  expelled  ;  the  presence  of  carbonates,  therefore, 
does  not  interfere  with  the  estimation  of  most  other  acids. 
And  as,  on  the  other  hand,  the  carbonic  acid  is  determined  by 
the  -loss  of  weight  or  by  combination  of  the  expelled  gas,  the 
presence  of  salts  of  non-volatile  acids  does  not  interfere  with 
the  determination  of  the  carbonic  acid.  Accordingly,  with 
compounds  containing  carbonates,  sulphates,  phosphates,  &c., 
either  the  carbonic  acid  is  determined  in  one  portion,  and  the 
other  acids  in  another,  or  both  estimations  are  performed  on 
one  portion.  In  the  latter  case  the  process  described  p.  412,  e, 
may  be  used  with  advantage,  the  other  acids  being  determined 
in  the  solution  remaining  in  the  decomposing  flask.  In  pres- 
ence of  fluorides,  one  of  the  weak  non-volatile  acids,  such  as 
tartaric  acid  or  citric  acid,  must  be  employed  to  expel  the 
carbonic  acid  ;  since,  were  sulphuric  or  hydrochloric  acid  used, 
part  of  the  liberated  hydrofluoric  acid  would  escape  with  the 
carbonic  acid.  If,  as  will  occasionally  happen  in  an  analysis, 
a  mixed  precipitate  of  calcium  fluoride  and  calcium  carbonate 
is  thrown  down  from  a  solution,  the  two  salts  may  be  separated 
by  evaporating  with  acetic  acid  to  dry  ness,  and  extracting  the 
residue  with  water  ;  the  calcium  acetate  formed  from  the  car- 
bonate is  dissolved  the  calcium  fluoride  is  left  behind. 


Second  Group. 

CHLORINE BROMINE IODINE CYANOGEN SULPHUR. 

I.  SEPARATION  OF  THE  ACIDS  OF  THE  SECOND  GROUP  FROM  THOSE 

OF  THE  FIRST. 

§167. 

a.  All  the  Acids  of  the  Second  Group  from  those 
of  the  First. 

Mix  the  dilute  solution  with  nitric  acid,  add  silver  nitrate  195 
in  excess,  and  filter  off  the  insoluble  chloride,  bromide,  iodide, 
&c.,  of  silver.  The  filtrate  contains  the  whole  of  the  acids  of 
the  first  group,  the  silver  salts  of  these  acids  being  soluble  in 
water  or  nitric  acid.  Carbonic  acid  must,  under  all  circum- 
stances, be  determined  in  a  separate  portion  (§  139,  e). 


§  167.]  ACIDS    OF   GROUP   II.  589 

b.  Some  of  the  Acids  of  the  Second  Group  from 
Acids  of  the  First  Group. 

As  it  is  often  inconvenient  for  the  further  separation  of  196 
the  acids  of  the  second  group  to  have  them  all  in  the  form  of 
insoluble  silver  compounds,  the  analysis  is  sometimes  effected 
by  separating  first  the  acid  of  the  first  group,  then  that  of  the 
second.  If  the  quantity  of  substance  is  large  enough,  the 
most  convenient  way  generally  is  to  determine  the  several 
acids,  e.g.,  sulphuric  acid,  phosphoric  acid,  chlorine,  sulphur, 
<fcc.,  in  separate  portions. 

Of  the  infinite  number  of  combinations  that  may  present 
themselves  we  will  here  consider  only  the  most  important. 

1.  SULPHURIC  ACID  may  be  readily  separated  from  chlorine,  197 
bromine,  iodine,  and  cyanogen,  by  precipitation  with  a  barium 
salt.     If  the  acids  of  the  second  group  are  to  be  determined 

in  the  same  portion,  barium  nitrate  or  acetate  is  used  instead 
of  barium  chloride.  In  presence  of  hydrogen  sulphide,  sul- 
phuric acid  cannot  be  determined  in  this  way,  as  part  of  the 
hydrogen  sulphide  would  be  converted  into  sulphuric  acid  by 
the  oxygen  of  the  air.  The  error  thus  introduced  into  the 
process  may  be  very  considerable  (FRESENIUS*)  The  hydrogen 
sulphide  must,  therefore,  first  be  removed  by  cupric  chloride, 
and  the  sulphuric  acid  determined  in  the  filtrate ;  or,  the 
hydrogen  sulphide  must  be  completely  oxidized  into  sulphuric 
acid  by  chlorine  or  bromine,  and  a  corresponding  deduction 
afterwards  made  in  calculating  the  quantity  of  the  sulphuric 
acid.  In  other  cases  it  is  well  to  expel  the  hydrogen  sulphide 
according  to  p.  468.  §  148,  <?,  by  heating  with  hydrochloric 
acid,  and  to  estimate  the  sulphuric  acid  in  the  residual  fluid. 

2.  PHOSPHORIC  ACID  may  be  precipitated  by  ammonium  198 
magnesium    nitrate,   after   addition   of   ammonium    nitrate; 
OXALIC  ACID  by  calcium  nitrate ;  chlorine,  bromine,  iodine,  &c.. 

are  determined  in  the  filtrate. 

3.  CHLORINE  IN  SILICATES. 

a.  If  the  silicates  dissolve  in  dilute  nitric  acid,  precipitate  199 
the  highly  dilute  solution  with  silver  nitrate,  without  applying 
heat,  remove  the  excess  of  silver  from  the  filtrate  by  dilute 

*  Journ.  f.  prakt.  Chem.  70,  9. 


590  SEPAKATION.  [§  167. 

hydrochloric  acid,  still  without  applying  heat,  and  then  sepa- 
rate the  silicic  acid  in  the  usual  way. 

&.  If  the  silicate  becomes  gelatinous  upon  decomposition, 
with  nitric  acid,  dilute,  allow  to  deposit,  filter,  wash  the  sepa- 
rated silicic  acid,  and  treat  the  filtrate  as  in  a. 

In  the  processes  a  and  b  the  silver  chloride  may  contain 
silica.  Reduce  the  weighed  silver  salt  by  hydrogen  and  treat 
with  nitric  acid,  the  silica  will  remain  behind. 

c.  If  nitric  acid  fails  to  decompose  the  silicates,  mix  the 
substance  with  sodium  and  potassium  carbonates,  moisten  the 
mass  with  water,  dry  in  the  crucible,  fuse,  boil  with  water, 
remove  the  dissolved  silicic  acid  by  ammonium  carbonate  and 
zinc  oxide  dissolved  in  ammonia  (189),  and  then  precipitate, 
after  addition  of  nitric  acid,  with  silver  nitrate. 

4.  CHLORIDES  IN  PRESENCE  OF  FLUORIDES. 

If  the  substance  is  soluble  in  water,  the  separation  may  be  200 
effected  as  directed  195  ;  but  it  is  more  convenient  to  precipi- 
tate the  fluorine  with  calcium  nitrate,  and  the  chlorine  in  the 
filtrate  with  silver  nitrate.     Insoluble  compounds  are  fused 
with  sodium  carbonate  and  silicic  acid,  and  treated  as  in  201. 

5.  CHLORIDES  IN  PRESENCE  OF  FLUORIDES  IN  SILICATES. 
Proceed  as  directed  189.      Saturate   the  alkaline  filtrate  201 

nearly  with  nitric  acid,  precipitate  with  calcium  nitrate,  sepa- 
rate the  calcium  fluoride  and  carbonate  as  directed  in  194,  and 
precipitate  the  chlorine  in  the  filtrate  by  silver  nitrate. 

6.  SULPHIDES  IN  SILICATES. 

If  the  substance  is  decomposable  by  acids,  reduce  it  to  the  202 
very  finest  powder,  and  treat  with  fuming  nitric  acid  free  from 
sulphuric  acid  (§  148,  II.,  2,  a),  or  with  rather  dilute  nitric 
acid  in  sealed  tubes  at  120—150°  (CARIUS).  When  the  sul- 
phur is  completely  oxidized,  rinse  the  contents  of  the  flask  or 
tube  into  a  dish,  evaporate  on  the  water  bath,  treat  with  hydro- 
chloric or  nitric  acid,  dilute,  filter  off  the  silica,  and  determine 
in  the  filtrate  the  sulphuric  acid  formed.  If,  on  the  contrary, 
the  substance  is  not  decomposable  by  acids,  fuse  with  4  parts 
of  sodium  carbonate  and  1  part  of  potassium  nitrate,  boil  the 
fused  mass  with  water,  filter,  remove  the  dissolved  silicic  acid 


§  168.]  ACIDS   OF   GROUP  591 

from  the  filtrate  by  acidifying  with  hydrochloric  or  nitric  acid 
and  evaporating,  and  proceed  as  above  directed. 

7.  SULPHIDES  IN  PRESENCE  OF  CARBONATES. 

If  you  have  to  estimate  sulphur  in  sulphides,  which  can  20$ 
easily  be  decomposed  by  acids  (e.g.,  calcium  sulphide),  in  pres- 
ence of  carbonates,  decompose  the  substance  by  heating  with 
hydrochloric  acid,  dry  the  evolved  mixture  of  hydrogen  sul- 
phide and  carbonic  acid,  take  up  the  hydrogen  sulphide  by 
tubes  filled  with  pumice  prepared  with  cupric  sulphate  (p. 
±10),  and  the  carbonic  acid  by  soda-lime  tubes  (p.  631). 

Supplement. 

ANALYSIS  OF  COMPOUNDS,  CONTAINING  ALKALI  SULPHIDES,  CARBON- 
ATES, SULPHATES,  AND  THIOSULPHATES. 

§168. 

The  following  method  was  first  employed  by  G.  WERTHER*  204 
in  the  examination  of  gunpowder  residues.     N.  FEDOROwf  has 
shown  that  the  original  process  included  an  error,  which  has 
been  put  right  in  the  method  described  below. 

Put  the  substance  into  a  flask,  add  water,  in  which  a  suf- 
ficient quantity  of  cadmium  carbonate^  is  suspended ;  cork, 
and  shake  the  vessel  well.  The  alkali  sulphide  decomposes 
completely  with  the  cadmium  carbonate.  Filter  the  yellowish 
precipitate  off,  and  treat  it  with  dilute  acetic  acid  (not  with 
hydrochloric  acid) ;  the  cadmium  carbonate  dissolves,  the 
cadmium  sulphide  is  left  undissolved.  Oxidize  the  latter  with 
potassium  chlorate  and  nitric  acid  (p.  466),  or  with  bromine 
(p.  467),  and  precipitate  with  barium  chloride  the  sulphuric 
acid  formed  from  the  sulphide. 

Heat  the  fluid  filtered  from  the  yellow  precipitate,  and 
mix  with  solution  of  neutral  silver  nitrate.  The  precipitate 
consists  of  silver  carbonate  and  silver  sulphide  (K2S2O,-(- 
2AgXO3+H2O=K2SO4+Ag2S+2HlSTO3).  Filter  it  off,  and 
wash  with  carbonic  acid  water,  then  remove  the  silver 

*  Journ.  f.  prakt.  Chem.  55,  22.  f  Zeitschr.  f.  anal.  Chem.  9,  127. 

\  To  obtain  the  cadmium  carbonate  free  from  alkali,  ammonium  carbonate 
must  be  used  as  precipitant. 


592  SEPARATION.  [§  169. 

carbonate  by  ammonia  and  precipitate  the  silver  from  the 
am  moniacal  solution  by  acidifying  with  nitric  acid  and  adding 
sodium  chloride.  2  mol.  silver  chloride  so  obtained  corre- 
spond to  1  mol.  carbonate.*  Dissolve  the  silver  sulphide  in 
dilute  boiling  nitric  acid,  determine  the  silver  in  the  solution 
as  silver  chloride,  and  calculate  from  the  result  the  quantity 
of  the  thiosulphuric  acid;  1  mol.  AgCl  corresponds  to  1  at. 
sulphur  in  thiosulphuric  acid,  or  2  AgCl  correspond  to  KJSaO3. 
From  the  fluid  filtered  from  the  silver  sulphide  and 
carbonate  remove  first  the  excess  of  silver  by  means  of 
hydrochloric  acid,  and  then  precipitate  the  sulphuric  acid  by 
a  barium  salt.  From  the  sulphuric  acid  found  you  have,  of 
course,  to  deduct  the  quantity  of  that  acid  resulting  from  the 
decomposition  of  the  thiosulphuric  acid,  and  accordingly  for  1 
part  of  silver  chloride  formed  from  the  sulphide,  *2T9  parts  of 
sulphuric  anhydride  (SO3).  The  difference  gives  the  amount 
of  sulphuric  acid  originally  present  in  the  analyzed  compound. 
By  way  of  control,  you  may  determine,  in  the  fluid  filtered 
from  the  barium  sulphate,  the  alkali  as  sulphate  (§  97  or  §  98). 

II.  SEPARATION  OF  THE  ACIDS  OF  THE  SECOND  GROUP  FROM 

EACH  OTHER. 

§169. 

1.  CHLORINE  FROM  BROMINE. 

All  the  methods  of  direct  analysis  hitherto  proposed  to 
effect  the  separation  of  chlorine  from  bromine  are  defective. 
The  bromine  is  therefore  always  determined  in  a  more  indi- 
rect way. 

a.  Precipitate   with  silver  nitrate,  wash  the  precipitate,  205 
wash  it  from  the  filter  into  a  porcelain  dish,  extract  the  filter 
with  hot  ammonia,  evaporate  the  ammonia  in  a  weighed  porce- 
lain crucible,  add  the  principal  quantity  of  the  precipitate, 
dry,  fuse,  and  weigh.     Transfer  an  aliquot  part  of  the  mixed 

*  A  quantity  equivalent  to  the  sulphur  found  existing  as  sulphide  has  to  be 
deducted  from  this  (K2S-fCdCO3=CdS-f  K2CO3).  On  the  other  hand,  a  quan- 
tity equivalent  to  the  sulphide  of  silver  precipitated  by  the  thiosulphate  must  be 
added,  for  each  mol.  of  sulphide  of  silver  from  the  thiosulphate  gives  2  mol. 
HNO3,  which  decomposes  1  mol.  carbonate  of  silver.  This  correction  was 
overlooked  by  WERTHER. 


§  169.]  ACIDS    OF   GROUP   II.  593 

silver  chloride  and  bromide  to  a  light  weighed  bulb-tube  of 
hard  glass,*  fuse  in  the  bulb,  let  the  mass  cool,  and  weigh. 
This  operation  gives  both  the  total  weight  of  the  tube  with 
its  contents,  and  the  weight  of  the  portion  of  mixed  silver 
chloride  and  bromide  in  the  bulb.  The  greatest  accuracy  in 
the  several  weighings  is  indispensable.  Now  transmit  through 
the  tube  a  slow  stream  of  dry  pure  chlorine  gas,  heat  the  con- 
tents of  the  bulb  to  fusion,  and  shake  the  fused  mass  occasion- 
ally about  in  the  bulb.  After  the  lapse  of  about  20  minutes, 
take  off  the  tube,  allow  it  to  cool,  hold  it  in  an  oblique  posi- 
tion, that  the  chlorine  gas  may  be  replaced  by  atmospheric 
air,  and  then  weigh.  Heat  once  more  for  about  10  minutes  in 
a  stream  of  chlorine  gas,  and  weigh  again.  If  the  two  last 
weighings  agree,  the  experiment  is  terminated ;  if  not,  the 
operation  must  be  repeated  once  more.  The  loss  of  weight 
suffered,  multiplied  by  4'22297  (which  may  be  taken  as  4-223), 
gives  the  quantity  of  the  silver  bromide  decomposed  by  the 
chlorine.  For  the  proof  of  this  rule,  see  "  Calculation  of 
Analyses." 

This  method  gives  very  accurate  results,  if  the  proportion 
of  bromine  present  is  not  too  small;  but  most  uncertain 
results  in  cases  where  mere  traces  of  bromine  have  to  be 
determined  in  presence  of  large  quantities  of  chlorides,  as,  for 
instance,  in  salt-springs.  To  render  the  method  available  in 
such  cases,  the  great  point  is  to  produce  a  silver  compound 
containing  all  the  bromine,  and  only  a  small  part  of*  the 
chlorine.  This  end  may  be  attained  in  several  ways.  In 
these  processes  the  quantity  of  chlorine  is  found  by  completely 
precipitating  a  separate  portion  with  silver  solution,  and 
deducting  the  silver  bromide  found  from  the  weight  of  the 
precipitate. 

of.  Mix  the  solution  with  sodium  carbonate  in  excess  (if  a 
precipitate  is  formed,  do  not  filter),  evaporate  to  dryness,  ' 
powder  the  residue,  extract  with  hot  absolute  alcohol ;  the 
solution  contains  the  whole  of  the  alkali  bromide,  and  only  a 
small  portion  of  the  alkali  chloride ;  add  a  drop  of  soda  solu- 
tion, and  evaporate,  dissolve  the  residue  in  water,  acidify  with 
nitric  acid,  and  precipitate  with  silver  solution. 

*  The  best  way  of  effecting  the  removal  of  the  fused  mass  from  the  crucible 
is  to  fuse  again,  and  then  pour  out. 


594  SEPARATION.  [§  169. 

ft.  FEHLING'S  method.*  Mix  the  solution  cold  with  a  206 
quantity  of  solution  of  silver  nitrate  not  nearly  sufficient  to 
effect  complete  precipitation,  shaking  the  mixture  vigorously, 
and  leave  the  precipitate  for  some  time  in  the  fluid,  with 
repeated  shaking.  If  the  amount  of  the  precipitate  produced 
corresponds  at  all  to  the  quantity  of  bromine  present,  the 
whple  of  the  latter  substance  is  obtained  in  the  precipitate. 

FEHLING  gives  the  following  rule  : 

If  the  fluid  contains  1  bromine  to  1000  chlorine  use  J  or  -J- 
the  quantity  of  silver  nitrate  that  would  be  required  to  effect 
complete  precipitation ;  if  the  fluid  contains  10,000  times  as 
much  chlorine  as  bromine,  use  -^ ;  if  50,000,  use  ^ ;  if 
100,000,  use  -g-V 

Wash  the  mixed  precipitate  of  silver  chloride  and  bromide 
thoroughly,  dry,  ignite,  weigh,  and  treat  with  chlorine  as 
above. 

y.  MARCHANDf  has  slightly  modified  FEHLING'S  method.  207 
He  reduces  with  zinc  the  mixed  precipitate  of  silver  chloride 
and  bromide  obtained  by  FEHLING'S  fractional  precipitation, 
decomposes  the  solution  of  zinc  chloride  and  bromide  with 
sodium  carbonate,  evaporates  to  dryness,  and  extracts  the  resi- 
due with  absolute  alcohol,  which  dissolves  all  the  sodium 
bromide  with  only  a  little  of  the  sodium  chloride ;  he  then 
evaporates  the  solution  to  dryness,  takes  up  the  residue  with 
water,  precipitates  again  with  silver  nitrate,  and  subjects  a 
part  of  the  weighed  precipitate  to  the  treatment  with  chlorine. 

8.  If  a  fluid  containing  chlorides  in  presence  of  some 
bromide  is  heated  in  a  retort  with  hydrochloric  acid  and 
manganese  dioxide,  the  whole  of  the  bromine  passes  over  before 
any  of  the  chlorine.  Under  this  circumstance  MOHR^:  bases 
the  following  method  for  effecting  the  concentration  of 
bromine : — Distil  as  stated,  and  conduct  the  vapors,  through  a 
doubly  bent  tube,  into  a  wide  WOULF'S  bottle,  which  contains 
some  strong  ammonia.  Dense  fumes  form  in  the  bottle,  fill- 
ing it  gradually.  Conduct  the  excess  of  vapors  from  the  first 
into  a  second  bottle,  with  narrow  neck,  containing  ammoniated 
water.  Both  bottles  must  be  sufficiently  large  to  allow  no 
vapors  to  escape.  When  the  whole  of  the  bromine  is  evolved, 

*  Journ,  f.  prakt.  Chem.  45,  269. 

f  Ib.  47,  363.  \  Anna],  d.  Chem.  u.  Pharm.  93,  80. 


£  169.]  ACIDS    OF    GROUP    II.  595 

which  may  be  distinctly  seen  by  the  color  of  the  space  above 
the  liquid  in  the  retort  and  tubes,  raise  the  cork  of  the  flask  to 
prevent  the  receding  of  ammonium  bromide  fumes.  Let  the 
apparatus  cool,  and  unite  the  contents  of  the  two  bottles ;  the 
fluid  contains  the  whole  of  the  bromine,  with  a  relatively  small 
portion  of  the  chlorine. 

I.  Determine  in  a  portion  of  the  solution  the  chlorine  208 
+  bromine  (by  precipitating  with  silver),  either  gravimetrically 
or  volumetrically ;  in  another  portion  the  bromine,  either  by 
the  colorimetric  method  (§  143,  I.,  &,  ft)  or  volumetrically 
(§  143, 1.,  J,  a).  Calculate  the  chlorine  from  the  difference. 
The  method  is  very  suitable  for  an  expeditious  analysis  of 
mother-liquors. 

'2.  CHLORINE  FROM  IODINE. 

a.  Mix  the  solution  with  palladious  nitrate,  and  determine  209 
the  precipitated  palladious  iodide  as  directed  §  145,  I.,  #,  ft. 
Conduct  hydrogen  sulphide  into  the  filtrate  to  remove  excess 
of  the  palladium,  destroy  the  excess  of  hydrogen  sulphide  by 
solution  of  ferric  sulphate,  and  precipitate  the  chlorine  finally 
with  solution  of  silver.  It  is  generally  found  more  simple 
and  convenient  to  precipitate  from  one  portion  the  iodine,  by 
means  of  palladious  chloride,  as  directed  §  145,  I.,  #,  /?,  from 
another  portion  the  chlorine  and  iodine  jointly  with  silver 
nitrate,  and  to  calculate  the  chlorine  from  the  difference.  If 
you  have  no  solution  of  palladious  nitrate  ready,  and  the 
chlorine  and  iodine  must  be  determined  in  one  portion  of  the 
solution  under  examination,  add  a  measured  quantity  of  a 
solution  of  palladious  chloride,  determine  the  amount  of  chlo- 
rine in  this  in  another  exactly  equal  portion  of  the  same  solu- 
tion, and  deduct  it.  The  results  are  accurate.  In  the  case  of 
fluids  containing  a  large  proportion  of  alkali  chlorides  to  a  small 
quantity  of  iodide — and  such  cases  often  occur — the  iodide  is 
concentrated  by  adding  sodium  carbonate  to  the  fluid,  evapo- 
rating to  dryness,  extracting  the  residue  with  hot  alcohol, 
evaporating  the  alcoholic  solution  with  addition  of  a  drop  of 
solution  of  soda,  and  taking  the  residue  up  with  water. 

1}.  Proceed  exactly  as  for  the  indirect  determination  •  of  210 
bromine  in  presence  of   chlorine  (205).     The  greatest  care 
must  be  taken  that  as  little  as  possible  of  the  mixed  silver  ehlo- 


596  SEPARATION.  [§  169. 

ride  and  iodide  adheres  to  the  filter,  for  silver  iodide  dissolves 
onlv  very  slightly  in  ammonia.  Any  particles  of  silver  iodide 
remaining  attached  to  the  filter  may  be  saved  by  incinerating 
the  filter  and  evaporating  the  ash  with  a  drop  of  nitric  acid 
and  a  drop  of  hydriodic  acid.  The  loss  of  weight  suffered  by 
the  silver  precipitate  on  fusion  in  chlorine  multiplied  by  2'569 
gives  the  amount  of  silver  iodide  present.  This  method  gives 
still  better  results  than  in  the  separation  of  bromine  from 
chlorine,  inasmuch  as  the  difference  between  the  atomic 
weights  of  iodine  and  chlorine  is  far  greater  than  the  differ- 
ence between  those  of  bromine  and  chlorine.  Regarding  the 
concentration  of  the  iodide,  if  necessary,  see  209. 

c.  Liberate  the  iodine  by  nitrous  acid,  take  it  up  with  car-  211 
bon  disulphide,  wash  the  latter,  and  then  estimate  the  iodine 

in  it  by  sodium  thiosulphate  (p.  MO,  /?). 

In  this  process  the  chlorine  is  determined,  either  in  the 
fluid  separated  from  the  violet  carbon  disulphide,  or  with 
greater  accuracy  by  precipitating  the  chlorine  -f-  iodine  in 
a  second  portion  with  silver,  and  deducting  the  weight  of 
silver  iodide  corresponding  to  the  iodine  already  found  from 
the  weight  of  the  precipitate.  A  good  and  approved  method. 

If  the  quantity  of  iodine  is  small,  the  following  method 
may  also  be  used  with  advantage  for  estimating  it : 

The  carbon  disulphide  should  be  thoroughly  washed,  cov- 
ered with  a  layer  of  water,  and  in  a  stoppered  bottle.  Add 
drop  by  drop,  with  shaking,  dilute  chlorine  water  (of  unknown 
strength),  till  the  coloration  has  just  vanished,  and  all  the 
iodine  is  consequently  converted  into  IC15.  Separate  the  solu- 
tion from  the  disulphide,  add  potassium  iodide  solution  in  suf- 
ficient excess,  and  determine  the  free  iodine  after  §  146.  Six 
parts  of  the  iodine  found  correspond  to  1  part  originally  pres- 
ent. If  the  analyst  would  avoid  the  trouble  of  pouring  off  the 
fluid  from  the  disulphide,  and  of  washing  the  latter,  he  may 
transfer  the  mixture,  after  the  addition  of  chlorine  to  decolor- 
ation, to  a  somewhat  narrow  measuring  cylinder,  note  the  vol- 
ume occupied  by  the  iodine  pentachloride  solution,  take  out  a 
portion  with  a  pipette,  and  proceed  as  above  directed. 

d.  For  technical  purposes  the  following  method  is  also  212 
suitable.     It  was  recommended  by  WALLACE  and  LAMONT*  for 

*  Chem.  Gaz.  1859,  137. 


§  169.]  ACIDS   OF  GROUP  II.  597 

the  estimation  of  iodine  in  kelp.  The  kelp-lie  is  nearly  neu- 
tralized with  nitric  acid,  evaporated  to  dryness,  and  the  residue 
fused  in  a  platinum  vessel  to  oxidation  of  all  the  sulphides. 
Treat  with  water,  filter,  add  silver  nitrate  till  the  precipitate 
appears  perfectly  white,  wash,  digest  with  strong  ammonia,  and 
weigh  the  residual  silver  iodide.  Finally,  add  to  the  weight 
of  the  latter  the  amount  which  passes  into  solution  in  the 
ammonia ;  it  is  ^^^  of  the  aqueous  ammonia  (sp.  gr.  -89) 
used. 

3.  CHLOKINE,  BROMINE,  AND  IODINE  FROM  EACH  OTIIKR. 

a.  The  three  acid  radicals  are  determined  jointly  in  a  por-  213 
tion  of  the  fluid  by  precipitating  with  solution  of  silver 
nitrate  (§  141,  I.,  a  or  &,  a).  To  determine  the  iodine,  another 
portion  is  precipitated  with  palladious  chloride  in  the  least  pos- 
sible excess  (§  145,  I.,  a,  ft).  The  fluid  filtered  from  the  pre- 
cipitate is  freed  from  palladium  by  hydrogen  sulphide  and  the 
excess  of  the  latter  removed  by  means  of  ferric  sulphate  ;  the 
chlorine  and  bromine  are  then  precipitated  jointly  either  com- 
pletely or  partially  with  silver  nitrate,  and  the  bromine  deter- 
mined as  directed  205. 

If  the  compound  contains  a  large  proportion  of  chlorine  to 
a  small  proportion  of  bromine,  the  iodine  may  be  precipitated 
also  by  palladious  nitrate,  as  there  is  no  danger,  in  that  case, 
of  palladious  bromide  being  coprecipitated.  The  filtrate  is 
treated  as  above. 

These  methods  give  accurate  results ;  but  they  are  appli- 
cable only  if  the  quantity  of  iodide  present  is  somewhat  con- 
siderable. 

1).  Mix  the  neutral  dilute  and  cold  solution  containing  alkali  214 
iodide  with  alkali  chloride  or  alkaki  bromide,  or  both,  with  a 
saturated  neutral  solution  of  thallium  nitrate,  stirring  well  till, 
on  repeated  trial,  you  obtain  a  transient  white  precipitate — 
the  first  and  permanent  precipitate  being  yellow.  It  is  best  to 
have  the  thallium  solution  in  a  burette,  so  that  yon  can  easily 
add  it  by  drops.  If  the  white  precipitate  of  thallium  chloride 
or  bromide  does  not  at  once  disappear  on  stirring,  add  more 
water,  but  not  an  unnecessary  quantity,  or  some  of  the  thal- 
lium iodide  will  remain  in  solution. 

Allow  to  stand  eight  or  twelve  hours  in  a  cold  place,  pour 
off  the  clear  fluid  through  a  weighed  filter  dried  at  100°,  wash 


598  SEPARATION.  [§  169. 

the  filter  a  little  so  that  no  more  water  than  necessary  may 
pass  through  the  precipitate,  turn  the  precipitate  on  to  the 
filter,  wash  with  as  little  water  as  you  can,  dry  at  100°,  and 
weigh.  Precipitate  the  chlorine  and  bromine  in  the  filtrate 
hy  silver  solution.  If  they  are  both  present,  the  mixed  silver 
precipitate  is  to  be  treated  according  to  205.  Results  quite 
satisfactory  (HUBNER  and  SPEZIA,*  and  HUBNER  and  FRE- 

RICHsf). 

c.  Remove  the  iodine  from  the  solution  by  carbon  disul-  215 
phide  or  chloroform,  as  in  211.     In  the  fluid  separated  from 

the  iodized  carbon  disul  phide  determine  the  chlorine  and  bro- 
mine as  directed  205,  and  in  the  iodized  carbon  disulphide,  the 
iodine  as  directed  §  145,  I.,  &,  ft.  This  method  is  particularly 
recommended  for  the  separation  of  small  quantities  of  iodine, 
and  in  this  respect  is  supplementary  to  213. 

d.  Determine   in   a  portion  of  the  compound   the  chlo-  216 
rine,  bromine,  and  iodine  jointly  by  adding  a  known  quantity 

of  standard  silver  solution  in  slight  excess,  filtering  and  deter- 
mining the  small  excess  of  silver  in  the  filtrate  by  iodide  of 
starch  (p.  295).  The  precipitate  is  weighed,  compare  210. 
We  now  know  the  tatal  of  the  chloride,  bromide,  and  iodide 
of  silver  and  also  the  silver  therein  contained. 
.  Determine  the  iodine  separately  as  in  215,  calculate  the 
quantity  of  silver  iodide  and  of  silver  corresponding  to  the 
amount  found,  deduct  the  calculated  amount  of  silver  iodide 
from  the  mixed  iodide,  chloride,  and  bromide  of  silver,  that  of 
the  silver  from  the  known  quantity  of  the  metal  contained  in 
the  mixed  compound ;  the  remainders  are  respectively  the 
joint  amount  of  chloride  and  bromide  of  silver,  and  the  quan- 
tity of  the  metal  contained  therein  ;  these  are  the  data  for 
calculating  the  chlorine  and  bromine. 

4.  ANALYSIS  OF  IODINE  CONTAINING  CHLORINE. 

a.  Dissolve  a  weighed  quantitity  of  the  dried  iodine  in  217 
cold  sulphurous  acid,  precipitate  with  silver  nitrate,  digest  the 
precipitate  with  nitric  acid,  to  remove  the  silver  sulphite 
which  may  have  coprecipitated,  and  weigh.      The  calculation 
of  the  iodine  and  chlorine  is  made  by  the  following  equations, 
in  which  A  represents  the  quantity  of  iodine  analyzed,  x  the 

*  Zeitschr.  f.  anal.  Chem.  11,  397.  f  Ib.  11,  400. 


§  169.]  ACIDS   OF   GROUP   II.  599 

iodine  contained  in  it,  y  the  chlorine  contained  in  it,  and  B 
the  amount  of  silver  chloride  and  iodide  obtained  : 


#  +  y  — 

and 


as 


and 


we  have 

_£  -I-S51A 
2-1929 

b.  If  you  have  free  iodine  and  free  chlorine  in  solution,  deter-  218 
mine  in  one  portion,  after  heating  with  sulphurous  acid,  the 
iodine  as  palladium  iodide  (§  145,  I.,  a,  /?),  and  treat  another 
portion  as  directed  §  146.  Deduct  from  the  apparent  amount 
of  iodine  found  by  the  latter  process,  the  actual  quantity  calcu- 
lated from  the  palladium  iodide  :  the  difference  expresses  the 
amount  of  iodine  equivalent  to  the  chlorine  contained  in  the 
substance. 

5.  ANALYSIS  OF  BROMINE  CONIAINING  CHLORINE. 
a.  Proceed  exactly  as  in  217,  weighing  the  bromine  in  a  219 
small  glass  bulb.     Taking  A  to  be  equal  to  the  analyzed  bro- 
mine, B  to  the  silver  bromide  and  chloride  obtained,  x  to  the 
bromine  contained  in  A,  y  to  the  chlorine  contained  in  A,  the 
calculation  is  made  by  the  following  equations  : 

x-\-y  =  A 
and 

_B  —  2-34997  A 
1-69374 

5.  Mix  the  weighed  anhydrous  bromine  with  solution  of  220 
iodide  of  potassium  in  excess,  and  determine  the  separated 
iodine  as  directed  §  146. 


600  SEPARATION.  [§  169. 

From  these  data,  the  respective  quantities  of  bromine  and 
chlorine  are  calculated  by  the  following  equations.  Let  A 
represent  the  weighed  bromine,  i  the  iodine  found,  y  the 
chlorine  contained  in  A,  so  the  bromine  contained  in  J.,  then 


=  A 

_i  —  1-5866  A 

1-9907 

BUNSEN,  the  originator  of  methods  4:  and  5,  has  experi- 
mentally proved  their  accuracy.* 

6.   CYANOGEN  FROM  CHLORINE,  BROMINE,  OR   IODINE. 

a.  Precipitate  with  solution  of  silver,  collect  the  precipi-  221 
tate  upon  a  weighed  filter,  and  dry  in  the  water-bath  until  the 
weight  remains  constant  ;  then  determine  the  cyanogen  by  the 
method  of  organic  analysis  ;  the  quantity  of  the  chlorine,  bro- 
mine, or  iodine  is  found  by  difference. 

b.  Precipitate  with  solution  of  silver  as  in  a,  dry  the  pre-  222 
cipitate  at  100°  and  weigh.     Heat  the  precipitate,  or  an  ali- 
quot part  of  it,  in  a  porcelain  crucible,  with  cautious  agitation 

of  the  contents,  to  complete  fusion  ;  add  dilute  sulphuric  acid 
to  the  fused  mass,  then  reduce  by  zinc,  filter  the  solution  from 
the  metallic  silver  and  silver  paracyanide,  and  determine  the 
chlorine,  iodine,  or  bromine  in  the  filtrate,  in  the  usual  way 
by  silver.  The  silver  cyanide  is  the  difference.  NEUBAUER 
and  KERNERf  obtained  very  satisfactory  results  by  this 
method. 

c.  Precipitate  with  solution  of  silver  as  in  a,  weigh  the  pre-  223 
cipitate  and  heat  it,  or  an  aliquot  part,  with  nitric  acid  of  1*2 

sp.  gr.  in  a  sealed  tube  at  100°  for  several  hours,  or  at  150° 
for  one  hour.  The  silver  cyanide  is  completely  decomposed, 
while  the  chloride,  bromide,  or  iodide  are  unaffected.  Filter 
the  contents  of  the  tube,  wash  the  precipitate  and  weigh  it, 
the  loss  indicates  the  amount  of  silver  cyanide  (K.  KRAUT;):). 

d.  Determine  the  radicals  jointly  in  a  portion  by  precipi-  224 
tating  with  solution  of  silver,  and  the  cyanogen  in  another 
portion,  in  the  volumetric  way  (§  147,  L,  b). 

*  Annal.  d.  Chem.  u.  Pharm.  86,  274,  276.  f  Ib.  101,  344. 

\  Zeitschr.  f.  anal.  Chem.  2,  243. 


ACIDS    OF   GROUP  II.  601 

T.  FERRO-  OR  FERRICYANOUKX  FROM    HYDROCHLORIC 
ACID. 

To  analyze  say  potassium  f erro-  or  f erricyanide,  mixed  with  225 
an  alkali  chloride,  determine  in  one  portion  the  ferro-  or  ferri- 
cyanogen  as  directed  §  147,  II.,  g ;  acidify  another  portion 
with  nitric  acid,  precipitate  with  solution  of  silver,  wash  the 
precipitate,  fuse  with  4  parts  of  sodium  carbonate  and  1  part 
of  potassium  nitrate,  extract  the  fused  mass  with  water,  and 
determine  the  chlorine  in  the  solution  as  directed  in  §  141. 

8.  SULPHUR  (ix  SULPHIDES)  FROM  CHLORINE. 
The  old  method  of  separating  the  two  radicals  by  means  of  a  226 
metallic  salt  is  liable  to  give  false  results,  as  part  of  the  chlo- 
rine may  fall  down  as  chloride  with  the  sulphide.  We,  there- 
fore, precipitate  both  as  silver  compounds,  dry  the  precipitate 
at  100°,  weigh  it,  and  determine  the  sulphur  in  a  weighed 
portion  ;  or — and  this  is  usually  preferred — determine  in  a 
portion  of  the  solution  the  sulphur  as  directed  §  148,  L,  #,  or 
5,  in  another  portion  the  sulphur  -f-  chlorine  in  form  of  silver 
salts.  If  you  employ  a  solution  of  silver  nitrate  mixed  with 
excess  of  ammonia,  for  the  determination  of  the  sulphur,  you 
may,  after  filtering  off  the  silver  sulphide,  estimate  the  chlo- 
rine directly  as  silver  chloride,  by  adding  nitric  acid,  and,  if 
necessary,  more  neutral  silver  solution.  In  this  case  you  must 
take  care  that  the  silver  sulphide  is  pure ;  should  it  contain 
calcium  carbonate,  which  is  not  unlikely  if  calcium  is  present, 
you  remove  this  with  dilute  acetic  acid.  The  weighed  silver 
sulphide  should  be  reduced  by  hydrogen,  and  then  weighed 
again  by  way  of  control.  To  remove  hydrogen  sulphide  from 
an  acid  solution,  in  order  that  chlorine  may  be  determined  in 
the  latter  by  means  of  silver  nitrate,  H.  ROSE  recommends  to 
add  solution  of  ferric  sulphate,  which  will  effect  the  separa- 
tion of  sulphur  alone ;  the  separated  sulphur  is  allowed  to 
deposit,  and  then  filtered  off. 


602  SEPARATION.  [§  170. 

Third   Group* 

NITRIC    ACID CHLORIC    ACID. 

I.  SEPARATION  OF  THE  ACIDS  OF  THE  THIRD  GROUP  FROM  THOSE 

OF    THE    FIRST   TWO    GROUPS. 

§  1TO. 

a.  If  you  have  a  mixture  of  nitric  acid  or  chloric  acid  with  227 
another  free  acid  in  a  fluid  containing  no  bases,  determine  in 
one  portion  the  joint  amount  of  the  free  acid,  by  the  acidi- 
metric  method  (see  Special  Part),  in  another  portion  the  acid 
mixed  with  the  chloric  or  nitric  acid,  and  calculate  the  amount 
of  either  of  the  latter  from  the  difference. 

Z>.  If  you  have  to  analyze  a  mixture  of  a  nitrate  or  chlorate  228 
with  some  other  salt,  determine  in  one  portion  the  nitric  or 
chloric  acid  volumetrically  (§  149,  II.,  d,  a,  or  /?,  or  II.,  e, 
and  §  150),  or  the  nitric  acid  by  §  149,  II.,  a,  ft ;  and  in 
another  portion  the  other  acid.  I  think  I  need  hardly  remark 
that  no  substances  must  be  present  which  would  interfere  with 
the  application  of  these  methods. 

c.  From  the  chlorides  of  many  metals  whose  carbonates  or  229 
normal  phosphates  are  insoluble,  chlorates  and   nitrates  may 

be  separated  also  by  digesting  the  solution  with  recently  pre- 
cipitated thoroughly  washed  silver  carbonate  or  normal  silver 
phosphate  in  excess,  and  boiling  the  mixture.  In  this  process, 
the  chlorides  react  with  the  carbonate  or  phosphate — silver 
chloride  and  carbonate  or  phosphate  of  the  metal  with  which 
the  chlorine  was  originally  combined  being  formed,  which 
both  separate,  together  with  the  excess  of  the  silver  carbon- 
ate or  phosphate,  whilst  the  chlorates  and  nitrates  remain  in 
solution  (H.  ROSE,  CHENEVIX,  LASSAIGNE*). 

d.  The  estimation  of  an  alkaline  chlorate,  in  presence  of  230 
a  chloride,  may  be  effected  also  by  precipitating  one  portion 

at  once,  and  another  portion  after  gentle  ignition,  with  solu- 
tion of  silver,  and  calculating  the  chloric  acid  from  the  differ- 
ence between  the  two  precipitates. 

e.  Where  you  have  nitrate  of  soda  or  potash  in  presence  of  231 

*  Journ.  de  Pharm.  16,  289;  Pharm.  Centralbl.  1850,  121. 


§  170.]  ACIDS   OF   GROUP   III.  603 

nitrite  or  carbonate,  as  for  instance  in  the  commercial  alkali 
nitrites,  estimate  in  one  portion  the  carbonate  by  standard  acid 
(see  Special  Part),*  in  another  portion  the  nitrous  acid  by 
permanganate  or  chromate  of  potash  (p.  365).  The  nitrate  is 
found  by  difference. 

II.   SEPARATION  OF  THE  Acros  OF  THE  THIRD  GROUP  FROM  EACH 

OTHER. 

We  have  as  yet  no  method  to  effect  the  direct  separation  232 
of  nitric  acid  from  chloric  acid ;  the  only  practicable  way, 
therefore,  is  to  determine  the  two  acids  jointly  in  a  portion  of 
the  compound,  by  the  method  described  for  nitric  acid,  §  149, 
II.,  dj  a,  bearing  in  mind  that  12  atoms  iron  are  converted 
from  a  ferrous  to  a  ferric  salt  by  2  mol.  chloric  acid  (HC1O8) 
or  1  mol.  chloric  anhydride  (C12O5).  In  another  portion  esti- 
mate the  chloric  acid,  by  adding  sodium  carbonate  in  excess, 
evaporating  to  dryness,  fusing  the  residue  until  the  chlorate 
is  completely  converted  into  chloride,  and  then  determining 
the  chlorine  in  the  latter,  taking  care  that  the  silver  chloride 
contains  no  difficultly  soluble  nitrite.  2  mol.  silver  chloride 
produced  from  this  corresponds  to  2HC1O3  or  C12O6,  provided 
there  was  no  chloride  originally  present. 

*The  alkali  nitrites  have  no  alkaline  reaction. 


SECTION"  VI. 

OKGANIC   ANALYSIS. 

§171. 

ORGANIC  compounds  contain  comparatively  only  few  of  the  ele- 
ments. A  small  number  of  them  consist  simply  of  2  elements,  viz., 

C  and  H ; 
the  greater  number  contain  3  elements,  viz.,  as  a  rule, 

C,  H,  and  O  ; 

most  of  the  rest  4  elements,  viz.,  generally, 

C,  H,  O,  and  N ; 
a  small  number  5  elements,  viz., 

C,  H,  O,  N,  and  S ; 
and  a  few,  6  elements,  viz., 

C,  H,  O,  N,  S,  and  P. 

This  applies  to  all  the  natural  organic  compounds  which  have 
as  yet  come  under  our  notice.  But  we  may  artificially  prepare 
organic  compounds  containing  other  elements  besides  those  enu- 
merated ;  thus  we  know  many  organic  substances,  which  contain 
chlorine,  iodine,  or  bromine ;  others  which  contain  arsenic,  anti- 
mony, tin,  zinc,  platinum,  iron,  cobalt,  etc.;  and  it  is  quite  impos- 
sible to  say  which  of  the  other  elements  may  not  be  similarly 
capable  of  becoming  more  remote  constituents  of  organic  com- 
pounds (constituents  of  organic  radicals). 

With  these  compounds  we  must  not  confound  those  in  which 
organic  acids  are  combined  with  inorganic  bases,  or  organic  bases 
with  inorganic  acids,  such  as  tartrate  of  lead,  for  instance,  silicic 
ether,  borate  of  morphia,  etc. ;  'since  in  such  bodies  any  of  the  ele- 
ments may  of  course  occur. 

Organic  compounds  may  be  analyzed  either  with  a  view  simply 
to  resolve  them  into  their  proximate  constituents ;  thus,  for 
instance,  a  gum-resin  into  resin,  gum,  and  ethereal  oil ;  or  the 
analysis  may  have  for  its  object  the  determination  of  the  ultimate 
constituents  (the  elements)  of  the  substance.  The  simple  resolu- 


§  171.]  ORGANIC   ANALYSIS.  605 

tion  of  organic  compounds  into  their  proximate  constituents  is 
effected  by  methods  perfectly  similar  to  those  used  in  the  analysis 
of  inorganic  compounds ;  that  is,  the  operator  endeavors  to  sepa- 
rate (by  solvents,  application  of  heat,  etc.)  the  individual  constitu- 
ents from  one  another,  either  directly,  or  after  having  converted 
them  into  appropriate  forms.  We  disregard  here  altogether  this 
kind  of  organic  analysis — of  which  the  methods  must  be  nearly  as 
numerous  and  varied  as  the  cases  to  which  they  are  applied — and 
proceed  at  once  to  treat  of  the  second  kind,  which  may  be  called 
the  ultimate  analysis  of  organic  bodies. 

The  ultimate  analysis  of  organic  bodies  (here  termed  simply, 
organic  analysis)  has  for  its  object,  as  stated  above,  the  determi- 
nation of  the  elements  contained  in  organic  substances.  It  teaches 
us  how  to  isolate  these  elements  or  to  convert  them  into  com- 
pounds of  known  composition,  to  separate  the  new  compounds 
formed  from  one  another,  and  to  calculate  from  their  several 
weights,  or  volumes,  the  quantities  of  the  elements.  Organic 
analysis,  therefore,  is  based  upon  the  same  principle  upon  which 
rest  most  of  the  methods  of  separating  and  determining  inorganic 
compounds. 

The  conversion  of  most  organic  substances  into  distinctly 
characterized  and  readily  separable  products,  the  weights  of  which 
can  be  accurately  determined,  oilers  no  great  difficulties,  and 
organic  analysis  is  therefore  usually  one  of  the  more  easy  tasks  of 
analytical  chemistry ;  and  as,  from  the  limited  number  of  the  ele- 
ments which  constitute  organic  bodies,  there  is  necessarily  a  great 
sameness  in  the  products  of  their  decomposition,  the  analytical 
process  is  always  very  similar,  and  a  few  methods  suffice  for  all 
cases.  It  is  principally  ascribable  to  this  latter  circumstance  that 
organic  analysis  has  so  speedily  attained  its  present  high  degree  of 
perfection :  the  constant  examination  and  improvement  of  a  few 
methods  by  a  great  number  of  chemists  could  not  fail  to  produce 
this  result. 

An  organic  analysis  may  have  for  its  object  either  simply  to 
ascertain  the  relative  quantities  of  the  constituent  elements  of  a 
substance — thus,  for  instance,  woods  may  be  analyzed  to  ascertain 
their  heating  power,  fats  to  ascertain  their  illuminating  power — or 
to  determine  not  only  the  relative  quantities  of  the  constituent 
elementary  atoms,  but  also  the  number  of  atoms  of  carbon,  hydro- 
gen, oxygen,  &c.,  which  constitute  1  molecule  of  the  analyzed 


606  ORGANIC    ANALYSIS.  [§  172. 

compound.  In  scientific  investigations  we  have  invariably  the 
latter  object  in  view,  although  we  are  not  yet  able  to  achieve  it  in 
all  cases.  These  two  objects  cannot  well  be  attained  by  one  opera- 
tion ;  each  requires  a  distinct  process. 

The  methods  by  which  we  ascertain  the  proportions  of  the  con- 
stituent elements  of  organic  compounds  may  be  called  collectively 
the  ultimate  analysis  of  organic  bodies,  in  a  more  restricted 
sense  ;  whilst  the  methods  which  reveal  to  us  the  absolute  number 
of  elementary  atoms  constituting  the  molecule  of  the  analyzed 
compound  may  be  styled  the  determination  of  the  molecular 
weight  of  organic  bodies. 

The  success  of  an  organic  analysis  depends  both  upon  the 
method  and  its  execution.  The  latter  requires  patience,  circum- 
spection, and  skill;  whoever  is  moderately  endowed  with  these 
gifts  will  soon  become  a  proficient  in  this  branch.  The  selection 
of  the  method  depends  upon  the  knowledge  of  the  constituents  of 
the  substance,  and  the  method  selected  may  require  certain  modifi- 
cations, according  to  the  properties  and  state  of  aggregation  of  the 
same.  Before  we  can  proceed,  therefore,  to  describe  the  various 
methods  applicable  in  the  different  cases  that  may  occur,  we  have 
first  to  occupy  ourselves  here  with  the  means  of  testing  organic 
bodies  qualitatively. 

I.  QUALITATIVE  EXAMINATION  OF  ORGANIC  BODIES. 


It  is  not  necessary,  for  the  correct  selection  of  the  proper 
method,  to  know  all  the  elements  of  an  organic  compound,  since, 
for  instance,  the  presence  or  absence  of  oxygen  makes  not  the 
slighest  difference  to  the  method.  But  with  regard  to  other  ele- 
ments, such  as  nitrogen,  sulphur,  phosphorus,  chlorine,  iodine, 
bromine,  <fec.,  and  also  the  various  metals,  it  is  absolutely  indis- 
pensable that  the  operator  should  know  positively  whether  either 
of  them  is  present.  This  may  be  ascertained  in  the  following 
manner  : 

1.  Testing  for  Nitrogen. 

Substances  containing  a  tolerably  large  amount  of  nitrogen 
exhale  upon  combustion,  or  when  intensely  heated,  the  well-known 
smell  of  singed  hair  or  feathers.  No  further  test  is  required  if 


§172.]  ORGANIC    ANALYSIS.  607 

this  smell  is  distinctly  perceptible ;  otherwise  one  of  the  following 
experiments  is  resorted  to : 

a.  The  substance  is  mixed  with  hydrate  of  potassa  in  powder 
or  with  soda-lime  (§  66,  4  or  5),  and  the  mixture  heated  in  a  test- 
tube.    If  the  substance  contains  nitrogen,  ammonia  will  be  evolved, 
which  may  be  readily  detected  by  its  odor  and  reaction,  and  by 
the  formation  of  white  fumes  with  volatile  acids.     Should  these 
reactions  fail  to  afford   positive  certainty,  every  doubt   may  be 
removed  by  the  following  experiment :  Heat  a  somewhat  larger 
portion  of  the  substance  in  a  short  tube,  with  an  excess  of  soda- 
lime,  and  conduct  the  products   of   the   combustion  into  dilute 
hydrochloric  acid ;  evaporate  the  acid  on  the  water-bath,  dissolve 
die  residue  in  a  little  water,  and  mix  the  solution  with  platinic 
chloride  and  alcohol.     Should  no  precipitate  form,  even  after  the 
lapse  of  some  time,  the  substance  may  be  considered  free  from 
nitrogen. 

b.  LASSAIGXE  has  proposed  another   method,  which  is  based 
upon  the  property  of  potassium  to  form  potassium  cyanide  when 
ignited  with  a  nitrogenous  organic  substance.     The  following  is 
the  best  mode  of  performing  the  experiment : 

Heat  the  substance  under  examination,  in  a  test-tube,  with  a 
small  lump  of  potassium,  and  after  the  complete  combustion  of 
the  potassium,  treat  the  residue  with  a  little  water  (cautiously); 
filter  the  solution,  add  2  drops  of  solution  of  ferrous  sulphate  con- 
taining some  ferric  sulphate,  digest  the  mixture  a  short  time,  and 
add  hydrochloric  acid  in  excess.  The  formation  of  a  blue  or 
bluish-green  precipitate  or  coloration  proves  the  presence  of 
nitrogen. 

Both  methods  are  delicate  :  a  is  the  more  commonly  employed, 
and  suffices  in  almost  all  cases ;  b  does  not  answer  so  well  in  the 
case  of  alkaloids  containing  oxygen  (e.g.  morphia,  brucia). 

c.  In  organic  substances   containing   oxides  of   nitrogen,  the 
presence  of  nitrogen  cannot  be  detected  with  certainty  by  either  a 
or  &,  but  it  may  be  readily  discovered  by  heating  the  substance  in 
a  tube,  when  red  acid  fumes,  imparting  a  blue  tint  to  iodide  of 
starch  paper,  will  be  evolved,  accompanied  often  by  deflagration. 

2.  Testing  for  Sulphur. 

a-.  Solid  substances  are  fused  with  about  12  parts  of  pure 
hydrate  of  potassa  and  6  parts  of  potassium  nitrate.  Or  they  are 


608  ORGANIC    ANALYSIS.  [§  172. 

intimately  mixed  with  some  pure  potassium  nitrate  and  sodium 
carbonate ;  potassium  nitrate  is  then  heated  to  fusion  in  a  porcelain 
crucible,  and  the  mixture  gradually  added  to  the  fusing  mass. 
The  mass  is  allowed  to  cool,  then  dissolved  in  water,  and  the  solu- 
tion tested  with  barium  chloride,  after  acidifying  with  hydro- 
chloric acid. 

l>.  Fluids  are  treated  with  fuming  nitric  acid,  or  with  a  mixture 
of  nitric  acid  and  potassium  chlorate,  at  first  in  the  cold,  finally 
with  application  of  heat ;  the  solution  is  tested  as  in  a. 

c.  As  the  methods  a  and  b  serve  simply  to  indicate  the  presence 
of  sulphur  in  a  general  way,  but  afford  no  information  regarding 
the  state  or  form  in  which  that  element  may  be  present,  I  add 
here  another  method,  which  serves  to  detect  only  -the  sulphur  in 
the  non-oxidized  state  in  organic  compounds. 

Boil  the  substance  with  strong  solution  of  potassa  and  evap- 
orate nearly  to  dryness.  Dissolve  the  residue  in  a  little  water,  and 
bring  the  solution  into  a  small  flask  provided  with  a  loosely-fitting 
stopper,  through  which  passes  a  funnel  tube  reaching  nearly  to  the 
bottom  of  the  flask.  Suspend  from  the  lower  surface  of  the 
stopper  within  the  flask  a  strip  of  paper  dipped  first  in  lead 
acetate,  then  in  ammonium  carbonate  solution.  Add  slowly  dilute 
sulphuric  acid,  and  observe  whether  the  lead  paper  becomes  brown  ; 
or  test  the  first  alkaline  solution  by  means  of  a  polished  surface  of 
silver,  or  by  nitroprusside  of  sodium,  or  by  just  acidifying  the 
dilute  solution  with  hydrochloric  acid,  and  adding  a  few  drops  of 
a  mixture  of  ferric  chloride  and  potassium  ferricyanide  (see  "  Qual. 
Anal."  §  159). 

3.  Testing  for  Phosphorus. 

The  methods  described  in  2,  a  and  J,  may  likewise  serve  for 
phosphorus.  The  solutions  obtained  are  tested  for  phosphoric  acid 
with  magnesium  sulphate  or  chloride  ;  or  with  ferric  chloride,  with 
addition  of  sodium  acetate ;  or  with  solution  of  molybdie  acid 
(comp.  "  Qual.  Anal.").  In  method  b,  the  greater  part  of  the 
excess  of  nitric  acid  must  first  be  removed  by  evaporation. 

4.  Testing  for  Inorganic  Substances. 

A  portion  of  the  substance  is  heated  on  platinum  foil,  to  see 
whether  or  not  a  residue  remains.  When  acting  upon  difficultly 
combustible  substances,  the  process  may  be  accelerated  by  heating 
the  spot  which  the  substance  occupies  on  the  platinum  foil  to  the 


§  173.]  .  ORGANIC    ANALYSIS.  609 

most  intense  redness,  by  directing  the  flame  of  the  blow-pipe  upon 
it  from  below.  The  residue  is  then  examined  by  the  usual 
methods.  That  volatile  metals  in  volatile  organic  compounds 
— e.g.,  arsenic  in  kakodyl — cannot  be  detected  by  this  method 
need  hardly  be  mentioned. 

These  preliminary  experiments  should  never  be  omitted,  since 
neglect  in  this  respect  may  give  rise  to  very  great  errors.  Thus, 
for  instance,  taurin,  a  substance  in  which  a  large  proportion  of 
sulphur  was  afterwards  found  to  exist,  had  originally  the  formula 
C4JST2H14OIO  assigned  to  it.  The  preliminary  examination  of  organic 
substances  for  chlorine,  bromine,  and  iodine  is  generally  unneces- 
sary, as  these  elements  do  not  occur  in  native  organic  compounds, 
and  as  their  presence  in  compounds  artificially  produced  by  the 
action  of  the  halogens  requires  generally  no  further  proof.  Should 
it,  however,  be  desirable  to  ascertain  positively  whether  a  substance 
does  or  does  not  contain  chlorine,  iodine,  or  bromine,  this  may  be 
done  by  the  methods  given  §  188. 

II.  DETERMINATION  OF  THE  ELEMENTS  IN  ORGANIC  BODIES.* 

§  178. 

A.  ANALYSIS  OF  COMPOUNDS   WHICH   CONSIST   SIMPLY  OF   CARBON 
AND  HYDROGEN,  OR  OF  CARBON,  HYDROGEN,  AND  OXYGEN. 

The  principle  of  the  method  which  serves  to  effect  the  quanti- 
tative analysis  of  such  compounds  is  exceedingly  simple.  The 
substance  is  burned  to  carbonic  acid  and  water ;  these  products  are 
separated  from  each  other  and  weighed,  and  the  carbon  of  the 
substance  is  calculated  from  the  weight  of  the  carbonic  acid,  the 
hydrogen  from  that  of  the  water.  If  the  sum  -of  the  carbon  and 
hydrogen  is  equal  to  the  original  weight  of  the  substance,  the 
substance  contains  no  oxygen  ;  if  it  is  less  than  the  weight  of  the 
substance,  the  difference  expresses  the  amount  of  oxygen  present. 

The  combustion  is  effected  either  by  igniting  the  organic  sub- 
stance with  oxygenized  bodies  which  readily  part  with  their 
oxygen  (cupric  oxide,  lead  chromate,  &c.) ;  or  at  the  expense 
both  of  free  and  combined  oxygen. 

a.  SOLID  BODIES. 

*  [For  Prof.  Warren's  admirable  methods  we  must  refer  to  his  original  papers 
in  Am.  Journ.  Sci.,  3d  ser.,  vol.  38,  p.  387,  vol.  41,  p.  40,  and  vol.  42,  p.  156.] 


610 


ORGANIC   ANALYSIS.. 


[ 


COMBUSTION  WITH  CUPRIC  OXIDE. 

Applicable  (with  modification  described  in  §  176)  to  non-volatile 
organic  compounds  not  containing  chlorine,  bromine,  iodine, 
alkali  metals,  alkali-earth  metals,  nitrogen,  or  sulphur. 

§174. 
I.  APPARATUS  AND  PREPARATIONS  REQUIRED  FOR  THE  ANALYSIS. 

1.  THE  SUBSTANCE. — This  must  be  most  finely  pulverized  and 
perfectly  pure  and  dry ; — for  the  method  of  drying,  I  refer  to  §  26. 

2.  A  TUBE  IN  WHICH  TO  WEIGH  THE  SUBSTANCE,  made  of  thin 
glass  about  20  cm.  long,  and  of  7  mm.  internal  diameter ;  one  end 
of  the  tube  is  closed  by  fusion ;  the  other,  during  the  operation  of 
weighing,  is  stopped  with  a  smooth  cork. 

3.  THE  COMBUSTION  TUBE. — A  tube  of  difficultly  fusible  glass 
(potassa  glass),  about  2  mm.  thick  in  the  glass,  80  to  90  cm.  in 
length,  and  from  12  to  14  mm.  inner  diameter,  is  softened  in  the 
middle  before  a  glass-blower's  lamp,  drawn  out  as  represented  in 
fig.  71,  and  finally  apart  at  b.     The  fine  points  of  the  two  pieces. 


FIG.  71. 


are  then  sealed  and  thickened  a  little  in  the  flame,  and  the  sharp 
edges  of  the  open  ends,  a  and  c,  are  slightly  rounded  by  fusion, 
care  being  taken  to  leave  the  aperture  perfectly  round.  The 
posterior  part  of  .the  tube  should  be  shaped  as  shown  in  fig.  72, 
and  not  as  in  fig.  73. 


FIG.  72. 


FIG.  73. 


Two  perfect  combustion  tubes  are  thus  produced.  The  one 
intended  for  immediate  use  is  cleaned  with  linen  or  paper  attached 
to  a  piece  of  wire,  and  then  thoroughly  dried.  This  is  effected 
either  by  laying  the  tube,  with  a  piece  of  paper  twisted  over  its 


174. 


ORGANIC   ANALYSIS. 


611 


mouth,  for  some  time  on  a  sand-bath,  with  occasional  removal  of 
the  air  from  it  by  suction,  with  the  aid  of  a  glass  tube,  or  (rapidly) 
by  moving  the  tube  to  and  fro  over  the  flame  of  a  gas  or  spirit 
lamp,  heating  its  entire  length,  and  continually  removing  the  hot 
air  by  suction  through  the  small  glass  tube  (Fig.  74). 


FIG.  74. 

The  combustion  tube,  when  quite  dry,  is  closed  air-tight  with 
a  cork,  and  kept  in  a  warm  place  until  required  for  use. 

In  default  of  glass  tubes  possessed  of  the  proper  degree  of 
infusibility,  thin  brass  or  copper  foil,  or  brass  gauze,  is  rolled 
round  the  tube,  and  iron  wire  coiled  round  it. 

4.  THE  POTASH  BULBS  (fig.  75). — This  apparatus,  devised  by 
LIEBIG,  is  filled  to  the  extent  indicated  in  the  engraving,  with  a 
clear  solution  of  caustic  potassa  of  1*27 

SP-  gr-  (§  6$,  '0-  The  introduction  of 
the  solution  of  potassa  into  the  apparatus 
is  effected  by  plunging  the  end  a  into  a 
beaker  or  dish  into  which  a  little  of  the 
solution  has  been  poured  out,  and  apply- 
ing suction  to  b,  by  means  of  a  caoutchouc 
tube.  The  two  ends  are  then  wiped  per- 
fectly dry  with  twisted  slips  of  paper, 
and  the  outside  of  the  apparatus  with  a 
clean  cloth.  FlG-75- 

5.  THE  CALCIUM  CHLORIDE  TUBE   (fig.   76)   is  filled   in    the 
following  manner : — In  the  first  place,  the  neck  between  the  two 
bulbs  of  the  tube  is  loosely  stopped  with  a  small  cotton  plug ;  this 
is  effected  by  introducing  a  loose  cotton  plug  into  the  wide  tube, 
and  applying  a  sudden  and  energetic  suction  at  the  other  end. 
The  large  bulb  is  then  filled  with   lumps   of   calcium   chloride 
(§  66,  8,  #),  and  the  tube  with  smaller  fragments,  intermixed  with 
coarse  powder  of  the  same  substance .;  a  loose  cotton  plug  is  then 
inserted,  and  the  tube  finally  closed  with  a  perforated  cork,  into 
which  a  small  glass  tube  is  fitted  ;  the  protruding  part  of  the  cork 


612  ORGANIC    ANALYSIS.  [§  174. 

is  cut  off,  and  the  cut  surface  covered  over  with  sealing-wax ;  the 
edge  of  the  little  tube  is  slightly  rounded  by  fusion. 

In  using  this  tube  a  considerable  quantity  of  the  water  con- 
denses in  the  empty  bulb  a,  and  at  the  close  of  the  experiment 


FIG.  76. 

may  be  poured  out.  The  operator  is  thus  enabled  to  test  it  as  to 
reaction,  &c.,  and  also  to  use  the  same  tube  far  oftener  without 
fresh  filling  than  he  could  otherwise. 

6.  A  SMALL  TUBE  OF  VULCANIZED  INDIA-RUBBER. — This  must 
be  so  narrow  that  it  can  only  be  pushed  with  difficulty  over  the 
tube  of  the  calcium  chloride  tube  on  the  one  hand,  and  over  the 
end  of  the  potash  bulbs  on  the  other  hand ;  in  which  case  there  is 
no  need  of  binding  with  silk  cord.     If  the  rubber  tube  should  be 
a  little  too  wide,  it  must  be  tied  round  with  silk  cord,  or  with 
ignited  piano  wire.      It  is  self-evident  that  the  narrow  end  of  the 
calcium  chloride  tube  should  be  of  the  same  width  as  the  tube  a  of 
the  potash  bulbs.     The  india-rubber  tube  is  purified  from  any 
adherent  sulphur,  and  dried  in  the  water-bath  previous  to  use. 

7.  CORKS. — These  should   be   soft   and   smooth,  and   as   free 
as  possible  from  visible  pores.     A  cork  should  be  selected  which, 
.after  careful  squeezing,  fits  perfectly  tight,  and  screws  with  some 
difficulty  to  one-third  of  its  length,  at  the  most,  into  the  mouth  of 
the  combustion  tube;   a  perfectly  smooth  and  round   hole,  into 
which  the  end  b  of  the  chloride  of  calcium  tube  must  fit  perfectly 
air-tight,  is  then  carefully  bored  through  the  axis  of  the  cork. 
The  cork  is  then  kept  for  an  hour  of  two  in  the  water-bath.     It  is 
advisable  always   to  have   two   corks  of  this  description  ready. 
Instead  of  ordinary  corks,  caoutchouc  stoppers  may  be  used  with 
great  advantage. 

8.  OXIDE  OF  COPPER. — A  Hessian  crucible,  of  about  100  c.c. 
capacity,  is  nearly  filled  with  oxide  of  copper  prepared  as  directed 
in  §  66,  1 ;  the  crucible   is   covered  with   a  well-fitting  overlap- 
ping lid,  and  heated  to  dull  redness  with  charcoal,  or  in  a  suitable 
gas-furnace ;  it  is  then  allowed  to  cool,  so  that  by  the  time  the 
oxide  of  copper  is  required  for  use,  the  hand  can  only  just  bear 
contact  with  it. 


§  174.] 


OKGANIC   ANALYSIS. 


613 


9.  A  WIDE  GLASS  TUBE  sealed  at  one  end,  or  a  FLASK  (fig.  77), 
in  which  the  freshly  ignited  oxide  of  copper  is  allowed  to  cool, 
and  from  which  it  is  transferred  to  the  combustion  tube, 
secure  from  the  possible  absorption  of  moisture  from  the  air. 

The  freshly  ignited  and  still  quite  hot  oxide  of  copper 
is  transferred  direct  from  the  crucible  to  this  filling  tube, 
or  flask,  which  is  then  closed  air-tight  with  a  cork.  It 
saves  time  to  fill  in  at  once  a  sufficient  quantity  of  oxide  to 
last  for  several  analyses.  If  the  cork  fits  tight,  the  con- 
tents will  remain  several  days  fit  for  use,  even  though  a 
portion  has  been  taken  out,  and  the  tube  repeatedly  opened.  Fig-  77. 

10.  A  MIXING  WERE  of  copper  (fig.  78)  with  ring  at  one  end 


Fig.  78. 

for   a  handle  and  a  single   corkscrew  turn   at  the  other,  which 
should  taper  smoothly  to  a  point. 

D  ^  11.    A     COMBUSTION-FURNACE. — 

Some  time  ago  the  only  one  used 
was  LIEBIG'S,  in  which  charcoal  is 
the  fuel.'  Eecently  gas  combustion 
furnaces  have  been  introduced  into 
most  laboratories,  because  they  are 


Fig.  79. 


more  cleanly  and  convenient. 

a.  LIEBIG'S  combustion-furnace  is  of  sheet-iron.  It  has  the 
form  of  a  long  box,  open  at  the  top  and  behind.  It  serves  to  heat 
the  combustion  tube  with  red-hot  charcoal.  Fig.  79  represents  the 
furnace  as  seen  from  the  top. 

It  is  from  50  to  60  cm.  long,  and  from  7  to  8  deep ;  the  bot- 
tom, which,  by  cutting  small  slits  in  the  sheet-iron,  is  converted 
into  a  grating,  has  a  width  of  about  7  cm.  The  side  walls  are 
inclined  slightly  outward,  so  that  at  the  top  they  stand  about  12 


Fig.  80. 


Fig.  81. 


cm.  apart.     A  series  of  upright  pieces  of  strong  sheet-iron,  having 
the  form  shown  in  Z>,  fig.  80,  and  riveted  on  the  bottom  of  the 


614  ORGANIC  ANALYSIS.  [§  175. 

furnace  at  intervals  of  about  5  cm.,  serves  to  support  the  com- 
bustion tube.  They  must  be  of  exactly  corresponding  height  with 
the  round  aperture  in  the  front  piece  of  the  furnace  (fig.  80,  A). 

This  aperture  must  be  sufficiently  large  to  admit  the  com- 
bustion tube  easily.  Of  the  two  screens  used,  one  has  the  form 
shown  in  fig.  81,  the  other  is  a  single  plate  precisely  like 
the  end  piece  of  the  furnace  (fig.  79).  The  openings  cut  into  the 
screens  must  be  sufficiently  large  to  receive  the  combustion  tube 
without  difficulty.  The  furnace  is  placed  upon  two  bricks  resting 
upon  a  flat  surface,  and  is  slightly  raised  at  the  farther  end,  by 
inserting  a  piece  of  wood  between  the  supports  (see  fig.  84).  The 
apertures  of  the  grating  at  the  anterior  end  of  the  furnace  must 
not  be  blocked  up  by  the  supporting  bricks.  In  cases  where  the 
combustion  tubes  are  of  good  quality,  the  furnace  may  be  raised 
by  introducing  a  little  iron  rod  between  the  furnace  and  the 
supporting  brick.  Placing  the  tube  in  a  gutter  of  Kussia  sheet- 
iron  tends  greatly  to  preserve  it,  but  contact  of  the  glass  and  iron 
must  be  prevented  by  an  intervening  layer  of  asbestos. 

I.  Gas  combustion  furnaces  of  the  most  various  descriptions 
have  been  proposed. 

§175. 
II.  PERFORMANCE  OF  THE  ANALYTICAL  PROCESS. 

a.  Weigh  first  the  potash  apparatus,  then  the  calcium  chloride 
tube.  Introduce  about  0'35 — 0'6  grin,  of  the  substance  under 
examination  (more  or  less,  according  as  it  is  rich  or  poor  in 
oxygen)  into  the  weighing  tube,*  which  must  be  no  longer  warm, 
and  weigh  the  latter  accurately  with  its  contents.  The  weight  of 
the  empty  tube  being  approximately  known,  it  is  easy  to  take  the 
right  quantity  of  substance  required  for  the  analysis.  Close  the 
tube  then  with  a  smooth  cork. 

~b.  The  filling  of  the  combustion  tube  is  effected  as  follows : 
The  perfectly  dry  tube  is  rinsed  with  some  oxide  of  copper; 
a  layer  of  oxide  of  copper,  about  13  cm.  long,  is  introduced  into 
the  posterior  end  of  the  combustion  tube,  by  inserting  the  latter 
into  the  filling  tube  or  flask  containing  the  oxide  of  copper 

*  Care  must  be  taken  that  no  particles  of  the  substance  adhere  to  the  sides  of 
the  tube,  at  least  not  at  the  top. 


175.] 


ORGANIC   ANALYSIS. 


615 


(fig.  82),  holding  both  tubes  in  an  oblique  direction,  and  giving  a 
few  gentle  taps. 


Fig.  82. 

From  the  tube  containing  the  substance  remove  the  cork 
cautiously,  to  prevent  the  slightest  loss  of  substance ;  insert  the 
open  end  of  the  tube  as  deep  as  possible  into  the  combustion  tube, 
and  pour  from  it  the  requisite  quantity  of  substance  by  giving  it 
a  few  turns,  pressing  the  rim  all  the  while  gently  against  the 
upper  side  of  the  combustion  tube,  to  prevent  its  coming  into 
contact  with  the  powder  already  poured  out ;  the  two  tubes  are,  in 
this  manipulation,  held  slightly  inclined  (see  fig.  83). 


Fig.  83. 

When  a  sufficient  quantity  of  the  substance  has  been  thus 
transferred  from  the  weighing  to  the  combustion  tube,  the  latter 
is  restored  to  the  horizontal  position,  which  gives  to  the  former  a 
gentle  inclination  with  the  closed  end  downwards.  If  the  little 
tube  is  now  slowly  withdrawn,  with  a  few  turns,  the  powder  near 
the  border  of  the  opening  falls  back  into  it,  leaving  the  opening 
free  for  the  cork.  The  tube  is  then  immediately  corked  and 
weighed,  the  combustion  tube  also  being  meanwhile  kept  closed 
with  a  cork.  The  difference  between  the  two  weighings  shows 
the  quantity  of  substance  transferred  from  the  weighing  to  the 
combustion  tube.  The  latter  is  then  again  opened,  and  a  quantity 
of  oxide  of  copper,  equal  to  the  first,  transferred  to  it  from  the 
filling  tube,  or  flask,  taking  care  to  rinse  down  with  this  the 
particles  of  the  substance  still  adhering  to  the  sides  of  the  tube. 


616  ORGANIC   ANALYSIS.  [§  175. 

There  is  now  in  the  hind  part  of  the  tube  a  layer  of  oxide  of 
copper,  about  25  cm.  long,  with  the  substance  in  the  middle. 

The  next  operation  is  the  mixing  :  this  is  performed  with  the 
aid  of  the  wire  (fig.  78),  which  is  pushed  down  to  within  3  to  4 
cm.  of  the  end,  and  rapidly  moved  about  in  all  directions  until 
the  mixture  is  complete  and  uniform,  the  tube  being  held  nearly 
horizontal. 

Oxide  of  copper  is  then  poured  in  to  within  5  to  6  cm.  of  the 
open  end,,  and  the  tube  is  corked. 

c.  A  few  gentle  taps  on  the  table  will  generally  suffice  to  shake 
together  the  contents  of  the  tube,  so  as  to  completely  clear  the 
tail  from  oxide  of  copper,  and  leave  a  free  passage  for  the  evolved 
gas   from   end   to   end.     Should    this    fail,    as   will    occasionally 
happen,  owing  to  malformation  of  the  tail,  the  object  in  view  may 
be  attained  by  striking  the  mouth  of  the  tube  several  times  against 
the  side  of  a  table. 

d.  Connect  the  end  b  (fig.  84)  of  the  weighed  calcium  chloride 
tube  with  the  combustion  tube  by  means  of  a  dried  perforated 
cork,  lay  the  furnace  upon  its  supports,  with  a  slight  inclination 
forward,  and  place  the  combustion  tube  in  it ;    connect  the  end 


Fig.  84. 

of  the  calcium  chloride  tube,  by  means  of  a  vulcanized  india- 
rubber  tube,  with  the  end  m  of  the  potash  apparatus,  and,  if 
necessary,  secure  the  connection  with  silk  cord,  taking  care  to 
press  the  joint  of  the  two  thumbs  close  together  whilst  tightening 
the  cords,  since  otherwise,  should  one  of  the  cords  happen  to  give 
way,  the  whole  apparatus  might  be  broken.  Rest  the  potash 
apparatus  upon  a  folded  piece  of  cloth.  Fig.  84  shows  the  whole 
arrangement. 

e.  To  ascertain  whether  the  joinings  of  the  apparatus  fit  air- 
tight,  put  a  piece  of  wood  about  the  thickness  of  a  finger  (*),  or  a 


§  175.]  ORGANIC   ANALYSIS.  617 

cork  or  other  body  of  the  kind,  undeT  the  bulb  r  of  the  potash 
apparatus,  so  as  to  raise  that  bulb  slightly  (see  fig.  84).  Heat  the 
bulb  m,  by  holding  a  piece  of  red-hot  charcoal  near  it,  until  a 
certain  amount  of  air  is  driven  out  of  the  apparatus ;  then  remove 
the  piece  of  wood  («),  and  allow  the  bulb  m  to  cool.  The  solution 
of  potassa  will  now  rise  into  the  bulb  m,  filling  it  more  or  less ;  if 
the  liquid  in  m  preserves,  for  the  space  of  a  few  minutes,  the. 
same  level  which  it  has  assumed  after  the  perfect  cooling  of  the 
bulb,  the  joinings  may  be  considered  perfect ;  should  the  fluid,  on 
the  other  hand,  gradually  regain  its  original  level  in  both  limbs  of 
the  apparatus,  this  is  a  positive  proof  that  the  joinings  are  not  air- 
tight. (The  few  minutes  which  elapse  between  the  two  observa- 
tions may  be  advantageously  employed  in  reweighing  the  little 
tube  in  which  the  substance  intended  for  analysis  was  originally 
weighed.) 

f.  Let  the  mouth  of  the  combustion  tube  project  a  full  inch 
beyond  the  furnace ;  suspend  the  single  screen  over  the  anterior 
end  of  the  furnace,  as  a  protection  to  the  cork ;  put  the  double 
screen  over  the  combustion  tube  about  two  inches  farther  on  (see 
fig.  84),  replace  the  little  piece  of  wood  (s)  under  r,  and  put  small 
pieces  of  red-hot  charcoal  first  under  that  portion  of  the  tube 
which  is  separated  by  the  screen ;  surround  this  portion  gradually 
altogether  with  ignited  charcoal,  and  let  it  get  red-hot ;  then  shift 
the  screen  an  inch  farther  back,  surround  the  newly  exposed 
portion  of  the  tube  also  with  ignited  charcoal,  and  let  it  get  red- 
hot  ;  and  proceed  in  this  manner  slowly  and  gradually  extending 
the  application  of  heat  to  the  tail  of  the  tube,  taking  care  to  wait 
always  until  the  last  exposed  portion  is  red-hot  before  shifting  the 
screen,  and  also  to  maintain  the  whole  of  the  exposed  portion  of 
the  tube  before  the  screen  in  a  state  of  ignition,  and  the  projecting 
part  of  it  so  hot  that  the  fingers  can  hardly  bear  the  shortest  con- 
tact with  it.  The  whole  process  requires  generally  from  f  to  1  hour. 
It  is  quite  superfluous,  and  even  injudicious,  to  fan  the  charcoal 
constantly ;  this  should  be  done  however  when  the  process  is  draw- 
ing to  an  end,  as  we  shall  immediately  have  occasion  to  notice. 

The  liquid  in  the  potash  bulbs  is  gradually  displaced  from  the 
bulb  in  upon  the  application  of  heat  to  the  anterior  portion  of  the 
combustion  tube,  owing  simply  to  the  expansion  of  the  heated  air. 
The  evolution  of  gas  proceeds  with  greater  briskness  when  the 
heat  begins  to  reach  the  actual  mixture ;  the  first  bubbles  are  only 


618  ORGANIC    ANALYSIS.  [§  175. 

partly  absorbed,  as  the  carbonic  acid  contains  still  an  admixture  of 
air ;  but  those  which  follow  are  so  completely  absorbed  by  the 
potassa,  that  a  solitary  air-bubble  only  escapes  from  time  to  time 
through  the  liquid.  The  process  should  be 
conducted  in  a  manner  to  make  the  gas- 
bubbles  follow  each  other  at  intervals  of 
from  £  to  1  second.  Fig.  85  shows  the 
oper  position  of  the  potash  bulbs  during 
the  operation. 

It  will  be  seen  from  this  that  an  air- 
bubble  entering  through  m  passes  first  into 
the  bulb  &,  thence  to  <?,  from  c  to  d,  and 
passing  over  the  solution  in  the  latter, 
escapes  finally  into  the  bulb  /*,  through  the 
fluid  which  just  covers  the  mouth  of  the  tube  e. 

g.  "When  the  tube  is  in  its  whole  length  surrounded  with  red- 
hot  charcoal,  and  the  evolution  of  gas  "has  relaxed,  fan  the  burning 
charcoal  gently  with  a  piece  of  pasteboard.  When  the  evolution  of 
gas  has  entirely  ceased,  adjust  the  position  of  the  potash  bulbs  to  a 
level,  remove  the  charcoal  from  the  farther  end  of  the  tube,  and 
place  the  screen  before  the  tail.  The  ensuing  cooling  of  the  tube 
on  the  one  hand,  and  the  absorption  of  the  carbonic  acid  in  the 
potash  bulbs  on  the  other,  cause  the  solution  of  potassa  in  the 
latter  to  recede,  slowly  at  first,  but  with  increased  rapidity  from 
the  moment  the  liquid  reaches  the  bulb  m.  (If  you  have  taken 
care  to  adjust  the  position  of  the  potash  bulbs  correctly,  you  need 
not  fear  that  the  contents  of  the  latter  will  recede  to  the  calcium 
chloride  tube.)  When  the  bulb  m  is  about  half  filled  with  solution 
of  potassa,  break  off  the  point  of  the  combustion  tube  with  a  pair 
of  pliers  or  scissors,  whereupon  the  fluid  in  the  potash  bulbs  will 
immediately  resume  its  level.  Restore  the  potash  bulbs  now  again 
to  their  original  oblique  position,  join  a  caoutchouc  tube  to  the 
potash  bulbs,  and  slowly  apply  suction  until  the  last  bubbles  no 
longer  diminish  in  size  in  passing  through  the  latter.  It  is  better 
to  employ  a  small  aspirator  instead  of  sucking  with  the  mouth. 
You  then  know  the  volume  of  air  that  has  passed  through  the 
apparatus. 

This  terminates  the  analytical  process.  Disconnect  the  pot- 
ash bulbs  and  remove  the  calcium  chloride  tube,  together  with 
the  cork,  which  must  not  be  charred,  from  the  combustion  tube ; 


§  175.]  ORGANIC   ANALYSIS.  619 

remove  the  cork  also  from  the  calcium  chloride  tube,  and  place  the 
latter  upright,  with  the  bulb  upwards.  After  the  lapse  of  half  an 
hour,  weigh  the  potash  bulbs  and  the  calcium  chloride  tube,  and 
then  calculate  the  results  obtained.  They  are  generally  very  satis- 
factory. As  regards  the  carbon,  they  are  rather  somewhat  too  low 
(about  Ol  per  cent.)  than  too  high.  The  carbon  determination, 
indeed,  is  not  free  from  sources  of  error ;  but  none  of  these  inter- 
fere materially  with  the  accuracy  of  the  results,  and  the  deficiency 
arising  from  the  one  is  partially  balanced  by  the  excess  arising 
from  the  other.  In  the  first  place,  the  air  which  passes  through 
the  solution  of  potassa  during  the  combustion,  and  finally  during 
the  process  of  aspiration,  carries  away  with  it  a  minute  amount  of 
moisture.  The  loss  arising  from  this  cause  is  increased  if  the 
evolution  of  gas  proceeds  very  briskly,  since  this  tends  to  heat  the 
solution  of  potassa ;  and  also  if  nitrogen  or  oxygen  passes  through 
the  potash  bulbs  (compare  §  176  and  §  178).  This  may  be 
remedied,  however,  by  fixing  to  the  exit  end  of  the  latter  a  tube, 
either  straight  or  U-formed  (see  fig.  86  or  fig.  60);  the  tube 
may  be  filled  with  small  fragments  of  potassa,  or  one-half  may  be 
filled  with  soda  lime  (§66,  4)  and  the  other  half  with  calcium 
chloride,  the  end  containing  soda  lime  being  connected  to  the 
potash  apparatus,  which  is  always  weighed  along  with  the  appended 
tube.  In  the  second  place,  traces  of  carbonic  acid  from  the 
atmosphere  are  carried  into  the  potash  apparatus  during  the  final 
aspiration ;  this  may  be  avoided  by  connecting  the  tail  of  the  com- 
bustion tube  during  the  aspiration  with  a  tube  filled  with  potassa 
crushed  to  small  lumps,  by  means  of  a  flexible  tube.  In  the  third 
place,  it  may  happen  in  the  analysis  of  substances  containing  a 
considerable  proportion  of  water  or  hydrogen,  that  the  carbonic 
acid  is  not  completely  dried  in  passing  through  the  calcium 
chloride ;  this  may  be  avoided  by  using  instead  of  the  calcium 
chloride  tube,  or  in  conjunction  with  it,  a  U-tube  filled  with  frag- 
ments of  pumice  stone  and  H3SO4 ;  but  usually  a  calcium  chloride 
tube,  if  filled  for  about  12  c.c.  of  its  length  with  not  too  coarsely 
granulated  calcium  chloride,  will  suffice,  provided  the  combustion 
is  not  pushed  too  rapidly.  Finally,  if  the  mixture  was  not  suffi- 
ciently intimate,  traces  of  carbon  will  remain  unconsumed.  It  is 
therefore  better  to  complete  the  combustion  in  oxygen  gas.  See 
below. 


620  ORGANIC   ANALYSIS.  [§  177. 

§  176. 

[Completion  of  the  Combustion  by  Oxygen  Gas.  To  insure  the 
oxidation  of  the  last  traces  of  carbon  and  to  leave  the  oxide  of 
copper  ready  for  use  again,  it  is  advisable  to  finish  the  combustion 
in  a  stream  of  oxygen.  For  this  purpose  the  tail  of  the  combus- 
tion tube  must  be  made  rather  stout  and  long.  When  the  potash- 
lye  recedes,  slip  tightly  over  the  suitably  cooled  tail  a  caoutchouc 
tube  connected  with  a  source  of  pure  and  dry  oxygen  gas,  nip  off 
the  tip  within  this  tube  by  help  of  a  pliers,  and  cautiously  let  on 
the  oxygen  until  the  reduced  copper  is  oxidized  and  the  gas 
traverses  the  potash  bulbs.  Then  replace  the  stream  of  oxygen  by 
one  of  pure  and  dry  air,  to  remove  all  oxygen  from  the  bulbs. 
To  prevent  loss  by  evaporation  from  the  potash-lye,  append  to  the 
potash  bulb  the  additional  absorbing  apparatus  above  mentioned 
(in  §  ITS). 

The  oxygen  and  purified  air  are  supplied  as  in  the  process 
described  in  §  ITS.] 

COMBUSTION  WITH  LEAD  CHROMATE,  OR  WITH  LEAD  CHROMATE 
AND  POTASSIUM  DICHROMATE. 

§  177. 

This  is  not  only  a  good  method  for  the  analysis  of  compounds 
mentioned  in  §  1T4,  but  is  especially  resorted  to  in  the  analysis  of 
salts  of  organic  acids  with  alkalies  or  alkali-earth  metals  (as  the 
chromic  acid  completely  displaces  carbonic  acid  from  their  car- 
bonates), and  of  bodies  containing  sulphur,  chlorine,  bromine,  or 
iodine,  and  also  for  the  combustion  of  substances  containing  carbon 
in  a  difficultly  oxidizable  form — e.g.,  graphite. 

Of  the  apparatus,  &c.,  enumerated  in  §  1T4,  all  are  required 
except  oxide  of  copper,  which  is  here  replaced  by  lead  chromate 
(§  66,  2).  A  narrow  combustion  tube  may  be  selected,  as  lead 
chromate  contains  a  much  larger  amount  of  available  oxygen  in  an 
equal  volume  than  oxide  of  copper.  A  quantity  of  the  chromate, 
more  than  sufficient  to  fill  the  combustion  tube,  is  heated  in  a 
platinum  or  porcelain  dish  over  a  gas  or  BERZELIUS  lamp,  until  it 
begins  to  turn  brown ;  before  filling  it  into  the  tube,  it  is  allowed 
to  cool  down  to  100°  ;  and  even  below.  The  process  is  conducted 
as  the  one  described  in  §  174. 


§  178.]  OKGANIC   ANALYSIS.  621 

If  the  substance  analyzed  contains  a  large  proportion  of  sulphur, 
use  a  rather  long  combustion  tube  (60-70  cm.)  and  place  in  front 
of  the  mixture  10-20  cm.  pure  lead  chromate,  which  should  be 
kept  only  at  a  dull  red  heat  during  the  combustion  (CARIUS). 

One  of  the  principal  advantages  which  lead  chromate  has  over 
oxide  of  copper  as  an  oxidizing  agent  being  its  property  of  fusing 
at  a  high  heat,  the  temperature  must,  in  the  last  stage  of  the 
process  of  combustion,  be  raised  (by  fanning  the  charcoal,  &c.) 
sufficiently  high  to  fuse  the  contents  of  the  tube  completely,  as  far 
as  the  substance  extends.  To  heat  the  anterior  end  of  the  tube 
to  the  same  degree  of  intensity  would  be  injudicious,  since  the 
lead  chromate  in  that  part  would  thereby  lose  all  porosity,  and 
thus  also  the  power  of  effecting  the  combustion  of  the  products  of 
decomposition  which  may  have  escaped  oxidation  in  the  other 
parts  of  the  tube. 

As  the  lead  chromate,  even  in  powder,  is,  on  account  of  its 
density,  by  no  means  all  that  could  be  desired  in  this  latter  respect, 
it  is  preferable  to  fill  the  anterior  part  of  the  tube,  instead  of  with 
lead  chromate,  with  coarsely  pulverized  strongly  ignited  oxide  of 
copper,  or  with  copper  turnings  which  have  been  superficially  oxid- 
ized by  ignition  in  a  muffle  or  in  a  crucible  with  access  of  air. 

In  the  case  of  very  difficultly  combustible  substances — e.g., 
graphite — it  is  desirable  that  the  mass  should  not  only  readily 
cake,  but  also,  in  the  last  stage  of  the  process,  give  out  a  little 
more  oxygen  than  is  given*  out  by  lead  chromate.  It  is  therefore 
advisable  in  such  cases  to  add  to  the  latter  one-eighth  of  its  weight 
of  fused  and  powdered  potassium  dichromate.  With  the  aid  of 
this  addition,  complete  oxidation  of  even  very  difficultly  com- 
bustible bodies  may  be  effected  (LIEBIG). 


COMBUSTION  WITH  OXIDE  OF  COPPER  IN  A  STREAM  OF 
OXYGEN  GAS. 

§178. 

Many  chemists  effect  combustion  with  oxide  of  copper  in  a 
stream  of  oxygen  supplied  by  a  gasometer.  The  methods  based 
upon  this  principle  are  employed  not  only  for  the  analysis  of 
difficultly  combustible  bodies,  but  also  to  effect  the  determination 
of  the  carbon  and  hydrogen  in  organic  substances  in  general. 


622  ORGANIC   ANALYSIS.  [§  178. 

These  methods  require  a  gasometer  filled  with  oxygen,  and 
another  with  air,  together  with  certain  arrangements  to  dry  the 
oxygen  and  air  completely,  and  to  free  them  from  carbonic  acid. 
They  are  resorted  to  in  cases  where  a  number  of  ultimate  analyses 
have  to  be  made  in  succession ;  and  also  more  particularly  in  the 
analysis  of  substances  which  cannot  be  reduced  to  powder,  and  do 
not  admit  therefore  of  intimate  mixture  with  oxide  of  copper,  &c. 

The  heating  may  be  effected  with  the  charcoal  combustion 
furnace,  but  a  gas  furnace  is  most  convenient. 

Fig.  86  represents  the  manner  in  which  the  several  requisite 
pieces  of  apparatus  are  arranged  and  connected.  The  combustion 
tube  rests  in  a  gutter  of  sheet  iron,  but  the  glass  is  kept  from 
contact  with  the  metal  by  a  layer  of  asbestos.  It  is  well  to  secure 
the  tube  to  the  gutter  by  binding  it  with  copper  wire.  At  its 
anterior  end  the  combustion  tube  is  connected  in  the  usual  manner 
with  the  absorbing  apparatus,  consisting  of  a  calcium  chloride  tube, 
potash  bulb,  and  additional  absorbing  tube.  To  the  latter,  which 
is  prepared  as  described  in  §  175,  p.  619,  must  also  be  attached  an 
unweighed  calcium  chloride  tube  to  prevent  moist  air  from  enter- 
ing during  the  process.  B  is  a  bell  jar  standing  in  open  vessel. 
By  opening  the  stop-cock  in  the  tube  which  enters  the  top  of  the 
bell  jar,  the  pressure  within  the  combustion  tube  caused  by  the 
liquid  in  the  potash  bulb  may  be  removed ;  provided  the  water 
levels  within  and  without  the  bell  are  properly  adjusted.  (This 
arrangement  for  relieving  the  pressure  within  the  combustion 
tube  is,  however,  usually  quite  unnecessary.)  It  is  hardly  neces- 
sary to  state  that  any  or  even  all  of  the  several  parts  of  the 
apparatus  here  represented  may  be  replaced  by  other  forms.  An 
ERLENMEYER  combustion  furnace  80  cm.  long,  with  25  burners,  is 
quite  satisfactory.  Many  forms  of  apparatus  have  been  devised 
for  drying  and  purifying  the  air  and  oxygen  which  are  used  in  the 
process.  Fig.  87  shows  one  which  is  durable  and  efficient.  The 
bulb  tube  entering  the  bottle  d  is  connected  with  the  gasometer  by 
means  of  a  rubber  tube.  The  bottle  d  is  half  filled  with  concen- 
trated sulphuric  acid,  through  which  the  gas  or  air  passes  in 
bubbles  and  enters  the  bottom  of  the  cylinder  c.  The  lower  half 
of  this  cylinder  is  filled  with  fragments  of  fused  potash  ;  the  upper 
half  with  calcium  chloride,  which  is  separated  from  the  potash  by  a 
layer  of  asbestos.  Glass  tubes  provided  with  glass  stopcocks  enter 
top  of  each  cylinder  through  rubber  stoppers,  and  are  connected 


§  178.]  ORGANIC  ANALYSIS.  623 

by  means  of  strong  rubber  tubes  to  the  two  limbs  of  the  forked 
tube  J,  so  that  a  regulated  current  of  either  air  or  oxygen  can  be 
made  to  enter  the  combustion  tube  through  a  at  will. 

In  carrying  out  the  process,  the  substance  to  be  analyzed  may 
be  mixed  directly  with  the  oxide  of  copper,  or  it  may  be  placed  in 
a  porcelain  or  platinum  tray  and  kept  out  of  contact  with  the 
oxide.  The  latter  mode  of  proceeding  affords  an  opportunity  for 
obtaining  inorganic  constituents — e.g.,  ashes  in  coal — at  the  same 
time,  and  for  this  and  other  reasons  is  oftenest  preferable,  and  will 
be  first  described  under  a. 

a.  Combustion  in  a  platinum  or  porcelain  tray.  The  combus- 
tion tube  should  be  about  85  cm.  in  length  and  open  at  both  ends. 
Fix  a  plug  of  asbestos,  or  better  fine  copper  gauze,  at  a  point  40 
cm.  from  the  rear  end  of  the  tube,  and  fill  with  coarsely  granulated 
oxide  of  copper  up  to  within  16  cm.  of  the  front  end,  and  secure 
the  oxide  in  place  by  another  plug  of  copper  gauze,  thus  leaving 
about  15  cm.  at  the  front  end  free.  Into  this  space,  a  roll  of 
copper  gauze,  8  to  10  cin.  long,  is  pushed  up  to  the  oxide.  This 
copper  roll  should  be  in  the  metallic  state  if  the  substance  to  be 
analyzed  contains  nitrogen,  chlorine,  or  bromine ;  otherwise  it 
should  previously  be  superficially  oxidized  by  passing  air  or 
oxygen  over  it  in  -a  tube  at  a  red  heat.  Provide  another  similar 
copper  roll  (metallic  for  all  cases)  to  be  placed  behind  the  tray 
containing  the  substance,  next  connect  an  unweighed  calcium 
chloride  tube  to  the  front  end  of  the  combustion  tube,  and  fit  a 
cork  or  rubber  stopper,  through  which  passes  a  small  strong  glass 
tube,  closely  into  the  rear  end. 

Now,  in  order  to  thoroughly  expel  all  hygroscopic  moisture 
from  the  copper  rolls  and  the  oxide,  place  the  combustion  tube  in 
the  furnace,  and  connect  the  tube  inserted  in  the  rear  end  with  the 
tube  #,  fig.  87,  of  the  drying  and  purifying  apparatus,  which  must 
stand  at  the  end  of  the  furnace  connected  with  two  gasometers, 
one  holding  air,  the  other  oxygen  prepared  as  directed  in  §  66,  3. 
The  contents  of  the  tube  are  then  brought  gradually  to  a  dull  red 
heat,  while  a  slow  current  of  dry  air  is  passed  through  it.  Next, 
after  allowing  the  whole  to  cool,  remove  the  stopper  from  the  rear 
end,  draw  out  the  copper  roll  with  a  piece  of  wire,  introduce  the 
weighed  substance  in  a  tray,  pushing  it  nearly  up  to  the  oxide, 
replace  immediately  the  copper  roll,  leaving  it  midway  between  the 
tray  and  the  end  of  the  tube,  replace  also  without  delay  the 


624 


ORGANIC   ANALYSIS. 


[§  178. 


§  178.] 


ORGANIC    ANALYSIS. 


625 


stopper,  and  connect  as  before  with  the  drying  apparatus.  The 
un  weighed  calcium  chloride  tube  is  now  removed  from  the  front 
end  of  the  combustion  tube,  and  the  weighed  absorbing  apparatus 
is  attached.  All  being  thus  made  ready,  with  stopcocks  both  for 
air  and  oxygen  closed,  heat  the  front  roll  of  copper  and  oxide  of 
copper,  so  far  as  possible  without  affecting  the  substance  in  the 
tray,  and  also  the  rear  copper  roll,  all  to  dull  redness.  Then  turn 
on  a  very  slow  current  of  oxygen  and  commence  cautiously  to  heat 
the  tray.  The  oxygen  is  not  designed  to  aid  the  combustion  at  this 


Fig.  87. 

stage :  it  is  taken  up  by  the  metallic  copper ;  but  serves  to  prevent 
products  of  distillation  from  receding  and  being  deposited  in  the 
end  of  the  tube.  The  heat  which  the  substance  itself  will  bear,  or 
the  rate  at  which  the  heat  may  be  increased,  depends  upon  its 
volatility,  and  is  best  regulated  by  observing  the  rate  at  which  gas 
bubbles  enter  the  first  bulb  of  the  potash  apparatus.  When  the 
evolution  of  gas  is  much  diminished  and  only  fixed  carbon  remains 
in  the  tray,  the  rear  copper  roll  is  allowed  to  cool,  and  the  com- 
bustion is  completed  by  increasing  the  current  of  oxygen.  When 
this  is  effected,  and  it  is  observed  that  the  greater  part  of  the 


626  ORGANIC   ANALYSIS.  [§  178. 

reduced  copper  before  the  tray  lias  been  reoxidized,  shut  off  the 
oxygen  and  supply  instead  a  current  of  air  until  the  oxygen  is 
expelled  from  the  apparatus.  The  operation  is  now  at  an  end. 
The  stopcock  admitting  air  is  shut,  and  the  furnace  allowed  to  cool. 

Several  combustions  can  usually  be  made  in  the  same  tube  by 
this  method.  If  the  rear  roll  of  copper  becomes  too  much  oxidized 
by  repeated  use,  it  may  be  reduced  to  the  metallic  state  by  heating 
in  a  current  of  hydrogen.  The  oxide  of  copper  and  the  front 
copper  roll  will  remain  in  order,  unless  it  is  desired  to  have  the 
front  roll  in  the  metallic  state  for  substances  containing  nitrogen, 
&c.,  in  which  case  it  may  also  be  deoxidized  by  hydrogen.  If  one 
combustion  is  to  be  made  immediately  after  another  in  the  same 
tube,  the  preliminary  heating  to  expel  hygroscopic  moisture  is,  of 
course,  unnecessary. 

J.  Combustion  of  the  substance  mixed  with  oxide  of  copper. 
The  combustion  tube  is  prepared  and  ignited  to  expel  hygroscopic 
moisture  from  its  contents  as  above  described  in  <z,  in  all  particulars 
except  the  following :  It  may  be  somewhat  shorter — the  rear  copper 
roll  is  omitted,  a  few  cm.  of  the  rear  portion  of  the  copper  oxide 
should  be  in  a  fine  state  of  division  instead  of  coarsely  granulated. 
After  the  preliminary  ignition  and  sufficient  cooling,  the  tube  is 
taken  from  the  furnace,  and  the  substance  is  introduced  from  the 
long  narrow  tube  in  which  it  has  been  weighed,  and  quickly  i nixed 
with  the  oxide  by  means  of  a  copper  wire  with  twisted  end  (see 
fig.  78,  §  174) ;  next,  without  delay,  oxide  of  copper  which  has 
been  ignited  and  cooled  in  a  tube  or  flask  (see  fig.  77,  §  174)  is. 
poured  into  the  rear  end  of  the  tube — enough  to  occupy  about  12 
cm.  in  length  of  the  space  behind  the  mixture — while  about  an 
equal  space  at  the  very  end  should  remain  empty.  A  few  gentle 
taps  on  the.  table  by  the  tube  in  a  horizontal  position  will  serve  to 
shake  the  contents  down  a  little,  so  as  to  leave  a  narrow  clear 
passage  above.  The  tube 'is  now  laid  in  the  furnace,  the  unweighed 
calcium  chloride  tube  is  removed  from  the  front  end,  the  proper 
absorbing  apparatus  is  attached,  connection  of  the  after-end  with 
the  drying  and  purifying  apparatus  is  made,  and  finally  the  whole 
remaining  part  of  the  process  is  conducted  as  directed  above  in  a, 
except  that  a  very  slow  stream  of  oxygen  may  be  used  at  an  earlier 
stage  of  the  process,  or  at  least  before  signs  of  moisture  or  receding 
gases  appear  in  the  empty  space  at  the  rear  end  of  the  combustion 
tube. 


§  180.] 


ORGANIC   ANALYSIS. 


627 


The  combustion  tube  may  be  used  a  second  time,  or  so  long  as 
it  remains  uninjured,  removing  the  fine  oxide  of  copper  from  the 
after-part  with  a  wire  each  time,  and  allowing  the  granulated  to 


remain. 


IB 


Volatile  Substances,  or  Bodies  undergoing  Alteration  at 
100°  (Losing  Water,  for  instance). 

§  179. 

The  process  is  conducted  either  according  to 
§  174,  or  as  directed  §  178.  Ignited  chromate  of 
lead,  cooled  in  a  closed  tube,  may  also  be  em- 
ployed as  oxidizing  agent. 

b.  FLUID  BODIES. 

a.  Volatile  liquids  (e.g.,  ethereal  oils,  alco- 
hol, etc.). 


Fig.  88. 


§  180. 

1.  The  analysis  of  organic  volatile  fluids  re- 
quires the  objects  enumerated  in  §  174.  The 
combustion  tube  should  be  somewhat  longer  than 
there  mentioned ;  it  should  have  a  length  of  50 
or  60  cm.,  according  as  the  substance  is  less  or 
more  volatile.  The  process  requires  besides  sev- 
eral small  glass  bulbs  for  the  reception  of  the 
liquid  to  be  analyzed.  These  bulbs  are  made  in 
the  following  manner : 

A  glass  tube,  about  30  cm.  long  and  about  8 
mm.  wide,  is  drawn  out  as  shown  in  fig.  88,  fused 
off  at  d,  and  A  expanded  into  a  bulb,  as  shown 
in  fig.  89.  The  bulbed  part  is  then  cut  off  at  ft.  Fig'  89~ 
Another  bulb  is  then  made  in  the  same  way,  and  a  third 
and  fourth,  &c.,  as  long  as  sufficient  length  of  tube  is 
left  to  secure  the  bulb  from  being  reached  by  the  moist- 
ure of  the  mouth. 

Two  of  these  bulbs  are  accurately  weighed ;  they  are 
then  filled  with  the  liquid  to  be  analyzed,  closed  by 
fusion,  and  weighed  again.  The  filling  is  effected  by 


slightly  heating  the  bulb  over  a  lamp  and  immersing  the  point 


628  ORGANIC   ANALYSIS.  [§  180. 

into  the  liquid  to  be  analyzed,  part  of  which,  will  now,  upon  cool- 
ing, enter  the  bulb.  If  the  fluid  is  highly  volatile,  the  portion 
entering  the  still  warm  bulb  is  converted  into  vapor,  which  expels 
the  fluid  again;  but  the  moment  the  vapor  is  recondensed,  the 
bulb  fills  the  more  completely.  If  the  liquid  is  of  a  less  volatile 
nature,  a  small  portion  only  will  enter  at  first ;  in  such  cases  the 
bulb  is  heated  again,  to  convert  what  has,  entered  into  vapor,  and 
the  point  is  then  again  immersed  into  the  fluid,  which  will  now 
readily  enter  and  fill  the  bulb.  The  excess  of  fluid  is  ejected  from 
the  neck  of  the  little  tube  by  a  sudden  jerk ;  the  point  of  the 
capillary  neck  is  then  sealed  in  the  blowpipe  flame.  The  combus- 
tion tube  is  now  prepared  for  the  process  by  introducing  into  it 
from  the  filling-tube  or  flask  (§  174)  a  layer  of  oxide  of  copper 
occupying  about  6  cm.  in  length.  The  middle  of  the  neck  of  one 
of  the  bulbs  is  slightly  scratched  with  a  file,  the  pointed  end  is 
quickly  broken  off,  and  the  bulb  and  end  are  dropped  into  the 
combustion  tube  (see  fig.  90).  Another  layer  of  oxide  of  copper, 
about  6 — 9  cm.  long,  is  then  filled  in,  and  the  other 
bulb  introduced  in  the  same  manner  as  the  first. 
The  tube  is  finally  nearly  filled  with  oxide  .of  cop- 
per. A  few  gentle  taps  upon  the  table  suffice  to 
clear  a  free  passage  for  the  gases  evolved.  (It  is 
advisable  to  place  in  the  anterior  half  of  the  com- 
bustion tube  small  lumps  of  oxide  of  copper  [comp. 
§  66,  1],  or  superficially  oxidized  copper  turnings, 
which  will  permit  the  free  passage  of  the  gases, 
even  with  a  narrow  channel,  or  no  channel  at  all ; 
since  with  a  wide  channel  there  is  the  risk  of  vapors 
passing  unconsumed  through  the  tube.) 

The  combustion  of  highly  volatile  substances 
demands  great  care,  and  requires  certain  modifica- 
tions of  the  common  method.  The  operation  com- 
mences  by  heating  to  redness  the  anterior  half  of 
the  tube,  which  is  separated  from  the  rest  by  a 
screen,  or  in  the  case  of  highly  volatile  substances,  by  two  screens ; 
ignited  charcoal  is  then  placed  behind  the  tube  to  heat  the  tail 
and  prevent  the  condensation  of  vapor  in  that  part.  A  piece  of 
red-hot  charcoal  is  now  applied  to  that  part  of  the  tube  which  is 
occupied  by  the  first  'bulb  ;  this  causes  the  efflux  and  evaporation 
of  the  contents  of  the.  latter ;  the  vapor  passing  over  the  oxide  of 


§  180.]  ORGANIC   ANALYSIS. 

copper  suffers  combustion,  and  thus  the  evolution  of  gas  com- 
mences, which  is  then  maintained  by  heating  very  gradually  the 
first,  and  after  this  the  second  bulb ;  it  is  better  to  conduct  the 
operation  too  slowly  than  too  quickly.  Sudden  heating  of  the 
bulbs  would  at  once  cause  such  an  impetuous  rush  of  gas  as  to 
eject  the  fluid  from  the  potash  bulbs.  The  tube  is  finally  in  its 
entire  length  surrounded  with  ignited  charcoal,  and  the  rest  of  the 
operation  conducted  in  the  usual  way.  If  the  air  drawn  through 
the  apparatus  tastes  of  the  analyzed  substance,  this  is  a  sure  sign 
that  complete  combustion  has  not  been  effected. 

.  2.  In  the  combustion  of  liquids  of  high  boiling  point  and 
abounding  in  carbon,  e.g.,  ethereal  oils,  unconsunied  carbon  is  apt 
to  deposit  on  the  completely  reduced  copper  near  the  substance ; 
it  is  therefore  advisable  to  distribute  the  quantity  intended  for 
analysis  (about  O'-A  grm.)  in  3  bulbs,  separated  from  each  other  in 
the  tube  by  layers  of  oxide  of  copper. 

3.  In  the  combustion  of  less  volatile  liquids,  it  is  advisable  to 
empty  the  bulbs  of  their  contents  before  the  combustion  begins : 
this  is  effected  by  connecting  the  filled  tube  with  an  exhausting 
syringe,  and  rarefying  the  air  in  the  tube  by  a  single  pull  of  the 
handle ;  this  will  suffice  to  expand  the  air-bubble  in  each  bulb  suf- 
ficiently to  eject  the  oily  liquid  from  it,  which  is  then  absorbed  by 
the  oxide  of  copper. 

4.  If  there  is  reason  to  apprehend  that  the  oxide  of  copper 
may  not  suffice  to  effect  the  complete  combustion  of  the  carbon, 
the  process  is  terminated  in  a  stream  of  oxygen  gas  (compare  §  176). 

5.  If  it  is  intended  to  effect  the  combustion  in  the  apparatus 
described  in  §  178  (in  a  current  of  oxygen  gas),  the  bulb  must  be 
drawn  out  to  a  fine  long  point,  and  filled  almost  completely  with 
the  fluid.     The  point  is  then  sealed  in  the  blowpipe  flame,  and  the 
bulbs  are  transferred  in  that  state  to  the  combustion  tube.     When 
the  anterior  and  the  farther  end  of  the  tube  are  red-hot,  a  piece  of 
ignited  charcoal  is  put  to  the  part  occupied  by  the  first  bulb,  when 
the  expansion  of  the  liquid  will  cause  it  to  burst.     When  the  con- 
tents of  the  first  bulb  are  consumed,  the  second,  and  after  this  the 
third,  are  treated  in  the  same  way.     This  method  will  not  answer, 
however,  for  very  volatile  liquids,  as,  e.g.,  ether,  on  account  of  the 
explosion  which  would  inevitably  take  place. 


630  ORGANIC   ANALYSIS.  [§  181. 

fi.  Non-volatile  Liquids  (e.g.,  fatty  oils). 

§  181. 

The  combustion  of  non-volatile  liquids  is  effected  either,  1,  with 
chromate  of  lead,  or  oxide  of  copper  and  oxygen ;  2,  in  the  appar- 
atus described  §  178. 

1.  The  operation  is  conducted  in  general  as  directed  §  175  or 
§  176.  The  substance  is  weighed  in  a  small  tube,  placed  for  that 
purpose  in  a  tin  foot  (see  fig.  91),  and  the  mixing 
effected  as  follows :  Introduce  into  the  combustion 
tube  first  a  layer,  about  6  eni.  long,  of  chromate  of 
lead,  or  of  oxide  of  copper;  then  drop  in  the  small 
cylinder  with  the  substance,  and  let  the  oil  completely 
run  out  into  the  tube  ;  make  it  spread  about  in  various 
Fig.  91.  directions,  taking  care,  however,  to  leave  the  upper 
side  (intended  for  the  channel)  and  the  forepart,  to  the  extent  of  \ 
or  \  of  the  length  of  the  tube,  entirely  clean.  Fill  the  tube  now 
nearly  with  chromate  of  lead  or  oxide  of  copper — which  has  pre- 
viously been  cooled  in  the  filling  tube  or  flask — taking  care  that 
the  little  cylinder  which  contained  the  oil  be  completely  filled  with 
the  oxidizing  agent.  Place  the  tube  in  hot  sand,  which,  imparting 
a  high  degree  of  fluidity  to  the  oil,  leads  to  the  perfect  absorption 
of  the  latter  by  the  oxidizing  agent,  and  proceed  with  the  combus- 
tion in  the  usual  way.  It  is  advisable  to  select  a  tolerably  long 
tube.  Chromate  of  lead  is  usually  to  be  preferred.  If  it  is  used, 
a  very  intense  heat,  sufficiently  strong  to  fuse  the  contents  of  the 
tube,  is  cautiously  applied  in  the  last  stage  of  the  process. 

Solid  fats  or  waxy  substances  which,  not  being  reducible  to 
powder,  cannot  be  mixed  with  the  oxidizing  agent  in  the  usual 
way,  are  treated  in  a  similar  manner  to  fatty  oils.  They  are  fused 
in  a  small  weighed  glass  boat,  made  of  a  tube  divided  lengthwise ; 
when  cold,  the  little  boat  with  its  contents  is  weighed,  and  then 
dropped  into  the  combustion  tube,  which  has  been  previously  filled 
to  the  extent  of  about  6  cm.  with  chromate  of  lead,  or  with  oxide 
of  copper.  The  substance  is  then  fused  by  the  application  of  heat, 
and  made  to  spread  about  in  the  tube  in  the  same  manner  as  is 
done  with  fatty  oils  ;  the  rest  of  the  operation  also  being  conducted 
exactly  as  in  the  latter  case.  If  chromate  of  lead  is  employed,  it 
will  be  found  advantageous  to  add  some  potassium  dichromate 


§  182.]  ORGANIC   ANALYSIS.  631 

(§  177).  If  oxide  of  copper  be  used,  finish  in  a  stream  of  oxygen 
(§  176). 

2.  If  it  is  intended  to  effect  the  combustion  of  fatty  substances 
or  other  bodies  of  the  kind  in  a  tray,  in  a  current  of  oxygen  gas, 
by  means  of  the  apparatus  described  in  §  178,  the  combustion  must 
be  conducted  with  great  care.  As  soon  as  the  oxide  of  copper  in 
the  anterior  and  the  copper  roll  in  the  posterior  parts  of  the  tube 
are  red-hot,  carefully  regulated  heat  is  applied  to  the  part  occupied 
by  the  tray.  The  volatile  products  generated  by  the  dry  distilla- 
tion of  the  substance  burn  at  the  expense  of  the  oxide  of  copper. 

When  it  is  perceived  that  the  surface  layer  of  the  oxide  of  cop- 
per is  reduced,  the  application  of  heat  to  the  substance  is  suspended 
for  a  time,  and  resumed  only  after  the  reduced  copper  is  reoxid- 
ized  in  the  stream  of  oxygen  gas.  Care  is  finally  taken  to  insure 
the  complete  combustion  of  the  carbon  remaining  in  the  boat. 


Supplement  to  A.,  §§  174—181. 

§182. 
MODIFIED  APPARATUS  FOB  THE  ABSORPTION  OF  CARBONIC  ACID. 

G.  J.  MULDER*  has  replaced  the  potash  bulbs  altogether  by  a 
totally  different  absorption  apparatus.  The  calcium  chloride 
tube  is  immediately  connected  with  the  system  of  U-tubes,  fig. 
92 ;  a  contains  small  pieces  of  glass,  6  to  10  drops  concentrated 
sulphuric  acid,  and  at  the  top 
asbestos  plugs.  J  is  filled  to  -J 
with  granulated  soda  lime  (say 
20  grm.  prepared  as  directed 
in  §  66,  4),  the  remaining  -J  (in 
the  2d  limb)  contains  calcium 
chloride  (say  3  grm.).  Lastly,  c 
is  filled  with  lumps  of  potassa. 
a  and  b  are  weighed  together, 
c  serves  as  a  guard  to  5,  and 
is  not  weighed.  The  sulphuric 
acid  tube  serves  to  show  the  Fig-  92. 

rate  of  the  evolution  of  gas ;  it  contains  enough  sulphuric  acid, 

*  Zeitschrift  f.  analyt.  Chem.  1,  2. 


632  OKGANIC   ANALYSIS.  [§  182. 

"when  the  lower  part  is  just  stopped  up.  If  the  process  goes 
on  properly,  the  weight  of  the  tube  does  not  increase  more  than 
1  ingrni. ;  generally  the  increment  is  unweighable.  If  the  tube 
is  closed  after  use  with  caoutchouc  caps,  it  may  be  used  over 
and  over  again.  The  sulphuric  acid  possesses  the  advantage  over 
other  fluids  that  it  indicates  whether  the  combustion  was  complete 
or  not ;  for  in  the  first  case  it  remains  colorless,  in  the  second 
it  becomes  brown  from  the  escaping  hydrocarbons,  and  then  the 
results  cannot  be  expected  to  be  perfectly  accurate.  The  absorp- 
tion of  the  carbonic  acid  by  the  soda-lime  tube  is  as  rapid  as  it  is 
complete ;  even  when  a  stream  of  carbonic  acid  is  passing,  with 
ten  times  the  rapidity  usual  in  organic  analysis,. no  trace  of  the 
acid  makes  its  escape.  The  absorption  of  the  carbonic  acid  is 
attended  with  warming  of  the  soda-lime ;  if  any  water  evaporates 
from  the  soda-lime,  it  is  retained  by  the  calcium  chloride  in  the 
second  limb.  The  corks  of  the  absorption  tubes  are,  like  the  others, 
coated  with  sealing-wax.  A  filled  soda-lime  tube  weighs  about  40 
grin.  The  first  time  it  is  used  alone ;  the  second  time  the  same 
tube  is  used,  but  as  a  precautionary  measure  a  second  similarly 
filled  and  separately  weighed  tube  is  placed  in  front  of  it.  The 
second  tube  rarely  increases  in  weight,  and  unless  it  does,  the  first 
tube  can  be  used  a  third  time,  but  of  course  in  connection  with  the 
second.  If  the  second  tube  has  gained  in  the  third  operation,  the 
first  tube  is  rejected  at  the  fourth  operation,  and  the  second  is  now 
used  alone,  &c.  If  after  the  combustion  a  stream  of  oxygen  is 
transmitted  through  the  combustion  tube,  the  tubes  are  of  course 
at  the  end  full  of  oxygen.  If,  then,  care  be  taken  that  the  tubes 
are  full  of  oxygen  before  weighing,  the  trouble  of  the  final  trans- 
mission of  air  may  be  saved.  For  weighing,  MULDER  closes  the 
ends  of  the  glass  tubes  with  caps  made  out  of  india-rubber  tube. 
According  to  DIBBITS,*  however,  this  is  not  to  be  recommended. 

MULDER'S  absorption  apparatus  is  peculiarly  suitable,  when  the 
carbonic  acid  is  mixed  with  another  gas.  It  insures  complete 
absorption,  precludes  the  evaporation  of  any  water,  and  offers  per- 
fect security  in  case  of  the  sudden  occurrence  of  a  too  rapid  evolu- 
tion of  gas. 


3eit.  f.  anal.  Chem.  15,  157. 


§  183.]  ORGANIC   ANALYSIS.  633 

B.  ANALYSIS  OF  COMPOUNDS  CONSISTING  OF  CARBON,  HYDROGEN, 
OXYGEN,  AND  NITROGEN. 

The  principle  of  the  analysis  of  such  compounds  is  in  general 
this:  in  one  portion  the  carbon  and  the  hydrogen  are  determined 
as  carbonic  acid  and  water  respectively ;  in  another  portion,  the 
nitrogen  is  determined  either  in  the  gaseous  form,  or  as  ammonium 
platinic  chloride,  or  by  determining  volumetrically  the  ammonia 
formed  from  the  nitrogen ;  the  oxygen  is  calculated  from  the  loss. 

As  the  presence  of  nitrogen  exercises  a  certain  influence  upon 
the  estimation  of  carbon  and  hydrogen,  we  have  here  to  consider 
not  only  the  method  of  determining  the  nitrogen,  but  also  the 
modifications  which  the  presence  of  the  nitrogen  renders  necessary 
in  the  usual  method  of  determining  the  carbon  and  hydrogen. 


a.  DETERMINATION  OF  THE  CARBON  AND  HYDROGEN  IN  NITROGENOUS 

SUBSTAN(  •]->. 

§  183. 

.  1.  When  nitrogenous  substances  are  ignited  with  oxide  of  cop- 
per or  with  lead  chromate,  a  portion  of  the  nitrogen  present 
escapes  in  the  gaseous  form,  together  with  the  carbonic  acid  and 
aqueous  vapor;  whilst  another  portion,  minute  indeed,  still,  in 
bodies  abounding  in  oxygen,  not  quite  insignificant,  is  converted 
into  nitric  oxide  gas,  which  is  subsequently  transformed  wholly  or 
partially  into  nitrous  acid  by  the  air  in  the  apparatus.  The  appli- 
cation of  the  methods  described  in  §§  174,  etc.,  in  the  analysis  of 
nitrogenous  substances  would  accordingly  give  too  much  carbon  ; 
since  the  potash  bulbs  would  retain,  besides  the  carbonic  acid,  also 
the  nitrous  acid  formed  and  a  portion  of  the  nitric  oxide  (which  in 
the  presence  of  potassa  decomposes  slowly  into  nitrous  acid  and 
nitrous  oxide).  This  defect  may  be  remedied  by  selecting  a  com- 
bustion tube  about  12 — 15  cm.  longer  than  those  commonly 
employed,  filling  this  in  the  usual  way,  but  finishing  with  a  loose 
layer,  about  9 — 12  cm.  long,  of  clean,  fine  copper  turnings  (§  66, 
6),  or  a  compact  roll  of  copper  wire-gauze.  The  roll  of  copper 
gauze  in  front  of  the  oxide  should  not  be  previously  oxidized  (as 
is  recommended  for  substances  free  from  nitrogen  chlorine  and 


634  ORGANIC   ANALYSIS.  [§  183. 

bromine),  but  should  be  in  the  metallic  state*.  The  process  is  com- 
menced by  heating  these  copper  turnings  to  redness,  in  which  state 
they  are  maintained  during  the  whole  course  of  the  operation. 
These  are  the  only  modifications  required  to  adapt  the  methods 
above  described  for  the  analysis  of  nitrogenous  substances.  The 
use  of  the  metallic  copper  depends  upon  its  property  of  decompos- 
ing, when  in  a  state  of  intense  ignition,  all  the  oxides  of  nitrogen 
into  oxygen,  with  which  it  combines,  and  into  pure  nitrogen  gas. 
As  the  metal  exercises  this  action  only  when  in  a  state  of  intense 
ignition,  care  must  be  taken  to  maintain  the  anterior  part  of  the 
tube  in  that  state  throughout  the  process.  As  metallic  copper 
recently  reduced  retains  hydrogen  gas,  and,  when  kept  for  some 
time,  aqueous  vapor  condensed  on  the  surface,  the  copper  turnings 
intended  for  the  process  must  be  introduced  into  the  tube  hot  as 
they  come  from  the  drying  closet  (which  is  heated  to  100°).  v. 
LIEBIG  recommends  to  compress  the  hot  turnings  in  a  tube  into  a 
cylindrical  form,  to  facilitate  their  rapid  introduction  into  the 
combustion  tube. 

2.  If  it  is  intended  to  burn  nitrogenous  bodies  in  the  apparatus 
described  in  §  178,  care  must  be  taken  to  keep  at  least  the  anterior 
half  of  the  roll  from  oxidizing,  both  during  the  ignition  in  the 
current  of  air  and  during  the  actual  process  of  combustion.    When 
the  operation  is  terminated,  and   the    oxidation   of   the  metallic 
copper  is  visibly  progressing,  the  oxygen  is  turned  off,  and  the 
cock  of  the  air  gasometer  opened  a  little  instead,  to  let  the  tube 
cool  in  a  slow  stream  of  atmospheric  air. 

3.  Since  the  metallic  copper  is  usually  oxidized  during  each 
combustion  and  must  be  reduced  again,  STEmf  uses  silver  instead 
of  copper.     Silver  has  the  additional  advantage  that  it  retains  also 
chlorine.     According  to  the  investigations  of  CALBERLA,  silver  at  a 
red  heat  reduces  oxides  of  nitrogen  completely,  while  it  does  not 
exercise  the  least  influence  on  carbonic  acid. 

b.    DETERMINATION  OF  THE  NITROGEN  IN  ORGANIC  COM- 
POUNDS. 
As  already  indicated,  two  essentially  different  methods  are  in 

*  The  copper  turnings  or  gauze  cannot  be  replaced  by  the  metallic  powder 
obtained  by  the  reduction  of  the  oxide  with  hydrogen,  as  this  obstinately  retains 
hydrogen,  and  consequently  decomposes  appreciable  quantities  of  carbonic  acid 
with  formation  of  carbonic  oxide.  Schr5tter,  Lautemann,  Journ.  f.  prakt. 
Chem.  77,  316. 

f  Zeitschrift  f.  anal.  Chem.  8,  83. 


§  184. J  ORGANIC   ANALYSIS.  635 

use  for  effecting  the  determination  of  the  nitrogen  in  organic  com- 
pounds ;  viz.,  the  nitrogen  is  either  separated  in  the  pure  form  and 
its  volume  measured,  or  it  is  converted  into  ammonia,  and  this  is 
determined  either  as  ammonium  platinic  chloride,  or  volumetric- 
ally  by  neutralization. 


a.  Determination  of  the  Nitrogen  from  the  Volume. 
§184. 

aa.  DUMAS'  Method,  modified  by  Schiel. 

This  method  may  be  employed  in  the  analysis  of  all  organic 
compounds  containing  nitrogen.  It  requires  a  graduated  glass 
cylinder  of  about  200  c.c.  capacity,  with  a  ground-glass  plate  to 
<x>ver  it. 

The  combustion  tube  should  be  60  or  70  cm.  long,  and  drawn 
out  at  the  posterior  end  to  a  stout  open  tail,  which  should  have  a 
small  bulb  or  swell  for  the  better  fastening  of  a  rubber  tube  to  it. 
Introduce  into  it  near  the  tail  a  plug  of  newly  ignited  asbestos, 


Fig.  93 

then  a  layer  of  oxide  of  copper,  4  cm.  long ;  after  this  the  intimate 
mixture  of  an  accurately  weighed  portion  of  the  substance  (0*3 — 
0*6  grm.,  or,  in  the  case  of  compounds  poor  in  nitrogen,  a  some- 
what larger  quantity)  with  oxide  of  copper,  then  the  oxide  which 
lias  served  to  rinse  the  mortar,  followed  by  a  layer  of  pure  oxide, 
and,  lastly,  a  layer  of  copper  turnings,  about  15  cm.  long.  Make 
a  channel  along  the  top  of  the  tube  by  gentle  tapping.  Connect 
the  tube  with  the  bent  delivery  tube  cf  (fig.  93),  and  place  in  the 
furnace.  Connect  the  tail  by  means  of  a  stout  tube  of  india-rub- 
ber with  an  apparatus  for  giving  a  continuous  stream  of  washed 
carbonic  acid  gas.  Transmit  this  slowly  through  the  tube  for  half 
an  hour,  then  immerse  the  end  of  the  bent  delivery  tube  under 
mercury,  and  invert  over  it  a  test  tube  filled  with  solution  of 


636  ORGANIC    ANALYSIS.  [§  184. 

potassa.  If  the  gas  bubbles  entering  the  cylinder  are  completely 
absorbed  by  the  solution  of  potassa,  this  is  a  proof  that  the  air  is 
thoroughly  expelled  from  the  tube.  But  should  this  not  be  the 
case,  the  evolution  of  carbonic  acid  must  be  continued  until  the 
desired  point  is  attained.  "When  the  gas  is  completely  absorbed, 
close  the  communication  between  the  CO2  generator  and  the  com. 
bustion  tube  by  a  screw  clamp  or  stopcock,  invert  the  graduated 
cylinder,  filled  -f  with  mercury,  -J  with  concentrated  solution  of 
potassa,  over  the  end  of  the  delivery  tube,  with  the  aid  of  a 
ground-glass  plate,*  and  proceed  with  the  combustion  in  the  usual 
way,  heating  first  the  anterior  end  of  the  tube  to  redness,  and 
advancing  gradually  towards  the  farther  end.  In  the  last  stage  of 
the  process,  communication  is  reestablished  with  the  CO2  genera- 
tor, and  thus  the  whole  of  the  nitrogen  gas  which  still  remains  in 
the  tube  is  forced  into  the  cylinder.  Wait  now  until  the  volume  of 
the  gas  in  the  cylinder  no  longer  decreases,  even  upon  shaking  the 
latter  (consequently,  until  the  wThole  of  the  carbonic  acid  has  been 
absorbed),  then  place  the  cylinder  in  a  large  and  deep  glass  vessel 
filled  with  water,  the  transport  from  the  mercurial  trough  to  this 
vessel  being  effected  by  keeping  the  aperture  closed  with  a  small 
dish  filled  with  mercury.  The  mercury  and  the  solution  of  potassa 
sink  to  the  bottom,  and  are  replaced  by  water.  Immerse  the  cylin- 
der, then  raise  it  again  until  the  water  is  inside  and  outside  on  an 
exact  level ;  read  off  the  volume  of  the  gas  and  mark  the  tempera- 
ture of  the  water  and  the  state  of  the  barometer ;  calculate  the 
weight  of  the  nitrogen  gas  from  its  volume,  after  reduction  to  the 
normal  temperature  and  pressure,  and  with  due  regard  to  the  ten- 
sion of  the  aqueous  vapor  (comp.  "  Calculation  of  Analyses").  The 
results  are  generally  somewhat  too  high,  viz.,  by  about  O2 — 0*5 
per  cent. ;  this  is  owing  to  the  circumstance  that  even  long-con- 
tinued transmission  of  carbonic  acid  through  the  tube  fails  to  expel 
every  trace  of  atmospheric  air  adhering  to  the  oxide  of  copper. 

*  The  following  is  the  best  way  of  filling  the  cylinder  and  inverting  it  over 
the  opening  of  the  bent  delivery  tube : — The  mercury  is  introduced  at  first,  and 
the  air-bubbles  which  adhere  to  the  walls  of  .the  vessel  are  removed  in  the  usual 
way.  The  solution  of  potassa  is  then  poured  in,  leaving  the  top  of  the  cylinder 
free  to  the  extent  of  about  2  lines;  this  is  cautiously  filled  up  to  the  brim  with 
pure  water,  and  the  ground-glass  plate  slided  over  it.  The  cylinder  is  now 
inverted,  and  the  opening  placed  under  the  mercury  in  the  trough ;  the  glass  plate 
is  then  withdrawn  from  under  the  cylinder.  In  this  manner  the  operation  may 
be  performed  easily,  and  without  soiling  the  fingers. 


§  184.]  ORGANIC   ANALYSIS.  637 

It  is  highly  advisable,  before  making  any  nitrogen  determina- 
tions with  this  method,  to  subject  a  non-nitrogenous  substance,  e.g., 
sugar,  to  the  same  process.  The  analyst  thereby  acquaints  himself 
with  the  extent  of  the  error  to  which  he  will  be  exposed.  In  such 
an  experiment  the  quantity  of  unabsorbed  gas  should  not  exceed 
1  or  1£  c.c. 

To  insure  complete  combustion  of  difficultly  combustible  bod- 
ies, STRECKER  recommends  the  addition  of  arsenious  oxide  in  pow- 
der to  the  oxide  of  copper  with  which  the  substance  is  to  be  mixed ; 
the  arsenious  oxide  is  volatilized  by  the  action  of  the  heat,  the 
fumes  burning  the  whole  of  the  carbon  like  a  current  of  oxygen. 
The  arsenious  oxide  sublimes  in  the  anterior  part  of  the  tube, 
arsenic  remains  in  the  copper. 

bb.  By  exhaustion  of  the  combustion  tube  with  an  air  pump, 
ami  measurement  of  nitrogen  in  Schiff^s  Azotometer. 

A  process  capable  of  giving  much  more  accurate  results  than 
the  preceding  (ad)  has  been  developed  by  FRANKLAXD  and  ARM- 
STRONG,* GIBBS  \  and  JOHNSON.  It  is  described  \  as  follows  : 

REAGENTS. 

'Cupric  oxide. — "  Copper  scale,"  which  may  contain  cuprous 
oxide,  coal  dust,'  oil,  &c.,  is  mixed  in  an  iron  pot  with  10  per  cent. 
of  potassium  chlorate  and  enough  water  to  make  a  thin  paste.  The 
mass  is  heated  and  stirred  till  dry,  the  heat  is  then  raised  to  the  point 
of  ignition,  and  until  the  mass  does  not  glow  nor  sparkle  when 
stirred. 

The  potassium  chloride  is  washed  out  by  decantation  and  the 
cupric  oxide  is  dried  and  moderately  ignited. 

Metallic  copper. — Granular  copper  oxide,  or  fine  copper  gauze, 
is  suitable  for  its  preparation.     The  granular  copper  is  most  con-, 
venient ;    copper  gauze  must  be  made  into  rolls  adapted  to  the 
combustion  tube.     The  copper  is  reduced  and  cooled  as  usual  in  a 
stream  of  hydrogen. 

Potassium  chlorate.— Commercial  potassium  chlorate  is  fused 
in  porcelain  and  pulverized. 

Sodium  bicarbonate  must  contain  no  organic  matter. 


*  Jour.  Chem.  Soc.  [ii],  vol.  vi.  p.  77. 

f  Ara.Journ.Sci.  and  Arts,  vol.  xlviii. 

J  By  JOHNSON  and  JENKINS,  American  Chemical  Journal,  ii.  27. 


638 


ORGANIC    ANALYSIS. 


[§  184. 


Solution  of  Caustic  Potash. — Dissolve  commercial  "  stick  pot- 
ash" in  less  than  its  weight  of  water,  making  a  solution  so  concen- 
trated that,  on  cooling,  it  deposits  crystals  of  potassium  hydrate. 

The  same  clear  solution  may  be  used  for  a  number  of  combus- 
tions or  until  the  absorption  of  carbonic  acid  gas  is  not  quite  prompt. 

APPARATUS. 

The  Combustion  tube  should  be  of  the  best  hard  Bohemian 

glass,  about  2  feet  4  inches  long.     The  rear  end  is  bent  and  sealed 

as  in.  fig.  96. 

It  is  best  to  protect  the  horizontal  part  with  thin  copper  foil. 

The  tube  is  connected  with  the  pump  by  a  close  fitting  rubber 

cork,  smeared  with  glycerine. 

Azotometer. — This  is  a  modification  of  the  apparatus  invented 

and  described  by  Schiif,  Fres.  Zeitschrift,  Bd.  7,  p.  430. 
It  is  represented  in  fig.  94. 

The  gas  is  measured  in  an  accurately  calibrated  cylinder  (bu- 
rette) A  of  120  c.  c.  capacity,  graduated  to 
.  fifths  of  cubic  centimetres,  and  closed  at  the 
upper  end  by  a  glass  stopcock.  The  lower 
end  is  connected,  by  means  of  a  perforated 
rubber  stopper  about  1J  inches  long  and 
1^  inches  diameter,  with  another  tube  hav- 
ing two  arms,  one,  D,  to  receive  the  delivery 
tube  from  the  pump,  the  other  connected 
by  a  rubber  tube  with  a  bulb  of  200  c.  c. 
capacity,  F,  through  which  potash  solution 
is  supplied.  The  graduated  tube  is  en- 
closed in  a  water-jacket  with  an  external 
diameter  of  about  If  inches.  Its  lower  end 
is  closed  by  the  caoutchouc  stopper  that 
connects  the  two  parts  of  the  azotometer 
described  above.  The  upper  end  of  the 
jacket  is  closed  by  a  thin  rubber  disc,  slit 
radially  and  having  four  perforations  :  one 
in  the  centre,  through  which  the  neck  of 
the  graduated  tube  passes,  and  three  others 
near  the  circumference. 
Through  one  of  the  latter,  a  glass  tube,  L,  bent  as  in  the  figure, 

reaches  to  the  bottom  of  the  jacket,  another  short  tube  just  passes 


Fig.  94. 


§  184.] 


ORGANIC    ANALYSIS. 


639 


through  the  disc,  and  the  third  hole  is  for  supporting  a  thermo- 
meter. The  azotometer  is  held  upright  and  firm  on  a  stand  by 
rings  fitting  around  the  jacket  and  by  cork  wedges. 

The  bulb  for  potash  solution  rests  in  a  slotted,  sliding  ring. 

The  air  pump  used  is  the  Sprengel  mercury  pump,  modified 
merely  so  as  to  be  easily  constructed  and  durable.  Its  essential 
parts  are  sketched  in  fig.  95.  Some  of  them  are  exaggerated  in 
order  to  show  their  construction  more  plainly.  Through  a  rubber 
stopper  wired  into  the  nozzle  of  the  mercury  reser- 
voir, A,  passes  a  glass  tube,  B,  4  inches  long ;  this 
connects  by  a  caoutchouc  tube  with  the  straight 
tube  D,  3  feet  long.  ^The  rubber  tube  E,  6  inches 
long,  connects  D  with  a  straight  glass  tube,  F,  of 
about  the  same  length  as  D. 

G  is  a  piece  of  combustion  tube  1^  inches  long, 
closed  below  by  a  doubly  perforated  soft  rubber 
stopper  admitting  the  tubes  F  and  H,  and  above  by 
a  singly  perforated  rubber  stopper  into  which  a 
tube,  I,  is  fitted.  The  tube  H  has  a  length  of  45 
inches.  At  the  bottom  it  is  connected  by  rubber 
with  a  straight  tube  of  3  inches,  and  this  again  with 
a  tube,  K,  of  7  inches.  The  tubes  H  K  should 
have  an  internal  diameter  of  1£  millimetres,  F  may 
be  2  millimeters,  and  D  still  larger. 

We  have  used  for  H  and  F  slender  Bohemian 
glass  tubes  of  4  millimetres  exterior  diameter.  Their 
elasticity  compensates  for  their  slenderness.  If 
heavy  barometer  tubes  be  used,  the  stoppers  and  G 
must  be  of  correspondingly  larger  dimensions. 

The  joints  at  G  must  be  made  with  the  great- 
est care. 

It  is  best  to  insert  the  lower  stopper  for  half 
its  length  into  G,  having   the  dimensions  of   the 
parts  so  related  that  it  requires  considerable  effort 
to  force  the   slightly  greased  tubes  F  and  H  to 
their  places  just  through  the  stopper.     The  tube 
I  must  be  of  stout  glass — a  decimetre  in  diameter.     It  is  drawn 
out  at  either  end  to  a  long  taper,  and  bent  as  in  the  figure,  in  order 
to  bring  its  free  extremity  to  the  level  of  the  combustion  furnace. 
The  hole  in  the  upper  rubber  stopper  has  a  diameter  of  5  mm.. 


J| 


640  ORGANIC    ANALYSIS.  [§  184. 

just  sufficient  to  admit  the  narrowed  end  of  the  tube,  which,  after 
greasing  or  moistening  with  glycerine,  is  "  screwed  down"  into  the 
stopper. 

These  three  joints  are  the  only  ones  belonging  to  the  pump 
which  have  to  resist  diminished  pressure,  and  require  .extreme  care 
in  making. 

If  not  entirely  secure  they  are  to  be  trapped  with  glycerine. 
For  this  purpose  it  is  needful  to  pass  F  and  H  through  a  stopper 
of  half  an  inch  greater  diameter  than  G  and  correspondingly 
perforated  before  entering  the  latter.  Then,  previous  to  inserting 
I,  a  tube  4  inches  long  is  slipped  over  G  upon  this  wider  stopper. 
When  I  has  been  inserted  and  the  tubes  have  been  secured  to 
their  support,  the  space  between  G  and  the  outer  tube  is  filled 
with  the  most  concentrated  glycerine,  which  is  prevented  from 
absorbing  moisture  by  corking  above. 

The  two  rubber  tubes  are  both  provided  with  stout  screw 
clamps,  to  admit  of  exactly  regulating  the  flow  of  mercury.  The 
tubes  D,  F,  H,  and  I  are  secured  to  a  vertical  plank  framed  below 
into  a  heavy  horizontal  wooden  foot  on  which  rests  the  mercury 
trough,  and  having  above  a  horizontal  shelf  through  an  aperture 
of  which  passes  the  neck  of  A. 

The  tubes  D,  F,  H,  and  I  are  secured  to  the  plank  at  several 
points  by  wooden  or  cork  clamps,  clasping  the  tubes  and  fastened 
by  screws  or  wires. 

These  fastenings  are  made  elastic  by  the  intervention  of  a  thick 
rubber  tube  between  the  glass  and  wood.  The  connections  C  and 
E  should  be  made  of  stout  vulcanized  rubber,  those  at  the  base  of 
H  K  of  fine  black  rubber. 

The  latter  should  be  soaked  in  melted  tallow  previous  to  use, 
all  excess  being  carefully  removed  from  the  interior.  The  joints 
should  be  wound  with  waxed  silk. 

A  glass  funnel  is  placed  within  A  to  prevent  spattering  of  the 
mercury  when  it  is  filled. 

OPERATION. 

From  3  to  4  grains  of  potassium  chlorate,  according  to  the 
amount  of  carbon  to  be  burned,  are  put  into  the  tail  of  the  com- 
bustion tube,  fig.  96,  followed  by  an  asbestos  plug  just  at  the  bend. 
The,  substance  to  be  analyzed  (O6 — 0*8  grams)  is  well  mixed  in 
a  mortar  with  enough  cupric  oxide  that  has  been  freshly  ignited 


£  184.]  ORGANIC   ANALYSIS.  641 

and  allowed  to  cool  to  make  a  layer  11  or  12  inches  long  in  the 
tube.  The  mixture  is  introduced  through  a  funnel  and  rinsed 
with  enough  cupric  oxide  to  make  a  layer  of  3  inches,  a  second 
asbestos  plug,  and  upon  it  a  layer  of  reduced  copper  of  4  or  5 
inches  long  are  put  in,  then  a  third  asbestos  plug,  then  2  inches  of 
cupric  oxide,  a  fourth  asbestos  plug,  then  -8  to  1'  grams  of  sodium 
bicarbonate.  The  remaining  space  in  the  tube  is  loosely  filled  with 
asbestos,  to  absorb  the  water  which  is  formed  during  combustion, 


MIXTURE         JRlNSINGSj        Cu.     jCuO ;co?  j  ASBESTUS  j 


1 a < 

j 


j  8cm.   \         30cm.          |  8cm.    I   12cm*  iscmlacm!    10cm.    j 

Fig.  96. 

and  prevent  it  from  flowing  back  upon  the  heated  glass.  The 
anterior  part  of  the  tube  containing  the  cupric  oxide  and  reduced 
copper  is  wound  with  copper  foil,  leaving,  however,  a  little  of  the 
copper  (Cu.  in  fig.  96)  visible  at  its  rear.  The  combustion  tube  is 
placed  in  the  furnace  at  the  bend  of  the  tube  I,  and  connected  with 
the  latter  by  a  close-fitting  rubber  stopper  smeared  with  glycerine. 
Care  must  be  taken  to  make  the  joint  perfectly  tight.  The 
combustion  tube  has  its  conical  rubber  stopper  partly  inserted, 
and  is  then  forced  and  rotated  upon  the  tapering  and  stout  end  of 
the  tube  I,  the  latter  being  supported  by  one  hand  applied  at  the 
lower  bend. 

PREPARATION  OF  THE  AZOTOMETER. 

Fill  the  bottom  of  the  azotometer  to  about  the  level  indicated  by 
the  dotted  line  G,  with  mercury.  Close  the  arm  D  securely  with 
a  rubber  stopper.  Grease  the  stop-cock  H  and  insert  the  plug, 
leaving  the  cock  open. 

Pour  potash  solution  into  F  till  A  is  nearly  full,  and  there  is 
still  some  solution  in  the  bulb  F.  Raise  the  bulb  cautiously  with 
one  hand,  holding  the  stop-cock  H  in  the  other  hand.  When  the 
solution  in  A  has  risen  very  nearly  to  the  glass  cock,  close  the  lat- 
ter, avoiding  contact  of  the  alkali  with  the  ground  glass  bearings. 
Replace  the  bulb  in  the  ring  and  lower  it  as  far  as  may  be.  If  the 
level  of  the  solution  in  the  azotometer  does  not  fall  in  15  or  20 
minutes,  it  is  tight.  Place  the  delivery  tube  of  the  pump  K  in  a 
mercury  trough. 


642  ORGANIC   ANALYSIS.  [§  184. 

Supply  the  vessel  A  with  at  least  500  c.  c.  of  mercury.  Cau- 
tiously open  the  clamps  C  and  E.  If  the  mercury  does  not  start  at 
once  pinch  the  rubber  at  E  repeatedly.  The  mercury  should  flow 
nearly  as  fast  as  it  can  be  discharged  at  K,  without  filling  the  cylin- 
der G.  Five  to  ten  Minutes  working  of  the  pump  will  generally 
suffice  to  make  a  complete  exhaustion  of  the  combustion  tube.  If 
most  of  the  mercury  runs  out  before  exhaustion  is  complete,  close- 
the  clamp  C,  return  the  mercury  to  A,  and  repeat  the  operation. 
When  there  is  a  complete  exhaustion,  the  mercury  falls  with  a  rat- 
tling or  clicking  sound.  After  it  has  been  distinctly  heard  for  half 
a  minute,  close  the  clamp  C.  If  the  mercury  column  in  H  remains 
stationary  for  some  minutes,  the  connections  are  proved  to  be 
tight. 

ADJUSTING   THE    AZOTOMETER. 

Remove  the  mercury  trough,  placing  K  in  a  capsule. 

Heat  the  part  of  the  tube  containing  sodium  bicarbonate.  Water 
vapor  and  carbon  dioxide  are  evolved,  which  fill  the  vacuum  in  H 
and  expel  the  mercury.  While  this  is  being  done  place  the  azoto- 
meter  near  by,  remove  the  bulb  F  from  the  ring  and  support  it  in 
a  box  near  the  level  of  D,  so  that  the  stopper  may  be  removed 
from  D  without  greatly  changing  the  level  of  the  mercury  G,  and 
so  that  the  azotometer  can  be  moved  freely  without  disturbing  it. 
When  the  cork  in  D  has  been  removed  fill  D  half  full  or  more 
with  water. 

As  soon  as  the  mercury  has  fully  escaped  from  K  insert  the  lat- 
ter in  D.  Let  a  few  bubbles  escape  through  the  water  and  then 
pass  the  tube  K  down  so  that  the  escaping  gas  enters  the  azotome- 
ter. It  will  much  facilitate  the  delivery  of  gas  if  the  extremity  of 
the  tube  K  just  touches  the  inside  of  the  azotometer  tube,  and  is 
kept,  as  near  as  possible,  to  the  surface  of  the  mercury. 

The  carbon  dioxide  is  absorbed  in  passing  through  the  caustic 
potash  solution.  In  spite  of  all  precautions  very  minute  bubbles  of 
permanent  gas  will  occasionally  ascend,  but,  as  will  be  seen  on 
observing  the  amount  of  potash  solution  thus  displaced,  the  error 
thereby  occasioned  is  extremely  small. 

THE    COMBUSTION. 

First  heat  the  anterior  cupric  oxide  to  full  redness,  and  after- 
wards the  copper.  The  fine  gauze  or  pulverulent  copper  very  com- 


§  184.]  OKGANIC   ANALYSIS.  643 

pletely  reduces  any  oxides  of  nitrogen  which  might  be  produced 
in  the  combustion,  and  also  retains  any  excess  of  oxygen  which  is 
evolved  at  the  close  of  the  process. 

The  anterior  cupric  oxide  burns  the  traces  of  hydrogen  which 
may  be  held  by  the  reduced  copper,  even  when  the  tube  is 
exhausted,  and  also  destroys  the  carbon  monoxide  which  is  usually 
formed  when  steam  and  carbon  dioxide  pass  together  over  reduced 
copper,  if  iron  or  carbon  be  present.  Go  on  with  the  combustion 
as  usual,  bringing  the  heat  up  to  a  fair  redness.  The  flow  of  gas 
may  be  made  quite  rapid,  say  one  bubble  a  second,  or  a  little  faster. 

When  the  horizontal  part  of  the  -tube  has  all  been  heated,  and 
the  evolution  of  gas  has  nearly  ceased,  heat  the  potassium  chlorate 
so  that  it  boils  vigorously  from  evolution  of  oxygen.  The  reoxidiza- 
tion  of  the  reduced  copper  oxide  and  of  any  unburned  carbon  pro- 
ceeds rapidly. 

"When  the  oxygen,  whose  flow  admits  of  easy  regulation,  begins 
to  attack  the  anterior  layer  of  reduced  copper,  stop  its  evolution 
and  lower  the  flames  all  along  the  tube,  keeping  the  reduced  cop- 
per still  faint  red. 

After  a  few  minutes  start  the  pump,  slowly  at  first,  having  some 
vessel  under  the  tube  D  of  the  azotometer  to  receive  the  mercury. 
A  few  minutes  pumping  suffices  to  clear  the  tube.  Remove  the 
azotometer,  close  the  tube  D  with  its  rubber  stopper,  then  raise  the 
bulb  into  its  ring  to  such  a  height  that  the  potash  solution  in  it 
shall  be  at  about  the  same  level  as  that  in  the  graduated  tube.  Con- 
nect L  at  its  upper  end  with  a  water  supply,  insert  a  thermometer 
in  the  top  of  the  water  jacket  and  let  the  water  run,  until  the  tem- 
perature and  the  volume  of  gas  are  constant. 

Read  off  the  volume  of  gas  and  temperature,  after  having  accu- 
rately adjusted  the  level  of  the  solution  in  the  bulb  to  that  in  the 
azotometer. 

Read  the  barometer  and  make  the  calculations  in  the  usual  way. 
When  50  per  cent,  potash  solution  is  used,  no  correction  need  be 
made  for  tension  of  aqueous  vapor,  as  SCHIFF  has  shown. 

The  calculation  is  somewhat  shortened  by  the  use  of  the  table 
in  Jour,  of  Chem.  Soc.,  Yol.  XVIII.  (1865)  p.  212. 

Very  fair  results  are  got  by  employing,  with  suitable  precau- 
tion, a  stream  of  carbon  dioxide  to  displace  the  air  of  the  combus- 
tion tube,  but  the  process  is  very  tedious,  the  sources  of  error  are 
more  numerous,  and  the  results  are  apt  to  be  higher  and  not  so 


644  ORGANIC   ANALYSIS.  [§  185. 

accordant  as  when  the  mercury  pump  is  used  to  evacuate  the 
tube. 

The  pump  above  described  has  been  in  use  for  eighteen  months 
without  any  repairs,  and  by  its  help  two  or  even  three  analyses 
may  be  performed  in  a  day. 

/3.  Determination  of  Nitrogen  l>y  conversion  into  Ammonia. 

VAKRENTRAPP  and  WILL'S  Method. 

§  185. 

This  method  may  be  applied  to  all  nitrogenous  compounds, 
except  those  containing  the  nitrogen  in  the  form  of  nitric  acid, 
hyponitric  acid,  &c.*  It  is  based  upon  the  same  principle  as  the 
method  of  examining  organic  bodies  for  nitrogen  (£  172,  1,  a\  viz., 
upon  the  circumstance  that,  when  nitrogenous  bodies  are  ignited 
with  an  alkali  hydroxide,  the  latter  is  decomposed,  yielding  water, 
the  oxygen  of  which  combines  with  carbon  to  CO,,  which 
remains  in  combination  with  the  alkali  as  carbonate,  whilst  the 
hydrogen  at  the  moment  of  its  liberation  combines  with  the  whole 
of  the  nitrogen  present  to  form  ammonia. 

In  the  case  of  substances  abounding  in  nitrogen,  such  as  uric 
acid,  mellon,  &c.,  the  whole  of  the  nitrogen  is  not  at  once  con- 
verted into  ammonia  in  this  process ;  a  portion  of  it  combining 
with  part  of  the  carbon  of  the  organic  matter  to  cyanogen,  which 
then  combines,  either  in  that  form  with  the  alkali  metal,  or  in  the 
form  of  cyanic  acid  with  the  alkali.  Direct  experiments  have 
proved,  however,  that  even  in  such  cases  the  whole  of  the  nitrogen 
is  ultimately  obtained  as  ammonia,  if  the  alkali  hydroxide  is  pres- 
ent in  excess,  and  the  heat  applied  sufficiently  intense. 

As  in  all  organic  nitrogenous  compounds  the  carbon  prepon- 
derates over  the  nitrogen,  the  oxidation  of  the  former,  at  the 
expense  of  the  water,  will  invariably  liberate  a  quantity  of  hydro- 
gen more  than  sufficient  to  convert  the  whole  of  the  nitrogen  pres- 
ent into  ammonia ;  for  instance, 

CIS"  +  2H20  =  CO,  +  ]STH3  +  H. 

[*  Vegetable  matters,  as  dried  plants,  containing  not  more  than  3  per  cent,  of 
NO5  may  be  analyzed  by  this  method.  In  a  case  where  6  per  cent,  of  N2O5was 
present,  a  loss  of  0'2  per  cent,  of  N  took  place  in  the  experiments  of  E. 
Schulze.—  Fres.  Zeitschrift  vi.  387.] 


§  185.]  OKGANIC   ANALYSIS.  645 

The  excess  of  the  liberated  hydrogen  escapes  either  in  the  free 
state,  or  in  combination  with  the  not  yet  oxidized  carbon,  accord- 
ing to  the  relative  proportions  of  the  two  elements  and  the  tem- 
perature, as  marsh  gas,  olefiant  gas,  or  vapor  of  readily  condensible 
hydrocarbons,  which  gases  serve  in  a  certain  measure  to  dilute  the 
ammonia.  As  a  certain  dilution  of  that  product  is  necessary  for 
the  success  of  the  operation,  I  will  here  at  once  state  that  sub- 
stances rich  in  nitrogen  should  be  mixed  with  more  or  less  of  some 
non-nitrogenous  body — sugar,  for  instance — so  that  there  may  be 
no  deficiency  of  diluent  gas. 

The  ammonia  is  determined  volumetrically,  see  §  196. 

aa.  Requisites. 

1.  The  objects  enumerated  §  174,  and  a  PORCELAIN  MORTAR  for 
mixing  the  weighed  substance. 

2.  A  COMBUSTION  TUBE  of  the  kind  described  §  174,  3 ;  length 
about  40  cm.,  wridth  about  12  mm.     The  combustion  is  effected  in 
an  ordinary  combustion  furnace. 

3.  SODA-LIME   (§  66,  5). — It  is  advisable  to  gently  heat  in  a 
platinum  or  porcelain  dish,  a  quantity  of  the  soda-lime  sufficient  to 
fill  the  combustion  tube,  so  as  to  have  it  perfectly  dry  for  the  pro- 
cess of  combustion.     In  the  analysis  of  non- volatile  substances,  the 
best  way  is  to  use  the  soda-lime  while  still  warm. 

4.  ASBESTOS. — A  small  portion  of  this  substance  is  ignited  in  a 
platinum  crucible  previous  to  use. 

5.  A  VERRENTRAPP  AND  WILL'S  BULB  APPARATUS. — This  may 
be  obtained  from  the  shops.     Fig.  97  shows  its  form.     It  is  filled 
to  the  extent  indicated  in  the  drawing  with  standard  sulphuric  or 


Fig.  97. 

hydrochloric  acid  §  192,  of  which  20  c.c.  should  be  employed.  The 
acid  is  introduced  either  by  dipping  the  point  into  the  acid,  and 
applying  suction  to  d,  or  by  means  of  a  burette. 


646  OKGANIC   ANALYSIS.  [§  185. 

In  order  to  guard  against  the  receding  of  the  acid  into  the 
combustion  tube,  ARENDT  and  KNOP  have  sug- 
gested the  form  indicated  fig.  98. 

6.  A  soft,  well-perforated  COKK,  which  fits  the 
combustion  tube  air-tight,  and  in  which  the  tube 
d  of  the  bulb  apparatus  fits  closely. 

7.  A  SUCTION-TUBE  of  caoutchouc  adapted  to 
the  point  of  the  bulb  apparatus. 

l)b.  The  Process. 

The  combustion  tube  is  half  filled  with  soda-lime,  which  is  then 
gradually  transferred  to  the  perfectly  dry,  and,  if  the  nature  of  the 
substance  permits,  rather  warm  mortar,  where  it  is  most  intimately 
mixed  with  the  weighed  substance,  forcible  pressure  being  care- 
fully avoided ;  a  layer  of  soda-lime,  occupying  about  3  cm.,  is  now 
introduced  into  the  posterior  part  of  the  combustion,  tube,  and  the 
mixture  filled  in  after  ;  the  latter,  which  will  occupy  about  20  cm., 
is  followed  by  a  layer  of  about  5  cm.  of  soda-lime,  which  has  been 
used  to  rinse  the  mortar,  and  this  again  by  a  layer  of  12  cm.  of 
pure  soda-lime,  leaving  thus  about  4  cm.  of  the  tube  clear.  The 
tube  is  then  closed  with  a  loose  plug  of  asbestos,  and  a  free  passage 
for  the  evolved  gases  formed  by  a  few  gentle  taps  ;  it  is  then  con- 
nected with  the  bulb  apparatus  by  means  of  the  perforated  cork, 
and  finally  placed  in  the  combustion  furnace  (see  fig.  97). 

To  ascertain  whether  the  apparatus  closes  air-tight,  some  air  is 
expelled  by  holding  a  piece  of  red  hot  charcoal  to  the  bulb  a,  and 
the  apparatus  observed,  to  see  whether  the  liquid  will,  upon  cooling, 
permanently  assume  a  higher  position  in  a  than  in  the  other  limb. 
The  tube  is  then  gradually  surrounded  with  ignited  charcoal,  com- 
mencing at  the  anterior  part,  and  progressing  slowly  towards  the 
tail,  the  operation  being  conducted  exactly  as  in  an  ordinary  com- 
bustion (§  175).  Care  must  be  taken  to  keep  the  anterior  part  of 
the  tube  tolerably  hot  throughout  the  process,  since  this  will 
almost  entirely  prevent  the  passage  of  liquid  hydrocarbons,  the 
presence  of  which  in  the  standard  acid  would  be  inconvenient. 
The  asbestos  should  be  kept  sufficiently  hot  to  guard  against  its 
retaining  water,  and  with  this,  ammonia.  The  combustion  should 
be  conducted  so  as  to  maintain  a  steady  and  uninterrupted  evolu- 
tion of  gas ;  there  is  no  fear  of  any  ammonia  escaping  unabsorbed, 
even  if  the  evolution  is  rather  brisk ;  but  the  operator  must  con- 
stantly be  on  his  guard  against  the  receding  of  the  acid,  which 


g  185.]  OKGANIC   ANALYSIS.  647 

takes  place  the  moment  the  evolution  of  gas  ceases,  and  this,  in 
some  instances,  with  such  impetuosity  as  to  force  the  acid  into  the 
combustion  tube,  which  of  course  spoils  the  whole  analysis.  This 
difficulty  may  be  readily  met,  however,  by  mixing  with  the  sub- 
stance an  equal  quantity  of  sugar,  which  will  give  rise  to  the  evo- 
lution of  more  permanent  gases  diluting  the  ammonia. 

When  the  tube  is  ignited  in  its  whole  length,  and  the  evolu- 
tion of  gas  has  totally  ceased,*  the  point  of  the  combustion  tube  is 
broken  off,  and  air  to  the  extent  of  several  times  the  volume  of  the 
gas  in  the  tube  is  sucked  through  the  apparatus,  to  force  all  the 
rest  of  the  ammonia  into  the  acid. 

Liquid  nitrogenous  compounds  are  weighed  in  small  sealed 
glass  bulbs,  and  the  process  is  conducted  as  directed  §  180,  with 
this  difference,  that  soda-lime  is  substituted  for  oxide  of  copper. 
It  is  advisable  to  employ  tubes  of  greater  length  for  the  combus- 
tion of  liquids  than  are  required  for  solid  bodies.  The  best  method 
of  conducting  the  operation,  is  to  heat  first  about  one-third  of  the 
tube  at  the  anterior  end,  and  then  to  force  the  liquid  from  the 
bulbs  into  the  tube  by  heating  the  hinder  end  of  the  latter ;  the 
expelled  liquid  will  thus  become  diffused  in  the  central  part  of  the 
tube,  without  being  decomposed.  By  a  progressive  application  of 
heat,  proceeding  slowly  from  the  anterior  to  the  posterior  end,  a 
steady  and  uniform  evolution  of  gas  may  be  easily  maintained. 

When  the  combustion  is  terminated,  the  bulb  apparatus  is 
emptied,  through  the  opening  at  the  point,  into  a  beaker,  and  rinsed 
with  water  until  the  rinsings  cease  to  manifest  acid  reaction. 

The  excess  of  acid  is  determined  by  means  of  standard  potash 
or  ammonia  solution  and  cochineal  tincture,  or,  if  the  acid  is  so 
colored  that  the  point  of  neutralization  cannot  readily  be  decided 
by  cochineal,  employ  slips  of  turmeric  paper  (see  §  196). 

It  is  advantageous  to  use  a  rather  dilute  acid,  1  c.  c.=  0*005  grin, 
of  nitrogen.  The  receiver  (fig.  99)  may  be  advantageously  substi- 
tuted for  the  bulb-tube.  The  tube  a — previously  provided  with 
the  caoutchouc  stopper  J — is  first  connected  by  the  aid  of  a  good 
cork  with  the  combustion  tube,  and  then  the  U-tube  c — having  been 
charged  with  the  proper  quantity  of  acid  from  a  MOHK'S  burette 
— is  added.  At  the  termination  of  the  combustion,  when  air  has 

*  This  is  indicated  by  the  white  color  which  the  mixture  reassumes  when  all 
the  carbon  deposited  on  the  surface  is  oxidized. 


648  OKGANIC   ANALYSIS.  [§  185. 

been  drawn  through  the  apparatus,  the  tube  a  is  rinsed  into  the 
apparatus  c,  some  tincture  of  cochineal  added,  and  standard  alkali 
run  into  the  tube  from  a  second  burette,  until 
the  acid  is  almost  neutralized.  ~Now  pour  the 
contents  of  the  apparatus  into  a  beaker,  rinse 
with  water,  and  complete  the  neutralization.  With 
this  receiver  neither  receding  nor  spirting  is 
possible.  By  not  pouring  out  the  fluid  till  the 
point  of  saturation  is  nearly  attained,  you  require 
less  water  for  rinsing  the  tube.  This  method-  is 
rapid  and  accurate. 

[From  the  results  of  a  critical  investigation  of 
Fi"™99  this  method  by  JOHNSON  and  JENKINS*  the  fol- 

lowing facts  may  be  here  added  : 

1.  The  efficiency  of  the  "  soda-lime"  mixture  described  §  66,  5, 
is  fully  confirmed.    It  is  easier  to  prepare  than  the  mixture  of  caus- 
tic lime  and  soda  (§  66,4)  formerly  used  for  this  purpose,  and  does 
not,  like  the  latter,  attract  moisture  readily  from  the  air,  and  is  not 
liable  to  swell  and  choke  the  tube  during  combustion. 

2.  Neither  the  highest  heat  possible  to  obtain  in  an  EKLEN- 
MEYEK  gas  combustion  furnace,  nor  a  long  layer  of  strongly  heated 
soda-lime,  nor  these  two  conditions  united,  occasion  any  appreciable 
dissociation  of  the  ammonia  formed  in  combustion. 

3.  A  suitable  length  of  the  anterior  layer  of  soda-lime  must  be 
secured  in  order  to  get  a  good  result.     With  O5  gram  of  sub- 
stances, such  as  are  encountered  in  agricultural  chemistry,  contain- 
ing less  than  8  per  cent,  of  nitrogen,  a  glass  tube  of  12  to  14  inches 
is  long  enough.     As  the  content  of  nitrogen  increases  to  10  per 
cent  or  over,  the  tubes  should  be  made  several  inches  longer.     In 
the  combustion  of  dried  blood  or  egg-albumin  a  tube  20 — 25  inches 
long  is  preferred,   and  the  mixture    of   soda-lime  and  substance 
should  occupy  rather  less  than  half  the  tube,  a  layer  of  pure  soda- 
lime  of  12  or  more  inches  long  being  essential  for  perfectly  destroy- 
ing the  volatile  organic  matters. 

4.  The*  long  anterior  layer  of  pure  soda-lime  must  be  brought 
to  SL  full  red  heat  before  heating  the  mixture,  and  must  be  so  kept 
throughout  the  combustion. 

5.  No  fumes  or  tarry  matters,  indicative  of  incomplete  combus- 
tion, should  appear  in  bulb-tube  or  receiver. 

*  Report  of  Connecticut  Agr.  Exp.  Station,  1878,  p.  111. 


§  186.]  ORGANIC   ANALYSIS.  649 

6.  When  the  combustion  proper  is  begun  under  the  conditions 
above  described,  it  can  be  carried  on  quite  rapidly  until  completed. 
The  contents  of  the  tubes  then  show  no  sign  of  unburned  carbon. 

7.  Equally  good  results  are  obtained  whether  the  mixture  is 
made  intimately  in  a  mortar,  or  more  roughly  by  stirring  with  a 
spatula  in  a  metallic  capsule  or  scoop,  or  by  mixing  in  the  tube 
with  a  wire.] 

Iron  gas  tubes  may  be  substituted  for  glass  tubes.  They  are 
closed  at  the  rear  with  a  cork,  carrying  a  bit  of  glass  tube  drawn 
out /to  a  sealed  tail.  The  mixture  is  confined  to  its  place  by  loose 
asbestos  plugs.  The  corks  are  kept  from  charring  by  wrapping  the 
end  of  the  tube  with  two  or  three  thicknesses  of  filter-paper,  which 
is  kept  wet  by  a  wash-flask,  or  by  dipping  the  depending  end  into 
a  vessel  of  water.  The  tubes  should  be  45  cm.  long,  and  5  cm.  at 
each  end  should  project  from  the  fire  and  be  protected  with  wet 
paper. 

C.  ANALYSIS  OF  ORGANIC  COMPOUNDS  CONTAINING  SULPHUR.* 

§186. 

The  usuai  method  of  determining  the  carbon  in  organic  bodies 
— viz.,  by  combustion  with  oxide  of  copper  or  lead  chromate — 
would  give  results  too  high  in  the  analysis  of  compounds  contain- 
ing sulphur,  since — more  especially  if  oxide  of  copper  is  used — a 
portion  of  the  sulphur  would  be  converted  in  the  process  into  sul- 
phurous acid,  which  would  be  absorbed  with  the  carbonic  acid  in 
the  potash  bulbs.  CARIUS  recommends  to  burn  substances  contain- 
ing sulphur  in  a  tube  60 — 80  cm.  long,  with  lead  chromate,  care 
being  taken  that  the  anterior  10 — 20  cm.,  which  contains  pure  lead 
chromate,  are  never  heated  above  low  redness.  The  lead  chromate 
may  be  used  again  three  or  four  times  without  refusion ;  and, 
finally,  if  treated  by  YOHL'S  method  (p.  124),  it  is  just  as  fit  for 
use  as  if  it  had  not  been  employed  for  the  combustion  of  a  sub- 
stance containing  sulphur. 

The  presence  of  sulphur  demands  no  modification  in  the  pro- 
cess described  §§  184  and  185  for  the  determination  of  nitrogen. 
In  substances  containing  oxygen  in  presence  of  sulphur,  the  oxygen 
is  estimated  from  the  loss. 

[*  WARREX'S  method  of  determining  carbon,  hydrogen,  and  sulphur  in  one 
operation  is  described  in  Am.  Journ.  Sci.,  vol.  41,  2d  ser.,  p.  40.] 


650  ORGANIC   ANALYSIS.  [§  186. 

As  regards  the  estimation  of  the  sulphur  in  organic  compounds, 
that  element  is  invariably  weighed  in  the  form  of  barium  sulphate, 
into  which  it  may  be  converted  either  in  the  dry  or  in  the  wet  way. 

a.  Methods  in  the  Dry  Way. 

1.  Method  suitable ,  more  particularly,  to  determine  the  sulphur 
in  non-volatile  Substances  poor  in  Sulphur,  e.g.,  in  the  so-called 
Protein  Compounds  (v.  LIEBIG). 

Put  some  lumps  of  potassa,  free  from  sulphuric  acid  (§  66,  7,  c) 
into  a  capacious  silver  dish,  add  -J  of  pure  potassium  nitrate,  and 
fuse  the  mixture,  with  addition  of  a  few  drops  of  water.  When 
the  mass  is  cold,  add  to  it  a  weighed  quantity  of  the  finely  pul- 
verized substance,  fuse  over  the  lamp,  stir  with  a  silver  spatula, 
and  increase  the  heat,  continuing  the  operation  until  the  color  of 
the  mass  shows  that  the  carbon  separated  at  first  has  been  com- 
pletely consumed.  Should  this  occupy  too  much  time,  you  may 
accelerate  it  by  the  addition  of  potassium  nitrate  in  small  portions. 
Let  the  mass  cool,  then  dissolve  in  water,  supersaturate  the  solu- 
tion with  hydrochloric  acid  in  a  capacious  beaker  covered  with  a 
glass  dish,  and  precipitate  with  barium  chloride.  Wash  the  pre- 
cipitate well  with  boiling  water,  first  by  decantation,  then  on  the 
filter.-  Dry  and  ignite.  Treat  the  ignited  barium  sulphate  as 
directed  p.  367;  if  this  latter  operation  is  omitted,  the  result 
is  almost  always  too  high. 

A  suitable  alcohol  lamp  is  preferable  to  a  gas  flame,  since  the 
latter  may  communicate  sulphur  to  the  fused  mass.  As  it  is  by 
no  means  easy  to  obtain  the  required  reagents  perfectly  free  from 
sulphur,  it  is  well  to  try  a  parallel  experiment,  using  the  same 
quantities  of  each  that  is  used  for  the  analysis,  and  if  an  appre- 
ciable amount  of  barium  sulphate  is  obtained,  make  the  necessary 
correction  in  the  analysis. 

2.  Method  adapted  'more  particularly  for  the  Analysis  of  non- 
volatile or  difficultly  volatile  Substances  containing  more  than  5 
per  cent,  of  Sulphur  (KOLBE  *). 

Introduce  into  the  posterior  part  of  a  straight  combustion  tube,f 
40 — 45  cm.  long,  a  layer,  7 — 8  cm.  long,  of  an  intimate  mixture  of 
8  parts  of  pure  anhydrous  sodium  carbonate,  and  1  part  of  pure 

*  Supplemente  zum  Handworterbuch,  205. 

f  Sealed  and  rounded  at  the  end  like  a  test  tube. 


§  186.]  ORGANIC   ANALYSIS.  651 

potassium  chlorate ;  after  tins  introduce  the  weighed  substance, 
then  another  layer,  7  or  8  cm.  long,  of  the  same  mixture ;  mix  the 
organic  compound  intimately  with  the  sodium  carbonate  and  potas- 
sium chlorate,  by  means  of  the  mixing  wire  (fig.  78,  p.  613) ;  fill 
up  the  still  vacant  part  of  the  tube  with  anhydrous  sodium  carbon- 
ate or  potassium  carbonate  mixed  with  a  little  potassium  chlorate. 
Clear  a  wide  passage  from  end  to  end  by  a  few  gentle  taps,  place 
the  tube  in  a  combustion  furnace,  heat  the  anterior  part  to  redness, 
and  then,  progressing  slowly  toward  the  posterior  part,  proceed  to 
surround  with  red-hot  charcoal  the  part  occupied  b}^  the  mixture. 
In  the  analysis  of  substances  abounding  in  carbon,  it  is  advisable 
to  introduce  into  the  posterior  part  of  the  tube  a  few  lumps  of 
pure  potassium  chlorate,  to  insure  complete  combustion  of  the  car- 
bon, and  perfect  conversion  into  sulphates  of  the  compounds  of 
potassa  with  the  lower  oxides  of  sulphur  that  may  have  formed. 
The  sulphuric  acid  in  the  contents  of  the  tube  is  determined  as  in  1. 

3.  Method  adapted  for  the  Analysis  both  of  non-volatile  and 
volatile  Substances,  but  more  especially  the  latter  (DEBUS  *). 

Dissolve  149  parts  of  potassium  dichromate  purified  by  recrys- 
tallization,  and  106  parts  anhydrous  sodium  carbonate  in  water, 
evaporate  the  solution  to  dryness,  reduce  the  lemon-colored  saline 
mass  to  powder,  heat  to  intense  redness  in  a  Hessian  crucible,  and 
transfer  still  hot  to  a  filling-tube  (fig.  77,  p.  613).+  "When  the 
powder  is  cold,  introduce  a  layer  of  it,  7 — 10  cm.  long,  into  a  com- 
mon combustion  tube  ;  then  introduce  the  substance,  and  after  this1 
another  layer,  7 — 10  cm.  long,  of  the  powder.  Mix  intimately 
by  means  of  the  mixing  wire,  then  fill  the  still  unoccupied  part  of 
the  tube  with  the  saline  mixture,  and  apply  heat  as  in  an  ordinary 
ultimate  analysis.  When  the  entire  mass  is  heated  to  redness, 
conduct  a  slow  stream  of  dry  oxygen  gas  over  it  for  \ — 1  hour. 
When  cold,  wipe  the  ash  off  the  tube,  cut  the  latter  into  several 
pieces  over  a  sheet  of  paper,  and  treat  them  in  a  beaker  with  a  suf- 
ficient quantity  of  water  to  dissolve  the  saline  mass.  Add  hydro- 
chloric acid  in  tolerable  excess,  then  some  alcohol,  and  apply  a 

*  Annal.  d.  Chem.  u.  Pharm.  76,  90. 

f  The  saline  mass  must  always  first  be  tested  for  sulphur.  For  this  purpose 
a  small  portion  of  it  is  reduced  with  hydrochloric  acid  and  alcohol,  barium 
chloride  added,  and  the  mixture  allowed  to  stand  12  hours  at  rest.  No  trace  of 
a  precipitate  should  be  discernible. 


652  ORGANIC   ANALYSIS.  [§  186. 

gentle  heat  until  the  solution  shows  a  beautiful  green  color ;  filter 
off  the  chromic  oxide  produced  by  the  combustion  (this  contains 
sulphuric  acid) ;  wash  first  with  water  containing  hydrochloric 
acid,  then  with  alcohol,  dry,  and  transfer  to  a  platinum  crucible ; 
add  the  filter-ash,  mix  with  1  part  of  potassium  chlorate  and  2 
parts  of  potassium  (or  sodium)  carbonate,  and  ignite  until  the 
chromic  oxide  is  completely  converted  into  alkalin  chromate.  Dis- 
solve the  fused  mass  in  dilute  hydrochloric  acid,  and  reduce  by 
heating  with  alcohol ;  add  the  solution  to  the  fluid  filtered  from 
the  chromic  oxide,  heat  the  mixture  to  boiling,  and  precipitate  the 
sulphuric  acid  with  barium  chloride.  DEBUS'S  test-analyses  were 
very  satisfactory ;  thus  he  obtained  99*76  and  99'50  of  sulphur  for 
100,  again  30'2  of  sulphur  in  xanthogenamide  for  30 '4,  &c. 

4.  Method  equally  adapted  for  the  Analysis  of  Solid  and 
Liquid  Volatile  Compounds.  (W.  J.  RUSSELL  ;  *  suggested  by 
BUNSEN.) 

Introduce  into  a  combustion  tube,  40  cm.  long,  sealed  at  the 
posterior  end,  first  2 — 3  grm.  pure  mercuric  oxide,  then  a  mixture 
of  equal  parts  of  mercuric  oxide  and  pure  anhydrous  sodium  car- 
bonate, mixed  with  the  substance,  and  fill  up  the  tube  with  sodium 
carbonate  mixed  with  a  little  mercuric  oxide.  Connect  the  open 
end  of  the  tube  with  a  gas  delivery  tube  dipping  under  water,  to 
effect  the  condensation  of  the  mercurial  fumes.  Place  a  screen  in 
front  of  the  part  of  the  tube  occupied  by  the  substance,  then  heat 
the  anterior  part  to  bright  redness,  and  maintain  this  temperature 
during  the  entire  process.  At  the  same  time,  heat  another  portion 
of  the  tube,  nearer  to  the  end,  but  not  to  the  same  degree  of  inten- 
sity, so  that  there  may  be  alternate  parts  in  the  tube  in  which  the 
mercuric  oxide  is  left  undecomposed.  When  the  part  before  the 
screen  is  at  bright  redness,  remove  the  screen,  heat  the  mixture 
containing  the  substance,  regulating  the  application  of  heat  so  as 
to  insure  complete  decomposition  in  the  course  of  10 — 15  minutes, 
and  heat  at  the  same  time  the  still  unheated  parts  of  the  tube,  and 
lastly  also  the  pure  oxide  of  mercury  at  the  extreme  end.  The 
gas  must  be  tested  from  time  to  time,  to  ascertain  whether  it  con- 
tains free  oxygen.  Dissolve  the  contents  of  the  tube  in  water, 
add  some  mercuric  chloride  to  decompose  the  sodium  sulphide 
which  may  have  formed,  acidify  with  hydrochloric  acid,  oxidize  the 

*  Quart.  Journ.  Chem.  Soc.  7,  212. 


§  186.]  ORGANIC   ANALYSIS.  653 

mercuric  sulphide  which  may  have  formed  with  potassium  chlo- 
rate, and  finally  precipitate  the  sulphuric  acid  with  oarium  chlo- 
ride. "W.  J.  RUSSELL  obtained  by  this  method  very  satisfactory 
results  in  the  analysis  of  pure  sulphur,  potassium  sulphocyanate, 
and  carbon  disulphide. 

b.  Method  in  the  Wet  Way.* 

According  to  RIVOT,  BEUDANT,  and  DAGUiN,t  the  sulphur  in 
organic  compounds  may  be  readily  determined  by  heating  with 
pure  solution  of  potassa,  adding  2  volumes  of  water  and  conducting 
chlorine  into  the  fluid.  When  the  oxidation  is  effected,  the  solu- 
tion is  acidified  and  freed  from  the  excess  of  chlorine  by  applica- 
tion of  heat,  then  filtered,  and  the  filtrate  precipitated  by  barium 
chloride.  Mr.  C.  J.  MEEZ,  in  my  laboratory,  has  employed  both 
this  method  and  v.  LIEBIG'S  (#,  1)  in  the  analysis  of  fine  horn 
shavings.  This  process  appears  convenient  and  exact.  \ 

Substances  leaving  an  ash  on  incineration,  and  which  may  there- 
fore be  presumed  to  contain  sulphates,  are  boiled  with  hydrochloric 
acid ;  the  solution  obtained  is  filtered,  and  the  filtrate  tested  with 
barium  chloride.  If  a  precipitate  of  barium  sulphate  forms,  the 
sulphur  contained  in  it  is  deducted  from  the  quantity  found  by 
one  of  the  methods  described  above ;  the  difference  gives  the  quan- 
tity of  the  sulphur  which  the  analyzed  substance  contains  in  organic 
combination. 

[<?.  Methods  depending  on  Combustion  in  a  Current  of 
Oxygen. 

"When  organic  compounds  containing  sulphur  are  burned  in  a 
current  of  oxygen  gas  in  a  combustion  tube,  usually  not  only  SO, 
or  sulphuric  acid,  but  SOa  also  is  formed.  Additional  means  of 
completing  the  oxidization  of  the  sulphur  and  absorbing  the  sul- 
phuric acid  are  required.  Several  methods  have  been  proposed  and 
used  for  attaining  the  desired  end.  C.  M.  WARREN  §  conducts  the 
products  of  combustion  over  heated  lead  dioxide,  thus  obtaining 

[*  For  the  excellent  processes  of  Carius,  see  Annal.  d.  Chem.  u.  Pharm.  116, 
11.] 

f  Comp.  rend.  1853,  835;  Journ.  f.  prakt.  Chem.  61,  135. 

\  Two  experiments  were  made  with  each  method,  on  horn  dried  at  100°.  The 
percentages  obtained  were  as  follows:  By  v.  Liebig's  method,  3*37  and  3 '345; 
by  the  present  method,  3 '31  and  3 '33. 

§  Zeitschr.  f.  anal.  Chem.  5,  169. 


654 


ORGANIC    ANALYSIS. 


[§  186, 


lead  sulphate  mixed  with  lead  dioxide.  BRUGLEMANN*  conducts 
the  products  of  combustion  over  quicklime  (or  soda-lime),  obtain- 
ing calcium  sulphate  mixed  with  quicklime.  MiXTEuf  uses  bro- 
mine and  water  to  complete  the  oxidization  and  absorb  the  sulphu- 
ric acid.  SAUERIJ:  uses  also  bromine  (a  hydrochloric  solution)  for 
the  same  purpose. 

These  methods  are  applicable  to  all  classes  of  organic  com- 
pounds containing  sulphur.     The  two  last  mentioned  possess  the 


Fig.  100. 

advantage  that  the  sulphur  is  obtained  as  free  sulphuric  acid  in  a 
solution  containing  no  fixed  matter,  and  consequently  in  a  con- 
dition to  be  easily  and  accurately  determined. 

*  Zeitschr.  f.  anal.  Chem.  15, 1,  and  15,  175. 

f  American  Jour.  Sci.  and  Arts,  iv.  90. 

j  Zeitschr.  f.  anal.  Chem.  12,  32,  and  12,  178. 


§  186.]  ORGANIC   ANALYSIS.  655 

1.  MIXTER'S  method  is  described  *  as  follows : 

The  apparatus  (fig.  100)  is  designed  to  effect  the  combustion  in 
a  confined  volume  of  gas ;  a  device  resorted  to  on  account  of  the 
difficulty  of  completely  condensing  by  liquid  absorbents  in  U-tubes 
the  dense  white  fumes  of  sulphuric  acid  produced  by  combustion. 
The  bottle  (a)  has  a  capacity  of  from  4  to  10  litres,  according  to 
the  amount  of  oxygen  required.  The  neck  should  be  large  enough 
for  a  stopper  35  to  40  mm.  in  diameter.  The  condenser  J  is  made 
of  rather  thin  tubing  14  mm.  in  diameter ;  at  the  upper  end  it  is 
expanded  to  a  bulb  in  order  to  admit  some  motion  to  the  tube  c  d. 
Below  the  bulb  it  is  surrounded  by  a  water-jacket  22  cm.  high : 
from  the  point  where  it  enters  the  stopper  of  the  bottle  it  is  nar- 
rowed somewhat  for  convenience  of  fitting.  The  combustion  tube 
c  d  is  made  of  hard  glass  of  12 — 15  mm.  internal  diameter ;  the 
portion  c  is  18  cm.  from  curve  to  curve,  and  is  protected  by  a 
sheet-iron  trough  lined  with  asbestos ;  the  part  d  is  from  35  to  45 
cm.  in  length.  The  wire  attached  at  I  is  to  sustain  c  in  case  d 
breaks ;  c  is  joined  to  b  by  a  collar  of  black  rubber.  The  U-tube  e 
is  connected  with  d  by  a  rubber  collar  drawn  over  the  latter  at  ~k ; 
this  U-tube  is  slightly  inclined,  that  no  liquid  may  run  against  the 
rubber  connectors.  The  tube  f  connects  a  with  e\  it  is  narrowed 
at  both  ends  to  10  mm.  diameter.  Near  the  upper  end  it  is  jointed 
by  a  piece  of  black-rubber  tubing  in  order  that  the  apparatus  may 
be  easily  disconnected  at  ~k.  The  ends  of  f  extend  2  cm.  or  more 
beyond  the  stoppers.  Through  the  rubber  stopper  i  a  small  glass 
tube  passes  beyond  the  end  of  /,  where  it  is  narrowed  to  an  open- 
ing of  1  mm.  The  double  bulb  tube/  is  to  accommodate  varia- 
tions of  pressure,  and  to  admit  air  as  the  original  volume  of  gas 
diminishes  during  the  combustion.  The  tubes  J,  c,  d,  and/  should 
at  no  point  have  an  internal  diameter  less  than  8  mm. — 10  mm.  is 
preferable — and  the  narrowed  ends  should  be  cut  obliquely  that 
drops  of  water  may  not  obstruct  the  circulation.  The  rubber  stop 
pers  and  connections  should  be  freed  from'  adhering  sulphur  by 
heating  in  a  solution  of  soda.  The  joints  of  the  apparatus  are  suf- 
ficiently tight  when  water  will  stand  in  one  limb  of  the  safety  tube. 

The  bottle  a  is  filled  over  water  with  oxygen,  and,  if  necessary, 
rinsed  with  distilled  water ;  a  few  drops  of  bromine  are  poured  in, 
the  tubes  adjusted,  and  a  slow  stream  of  water  made  to  flow  through 

*  American  Jour.  Sci.  and  Arts,  iv.  90. 


656  ORGANIC   ANALYSIS.  [§  186. 

the  water-jacket.  The  assay,  if  not  volatile,  is  introduced  into  the 
tube  d  in  a  platinum  tray,*  which  should  not  fill  more  than  half 
the  bore  of  d,  leaving  space  enough  for  the  free  circulation  of  the 
oxygen.  The  part  c  is  gradually  heated  and  kept  hot  during  the 
combustion.  This  hot  inclined  tube  acts  as  a  chimney ;  the  heated 
gases  rise  in  it,  pass  into  the  cold  tube  b  and  fall,  thus  causing  a 
constant  stream  of  gas  to  pass  over  the  assay.  It  is  important  to 
ignite  the  assay  without  distilling  off  any  considerable  portion. 
To  do  this  a  small  splinter  of  wood  may  be  placed  in  contact  with 
that  part  of  the  substance  nearest  Z,  or  that  end  of  the  tray  may 
hold  a  thin  layer  of  the  assay,  which  is  heated  as  rapidly  as  safety 
allows  by  a  lamp  held  in  the  hand.  To  insure  a  full  supply  of  gas 
in  the  tube  d  at  the  commencement  of  the  combustion,  oxygen  is 
passed  from  a  gasometer  through  the  tube  i  till  the  white  fume 
which  appears  in  the  condenser  b  passes  into  a.  The  products  of 
combustion  being  denser  fall  to  the  bottom  of  the  bottle,  and  for  a 
while  displace  the  oxygen,  thus  increasing  the  circulation.  After 
the  substance  is  ignited,  the  fire  passes  to  the  other  end  of  the  tray. 
The  part  of  the  tube  about  the  tray  is  heated  by  a  lamp  as  is  re- 
quired to  keep  up  the  combustion.  At  the  end  of  the  operation 
the  heat  is  increased.  If  drops  of  liquid  collect  in  c,  and  are  liable 
to  run  down  to  the  hotter  parts  of  the  tube,  they  should  be  driven 
off  by  heat.  If  carbonic  acid  be  the  principal  product  of  the  com- 
bustion, there  is  little  change  in  the  volume  of  gases  in  the  appa- 
ratus ;  but  if  water  and  sulphuric  acid  are  formed  in  much  quantity, 
the  volume  is  diminished  and  air  enters  through  the  safety 
tube. 

Most  solid  substances  heated  alone  in  the  open  tray  yield  vola- 
tile products  too  rapidly  for  entire  combustion,  but  if  mixed  with 
sand  in  suitable  proportion  they  burn  slowly  and  completely. 
Liquids  should  be  enclosed  .in  narrow  tubes  sealed  at  one  end  and 
drawn  out  at  the  other  to  a  capillary  bore  for  two  or  three  inches 
of  length.  Upon  the  point  of  the  tube  a  bit  of  platinum  sponge 
is  fixed  to  assist  the  oxidation.  The  liquid  should  not  fill  more 
than  two  thirds  of  the  wider  part  of  the  tube. 

Before  introducing  very  volatile  substances,  the  10  cm.  of  the 

*  A  platinum  tray  which  answers  well  may  be  made  10  to  20  cm.  long,  10  mm. 
wide,  and  7  to  10  mm.  deep  by  bending  thin  foil  over  a  glass  tube.  The  ends 
may  be  roughly  bent  together  or  left  open. 


§  186.]  ORGANIC   ANALYSIS.  657 

combustion  tube  I  d  should  be  heated  to  dull  redness.  Oxygen  is 
passed  in  at  t,  the  tubes  are  disjointed  at  &,  and  the  tube  holding 
the  assay  is  then  pushed  in,  till  the  platinum  just  reaches  the  heated 
zone.  The  apparatus  being  connected  at  &,  slow  volatilization  of 
the  liquid  is  effected  by  cautiously  applying  a  flame  under  the 
empty  portion  of  the  tube  containing  the  substance,  so  as  to  main- 
tain the  platinum  sponge  in  a  steady  glow.  As  soon  as  a  cloud  of 
combustion-products  appears  in  the  -vessel  a,  oxygen  is  shut  off 
from  i.  When  all  the  liquid  has  distilled  from  the  interior  tube, 
the  tube  c  d  is  cooled  slowly  and  the  apparatus  is  left  for  two 
hours  or  until  the  fume  has  entirely  subsided.  If  no  odor  of  bro- 
mine be  perceptible  when  the  apparatus  is  disconnected  at  ~k  to 
remove  the  tray  or  tube,  a  few  drops  of-  it  should  be  poured  through 
a  funnel-tube  put  in  the  place  of  j,  and  the  whole  allowed  to 
stand  some  time  to  insure  complete  oxidation  of  the  sulphur-com- 
pounds and  deposition  of  the  sulphuric  acid. 

The  tubes  d  and  e  are  then  rinsed  into  a  beaker,  this  water  is 
poured  into  J,  which  is  then  thoroughly  washed  by  the  aid  of 
the  wash-bottle ;  the  large  rubber  stopper  is  lifted  from  the  bottle 
and  the  lower  part  of  b  rinsed ;  without  removing  the  tube/*  from 
the  stopper,  it  is  rinsed  into  a  beaker,  and  finally  the  bottle  is  care- 
fully washed.  The  solution  obtained,  which  need  not  exceed  500 
c.  c.,  is  evaporated  to  a  small  volume,  filtered  if  necessary,  and  the 
sulphuric  acid  is  determined  by  precipitation  with  barium  chloride, 
observing  all  precautions  mentioned  in  §  132,  1.  In  case  the  sub- 
stance leaves  an  ash  or  residue  in  the  tray,  this  must  be  dissolved 
in  aqua  regia,  the  nitric  acid  removed  by  evaporation  with  strong 
chlorhydric  acid,  and  any  sulphuric  acid  it  may  contain  separated  in 
the  usual  manner.  In  the  use  of  this  apparatus  there  is  no  danger 
from  explosions  if  care  be  taken  to  have  the  combustion  tube  hot 
enough  to  ignite  combustible  vapor.  Before  attempting  to  burn  a 
substance  in  the  apparatus,  it  is  best  to  try  it  in  a  large  inclined 
tube  open  at  both  ends,  or  with  oxygen  supplied  at  the  lower  end. 
Such  a  preliminary  trial  will  usually  indicate  the  precautions  neces- 
sary in  burning  the  substance  in  the  apparatus. 

For  the  determination  of  sulphur  in  substances  rich  in  sulphur, 
•5  to  '75  grm.,  requiring  about  4  litres  of  oxygen,  may  be  used. 
When  but  little  sulphur  is  present,  a  combustion  of  2*  gnns.  may 
be  effected  with  9  litres  of  oxygen.  External  heat  is  best  applied 


658 


OKGANIC   ANALYSIS. 


[§  186. 


to  the  part  of  the  tube  containing  the  substance  by  a  Bunsen  burner 
held  in  the  hand.  The  length  of  time  required  for  the  actual  com- 
bustion seldom  exceeds  20  minutes. 

This  method  gives  very  accurate  results. 

2.  SAUER'S  Method,  modified  ~by  MIXTEK.* 

a.  If  the  substance  gives  off  but  little  volatile  matter  on  heat- 
ing, e.g.,  coke,  anthracite  coal,  <&c. 

A  combustion  tube  30  to  40  cm.  in  length  is  drawn  out  quite 
narrow  at  one  end,  and  the  drawn  out  narrow  part  is  bent  down- 
ward at  a  right  angle  and  fitted  by  means  of  a  perforated  stopper 
into  the  tl-tube  A,  fig.  101,  containing  aqueous  solution  of  bro- 


Fig.  101. 


Fig.  102. 

mine  and  also  a  large  drop  of  undissolved  bromine.  The  globule 
of  bromine  is  made  to  rest  at  the  point  f  by  giving  the  apparatus 
a  suitable  inclination.  The  combustion  tube  is  laid  in  a  combus- 
tion furnace,  and  the  substance  contained  in  a  tray  is  pushed  into 

*Am.  Journ.  Chem.,  2,  396. 


§  186.]  ORGANIC   ANALYSIS.  659 

the  open  end  about  15  cm.  This  end  is  then  closed  with  a  stop- 
per, through  which  passes  a  glass  tube.  Pure  oxygen  gas  is  then 
conducted  into  the  combustion  tube,  and  the  part  containing  the 
trav  is  heated  to  redness.  If  during  the  process  the  bromine  in 
solution  becomes  nearly  exhausted  by  the  action  of  sulphurous 
acid,  a  portion  of  the  undissolved  globule  is  shaken  over  into  the 
narrow  part  e  of  the  U-tube,  where  it  is  rapidly  dissolved  by  the 
agitation  caused  by  the  passing  gas-bubbles.  In  order  to  complete 
the  condensation  of  fumes  of  sulphuric  acid  which  may  pass 
through  the  U-tube,  they  are  conducted  by  means  of  the  tube  g 
to  the  bottom  of  the  bottle  B,  which  has  a  capacity  of  about  •  8 
litres.  The  bottom  of  the  bottle  should  be  barely  covered  with 
water.  During  the  process  of  combustion  a  cloud  of  fumes  inav 
be  observed  in  the  lower  part  of  the  bottle,  while  the  air  in  the 
upper  part  remains  perfectly  clear.  After  combustion  is  com- 
pleted, the  tube  g  is  removed,  and  the  bottle  with  its  mouth  closed 
is  allowed  to  stand  until  the  visible  fumes  are  absorbed.  The  com- 
bustion tube  is  rinsed  to  remove  sulphuric  acid  w^hich  may  have 
condensed  in  the  part  near  the  U-tube.  The  rinsings  are  added  to 
the  united  solutions  obtained  in  A  and  B.  The  solution  contain- 
ing the  sulphuric  acid  is  now  heated  to  remove  free  bromine,  and 
concentrated  if  the  volume  appears  too  great.  The  sulphuric  acid 
in  it  is  determined  as  in  the  similar  solution  obtained  by  the  pro- 
cess described  above  in  1. 

If  the  operator  cannot  procure  a  U-tube  of  the  form  represented 
by  A,  the  more  common  form  shown  by  fig.  99  may  be  used.  In  that 
case  it  is  best  to  use  a  saturated  solution  of  bromine  in  hydrochloric 
acid,  of  which  the  U-tube  should  contain  12  to  15  c.  c.  when  filled 
to  extent  indicated  in  fig.  99.  On  account  of  the  small  volume  of 
liquid  which  can  be  used  in  such  tube,  an  aqueous  solution  would 
hardly  suffice.  The  free  hydrochloric  acid  should  be  nearly  all 
removed  by  evaporation  from  the  final  solution  of  sulphuric  acid 
before  proceeding  to  precipitate  the  latter  with  barium  chloride. 

If  inorganic  matter  remains  in  the  tray  af tei  completing  the  com- 
bustion, it  is  to  be  treated  as  directed  in  c,  1. 

P.  The  substance  gives  off  volatile  matter  at  a  high  temperature. 

A  combustion  tube  about  85  cm.  long,  narrowed  at  the  point 
indicated  by  c  in  fig.  102,  is  employed.  Having  introduced  the 
substance  in  a  tray  (or  if  volatile  at  the  ordinary  temperature  in 


660  ORGANIC   ANALYSIS.  [§  187. 

bulb  tube  with  capillary  orifice),  the  narrow  part  of  the  combus- 
tion tube  and  also  a  portion  beyond  extending  to  within  10  or  15 
cm.  of  the  end  entering  the  U-tube  is  heated  to  dull  redness  in  a 
combustion  furnace.  Oxygen  gas  is  now  conducted  by  means  of 
the  hard  glass  tube  a  to  the  point  c  beyond  the  tray.  At  the  same 
time  a  very  slow  current  of  carbon  dioxide  is  made  to  enter  through 
the  tube  b  in  order  to  prevent  vapors  from  receding.  Now,  by  a 
cautious  application  of  heat  the  volatile  matter  in  the  tray  is  first 
distilled  off  and  burned  by  the  constantly  supplied  current  of  oxy- 
gen. Next  the  combustion  of  any  fixed  residue  remaining  in  the 
tray  is  effected  by  transferring  the  supply  of  oxygen  from  a  to  J, 
and  that  of  carbon  dioxide  from  J  to  a.  The  only  use  of  carbon 
dioxide  at  this  stage  is  to  prevent  products  of  combustion  from 
entering  the  tube  a.  The  combustion  tube  during  the  process  is 
connected  with  the  same  absorbing  apparatus  as  used  in  2,  a.  The 
remaining  part  of  the  process  is  also  indicated  as  in  2,  a. 

MIXTER*  obtained  quite  satisfactory  results  with  this  process. 
When  very  volatile  substances,  e.g.,  carbon  disulphide,  are  to  be 
burned,  it  is  necessary  to  apply  heat  very  cautiously  to  the  part  of 
the  tube  containing  the  substance,  so  that  the  flame  produced  by 
the  meeting  of  the  combustible  vapor  with  oxygen  shall  be  a  few 
millimetres  ~back  of  the  end  of  the  tube  delivering  the  oxygen.] 

D.  DETERMINATION  OF  PHOSPHORUS  IN  ORGANIC  COMPOUNDS. 

§  187. 

The  phosphorus  in  organic  compounds  is  determined  by  methods 
similar  to  those  employed  for  determination  of  sulphur  in  organic 
compounds,  i.e.,  the  organic  substance  is  oxidized  either  in  the  wet 
or  dry  way,  and  a  solution  is  obtained  in  which  the  phosphoric  acid 
formed  by  oxidization  is  determined. 

For  oxidation  the  methods  given  in  §  186,  1,  2,  4,  are  suit- 
able. 

From  the  solution  obtained  phosphoric  acid  is  precipitated, 
either  directly  with  ammonium  chloride,  magnesium  chloride,  and 
ammonia  mixture,  or  with  molybdic  acid  solution,  after  removing 
hydrochloric  acid  by  repeated  evaporation  with  nitric  acid. 

The  phosphorus  cannot  be  determined  by  incineration  of  the 

*Am.  Journ.  Chem.,  2,  396. 


§  188.]  ORGANIC   ANALYSIS.  661 

substance  and  examination  of  the  ash.  Yitellin,  which  when 
treated  with  nitric  acid  gives  3  per  cent,  of  phosphoric  acid,  yields 
barely  0*3  per  cent,  of  ash  (Y.  BAUMHAUER). 

If  a  substance  contains  phosphorus  both  in  an  unoxidized  state 
and  in  the  form  of  phosphates,  treat  a  separate  portion  with  hydro- 
chloric acid,  filter  if  necessary  and  determine  the  phosphoric  acid 
in  the  solution.  The  quantity  thus  found  is  deducted  from  the 
total  phosphoric  acid  found  in  the  portion  submitted  to  oxidation 
in  order  to  find  the  amount  which  existed  in  the  compound  in  an 
unoxidized  state. 


E.  ANALYSIS  OF  ORGANIC  SUBSTANCES  CONTAINING  CHLORINE, 
BROMINE,  OR  IODINE. 

§  188. 

Substances  containing  Bromine  and  Iodine  are  analyzed  gene- 
rally in  the  same  manner  as  those  containing  Chlorine. 

Those  portions  of  the  following  §  which  are  enclosed  between 
square  brackets  refer  exclusively  to  combinations  of  Iodine  or  Bro- 
•iiiine*  as  the  case  may  be. 

The  combustion  of  organic  substances  containing  chlorine  with 
oxide  of  copper  gives  rise  to  the  formation  of  cuprous  chloride, 
which,  were  the  process  conducted  in  the  usual  manner,  would 
condense  in  the  calcium  chloride  tube,  and  would  thus  vitiate 
the  determination  of  the  hydrogen.  This  and  every  other  error 
may  be  prevented  by  the  employment  of  lead  chromate  (§  177). 
The  chlorine  is,  in  that  case,  converted  into  lead  chloride,  and 
retained  in  that  form  in  the  combustion  tube. 

If  the  combustion  is  effected  with  oxide  of  copper  in  a  current 
of  oxygen,  the  cuprous  chloride-is  decomposed  by  the  oxygen,  oxide 
of  copper  and  free  chlorine  being  formed  ;  the  latter  is  retained 
partly  in  the  calcium  chloride  tube,  partly  in  the  potash  bulbs.  To 
remedy  this  defect,  STAEDELER*  proposes  to  fill  the  anterior  part 
of  the  tube  with  clean  copper  turnings ;  these  must  be  kept  red-hot 
during  the  combustion,  and  the  current  of  oxygen  must  be  arrested 
the  moment  they  begin  to  oxidize.  K.  KRAUT)*  observes  with  ref- 
erence to  this  process  that  it  is  well  to  place  a  roll  of  silver  foil, 

*  Annal.  d.  Chem.  u.  Pharm.  69,  335.        f  Zeitschr.  f.  anal.  Chem.  2,  242. 


662  OBGANIC   ANALYSIS.  [§  188. 

about  5  inches  long,  in  front  of  the  layer  of  metallic  copper.  In 
the  absence  of  the  silver  the  transmission  of  oxygen  has  to  be  con- 
ducted with  caution,  in  order  that  no  chlorine  may  be  expelled 
from  the  cuprous  chloride  first  formed,  but  by  adopting  KRAUT'S 
recommendation  we  may  continue  passing  the  gas  without  fear  till 
it  escapes  free  from  the  potash  tube.  [In  the  case  of  substances 
containing  iodine,  it  is  needless  to  employ  metallic  copper  as  well 
as  silver  foil.]  The  silver  may  be  used  over  and  over  again,  but 
at  last  requires  ignition  in  a  stream  of  hydrogen.  According  to 
A.  YOLCKEK,*  the  evolution  of  chlorine  may  be  prevented  by  mix- 
ing the  oxide  of  copper  with  ^  lead  oxide. 

[In  the  analysis  of  bodies  containing  bromine  the  above  methods 
do  not  always  answer,  v.  GoRtip-BESANEzf  satisfied  himself  of  this 
by  analyzing  dibromotyrosin.  Whether  this  body  was  burnt  with 
lead  chromate,  with  a  mixture  of  lead  chromate  and  potassium  chro- 
mate, with  oxide  of  copper  and  oxygen  and  an  anterior  layer  of 
lead  chromate,  with  an  anterior  layer  of  copper  turnings,  whether 
mixed  or  in  the  platinum  boat,  in  whichever  way  the  analysis  was 
performed  the  carbonic  acid  always  came  out  several  per-cents.  too 
low,  because  metallic  bromide  was  formed,  which  fused  and 
enclosed  carbon,  thereby  preventing  its  oxidization.  The  following 
process,  on  the  contrary,  yielded  good  results :  Into  a  combustion 
tube  drawn  out  to  a  long  point,  introduce  first  a  three-inch  layer  of 
oxide  of  copper,  then  a  plug  of  asbestos,  then  a  mixture  of  the  sub- 
stance (finely  powdered)  with  about  an  equal  weight  of  well-dried 
lead  oxide  in  a  porcelain  boat ;  again  a  plug  of  asbestos,  then  gran- 
ulated oxide  of  copper,  then  lead  chromate  or  copper  turnings. 
First  heat  the  anterior  and  then  the  posterior  layers  to  ignition, 
and  warm  the  part  where  the  boat  is  very  cautiously  and  gradu- 
ally ;  everything  combustible  distils  over,  arrives  at  the  oxide  of 
copper  in  the  form  of  vapor,  and  is  there  burnt.  In  the  boat  noth- 
ing remains  but  a  mixture  of  lead  bromide  and  oxide.  Complete 
the  combustion  with  oxygen,  taking  care  not  to  heat  the  point 
where  the  boat  is  too  strongly,  nor  continue  the  transmission  of 
oxygen  longer  than  necessary.  Observe  also  that  no  copper  bromide 
sublimes  into  the  calcium  chloride  tube.] 

As  regards  the  determination  of  the  chlorine  itself,  this  is  usu- 
ally effected  either  (a)  by  igniting  the  substance  with  alkalies  or 


*  Chem.  Gaz.  1849,  245,  29.  \  Zeitschr.  f.  anal.  Chem.  1,  439. 


§  188.]  ORGANIC    ANALYSIS.  663 

alkali-earths,  by  which  process  all  the  chlorine  is  obtained  as  chlo- 
ride, or  (1j)  by  oxidizing  the  substance  with  nitric  acid,  &c.,  in  a 
sealed  tube. 

a.  As  chlorine-free  lime  is  easily  obtainable  (by  burning  mar- 
ble ),  this  body  is  usually  preferred  to  effect  the  decomposition.  It 
must  always  be  tested  for  chlorine  previous  to  use. 

Introduce  into  a  combustion  tube,  about  40  cm.  long,  the  pos- 
terior end  of  which  is  sealed  and  rounded  like  a  test  tube,  a  layer 
of  lime,  6  cm.  long,  then  the  substance,  after  this  another  layer  of 
lime,  6  cm.  long,  and  mix  with  the  wire ;  fill  the  tube  almost  to  the 
mouth  with  lime,  clear  a  free  passage  for  the  evolved  gases  by  a 
few  gentle  taps,  and  apply  heat  in  the  usual  way.  Volatile  fluids 
are  introduced  into  the  tube  in  small  glass  bulbs.  When  the  decom- 
position is  terminated,  dissolve  in  dilute  nitric  acid,  and  precipitate 
with  solution  of  silver  nitrate  (§  141).  KOLBE  recommends  the  fol- 
lowing process  to  obtain  the  contents  of  the  combustion  tube  : —  t 
When  the  decomposition  is  completed,  remove  the  charcoal,  insert 
a  cork  into  the  open  end  of  the  tube,  remove  every  particle 
of  ash,  and  immerse  the  tube,  still  hot,  with  the  sealed  end 
downwards,  into  a  beaker  filled  two-thirds  with  distilled  water; 
the  tube  breaks  into  many  pieces,  and  the  contents  are  then  more 
readily  acted  upon.  As  in  this  method  the  ignition  of  compounds 
abounding  in  nitrogen  may  be  attended  with  formation  of  calcium 
cyanide  or  sodium  cyanide,*  the  separation  of  the  silver  chloride 
and  the  cyanide,  if  required,  is  to  be  effected  by  the  process  given 
in  §  169,  6,  b  (NETJBAUER  and  KERXERf).  [In  determining  iodine 
by  this  method,  a  little  iodine  set  free  by  action  of  nitric  acid  must 
be  converted  in  hyriodic  acid  by  addition  of  a  little  sulphurous 
acid  before  precipitating  with  silver  nitrate.]  In  the  analysis  of 
acid  organic  compounds  containing  chlorine  (e.g.,  chlorospiroylic 
acid),  the  chlorine  may  often  be  determined  in  a  simpler  manner, 
viz.,  by  dissolving  the  substance  under  examination  in  an  excess  of 
dilute  solution  of  potassa,  evaporating  to  dryness,  and  igniting  the 
residue,  by  which  means  the  whole  of  the  chlorine  present  is  con- 
verted into  a  soluble  chloride  (Lowio). 


*  The  formation  of  cyanides  may  be  prevented  by  using,  instead  of  lime,  a 
mixture  of  lime  and  soda,  obtained  by  slaking  3  parts  quicklime  in  a  solution  of 
1  part  sodium  hydroxide  (free  from  chlorine)  and  heating  the  mixture  to  dryness 
in  a  silver  dish.  Rose  Handb.  der  Anal.  Chem.,  Ed.  6  by  Finkener,  ii.  735. 

f  Annal.  d.  Chem.  u.  Pharm.  101,  324,  344. 


664  ORGANIC   ANALYSIS.  [§  189. 

Z>.  In  more  readily  decomposable  compounds,  e.g.,  in  the  sub- 
stitution products  of  acids,  the  halogen  may  also  be  determined  by 
decomposing  the  substance  by  contact  during  several  hours  with 
water  and  sodium  amalgam,  acidifying  the  fluid  with  nitric  acid, 
and  precipitating  with  silver  solution  ( 


F.  ANALYSIS  OF  ORGANIC  COMPOUNDS  CONTAINING  INORGANIC 

BODIES. 

.   §189. 

In  the  analysis  of  organic  compounds  containing  inorganic 
bodies,  it  is,  of  course,  necessary  first  to  ascertain  the  quantity  of 
the  latter  before  proceeding  to  the  determination  of  the  carbon, 
&c.,  as  otherwise  the  amount  of  the  organic  -body  whose  constitu- 
ents have  furnished  the  carbonic  acid,  water,  &c.,  not  being  known, 
it  would  be  impossible  to  estimate  the  oxygen  from  the  loss. 

If  the  substances  in  question  are  salts  or  similar  compounds, 
their  basic  radicals  are  determined  by  the  methods  given  in  the 
Fourth  Section  ;  but  in  cases  where  the  inorganic  bodies  are  of  a 
nature  to  be  regarded  more  or  less  as  impurities  (e.g.,  the  ash  in 
coal),  they  may  usually  be  determined  with  sufficient  accuracy 
by  the  combustion  of  a  weighed  portion  of  the  substance,  in  an 
obliquely  placed  platinum  crucible,  or  in  a  platinum  dish.  In  the 
analysis  of  substances  containing  fusible  salts,  even  long-continued 
ignition  will  often  fail  to  effect  complete  combustion,  as  the  carbon 
is  protected  by  the  fused  salt  from  the  action  of  the  oxygen.  In 
such  cases,  the  best  way  to  effect  the  purpose  is  to  carbonize  the 
substance,  treat  the  mass  with  water,  and  incinerate  the  undissolved 
residue  ;  the  aqueous  solution  is,  of  course,  likewise  evaporated  to 
dryness,  and  the  weight  of  the  residue  added  to  that  of  the  ash. 

If  organic  compounds  whose  ash  contains  potassium,  sodium, 
barium,  strontium,  or  calcium  are  burnt  with  oxide  of  copper,  part 
of  the  carbonic  acid  evolved  remains  as  carbonate  of  these  metals. 
As,  in  many  cases,  the  amount  of  carbonic  acid  thus  retained  is  not 
constant,  and  the  results  are,  moreover,  more  accurate  if  the  whole 
amount  of  the  carbon  is  expelled  and  weighed  as  carbonic  acid,  the 
combustion  is  effected  with  lead  chromate,  with  addition  of  -J-  of 
potassium  dichromate,  according  to  the  directions  given  in  §  177. 

*  Jahresb.  v.  Kopp.  u.  Will.  1861,  832. 


§  189  ]  ORGANIC   ANALYSIS.  665 

Accurate  experiments  have  shown  that  in  this  case  not  a  trace  of 
carbonic  acid  remains  with  the  bases. 

If  the  substance  is  weighed  in  a  porcelain  or  platinum  boat,  and 
the  combustion  is  effected  according  to  §  178,  the  ash,  carbon,  and 
hydrogen  may  be  determined  in  one  portion.  The  amount  of  car- 
bonic acid  contained  in  the  ash  is  added  to  that  found  by  the  pro- 
cess of  combustion ;  if  the  carbonic  acid  in  the  ash  cannot  be  cal- 
culated, as  in  the  case  of  alkali  carbonates,  it  may  be  determined  by 
means  of  fused  borax  (§  139,  II.,  c). 

In  burning  substances  containing  mercury,  the  arrival  of  any  of 
the  metal  at  the  calcium  chloride  tube  may  be  prevented  by  having 
a  layer  of  copper-turnings  in  the  anterior  part  of  the  combustion 
tube,  and  by  not  allowing  the  foremost  portion  to  get  too  hot. 


II. 


SPECIAL   PART. 


1.    ANALYSIS    OF  FKESH  WATER  (SPRING-WATER 
RIVER-WATER,  &0.).* 

§190. 

THE  analysis  of  the  several  kinds  of  fresh  water  is  usually 
restricted  to  the  quantitative  estimation  of  the  foDowing  sub- 
stances : 

a.  Basic  metals :  Sodium,  calcium,  magnesium. 

b.  Acids:    Sulphuric  acid,  nitric   acid,  silicic   acid,   carbonic 
acid,  chlorine. 

c.  Mechanically  suspended  Matters :  Clay,  &c. 

We  confine  ourselves,  therefore,  here  to  the  estimation  of 
these  bodies. 

I.  The  Water  is  clear. 

1.  Determination  of  the  Chlorine. — This  may  be  effected, 
either,  a,  in  the  gravimetric,  or,  b.  in  the  volumetric  way. 

a.  Gravimetrically. 

Take  500 — 1000  grm.  or  c.  c.f  Acidify  with  nitric  acid,  and 
precipitate  with  silver  nitrate.  Filter  when  the  precipitate  has 
completely  subsided  (§  141,  I.,  a).  If  the  quantity  of  the  chlorine 
is  so  inconsiderable  that  the  solution  of  silver  nitrate  produces 
only  a  slight  turbidity,  evaporate  a  larger  portion  of  the  water  to 
i>  i>  i>  &c->  °f  its  bulk,  filter,  wash  the  precipitate,  and  treat  the 
filtrate  as  directed. 

b.  Yolumetrically. 

Evaporate  1000  grm.  or  c.  c.  to  a  small  bulk,  and  determine 
the  chlorine  in  the  residual  fluid,  without  previous  filtration,  by 
solution  of  silver  nitrate,  with  addition  of  potassium  chromate 
(§  141,  L,  8.  «). '  . 

*  Compare  Qualitative  Analysis,  p.  320  et  seq.  See  a  paper  recently  read 
before  the  Chemical  Society  by  Dr.  Miller— the  Society's  Journal  (2),  iii.  117  et 
seq.;  also,  Frankland,  idem (2),  iv.  239,  and  vi.  77;  and  Wanklyn,  Chapman, 
and  Smith,  idem,  vi.  152. 

f  As  the  specific  gravity  of  fresh  water  differs  but  little  from  that  of  pure 
water,  the  several  quantities  of  water  may  safely  be  measured  instead  of 
weighed.  The  calculation  is  facilitated  by  taking  a  round  number  of  c.  c. 


670  SPECIAL   PART.  [§  190. 

2.  Determination  of  the  Sulphuric  Acid. — Take  1000  grm.  or 
c.  c.      Acidify   with    hydrochloric    acid    and   mix   with   barium 
chloride.     Filter   after   the    precipitate    has   completely   subsided 
(§  132,  I.,  1).     If  the  quantity  of  the  sulphuric  acid  is  very  incon- 
siderable, evaporate  the  acidified  water  to  £,  J,  -J,  &c.,  of  the  bulk, 
before  adding  the  barium  chloride. 

3.  Determination  of  Nitric  Acid. — If,  on  testing  the  residue 
on  evaporation  of  a  water  for  nitric  acid,  such  a  strong  reaction  is 
obtained  that  the  presence  of  a  determinable  quantity  of  the  acid 
may  be  inferred,  evaporate  according  to  the  apparent  quantity  of 
nitric  acid  indicated  by   qualitative  testing  500  to  1000  or  2000 
c.  c.  of  the  water  in  a  porcelain  dish,  wash  the  residue  into  a  flask 
(it  is  immaterial  whether  any  solid  matter  which-  may  have  sepa- 
rated goes  partially  or  not  at  all  into  the  , flask),  evaporate  in  the 
flask   still   further,  if   necessary,  and   in   the    small   quantity   of 
residual  fluid  determine  the  nitric  acid  according  to  §  149,  d,  fi. 

4.  Determination   of  the  /Silicic  Acid,  Calcium,  and    Mag- 
nesium. 

Evaporate  1000  grm.  or  c.  c.  to  dryness — after  addition  of 
some  hydrochloric  acid — preferably  in  a  platinum  dish,  treat  the 
residue  with  hydrochloric  acid  and  water,  filter  off  the  separated 
silicic  acid,  and  treat  the  latter  as  directed  §140,  II.,  a.  Deter- 
mine calcium  and  magnesium  in  the  filtrate  aS  directed  §  154,  6, 
a  (28). 

5.  Determination  of  the  total  Residue  and  of  the  Sodium. 

a.  Evaporate  1000  grm.  or  c.  c.  of  the  water,  with  proper  care, 
to  dryness  in  a  weighed  platinum  dish,  first  over  a  lamp,  finally 
on  the  water-bath.  Expose  the  residue,  in  the  air-bath,  to  a 
temperature  of  about  180°,  until  no  further  diminution  of  weight 
takes  place.  This  gives  the  total  amount  of  the  salts. 

1).  Treat  the  residue  with  water,  and  add,  cautiously,  pure 
dilute  sulphuric  acid  in  moderate  excess ;  cover  the  vessel  during 
this  operation  with  a  dish,  to  avoid  loss  from  spirting ;  then  place 
on  the  water-bath,  without  removing  the  cover.  After  ten  minutes, 
rinse  the  cover  by  means  of  a  washing  bottle,  evaporate  the  con- 
tents of  'the  dish  to  dryness,  expel  the  free  sulphuric  acid,  ignite 
the  residue,  in  the  last  stage  with  addition  of  some  ammonium  car- 
bonate (§  97,  1),  and  weigh.  The  residue  consists  of  sodium  sul- 
phate, calcium  sulphate,  magnesium  sulphate,  and  some  separated 


§  190.]  ANALYSIS   OF   FKESH   WATER.  671 

silica.  It  must  not  redden  moist  litmus  paper.  The  quantity  of 
the  sodium  sulphate  in  the  residue  is  now  found  by  subtracting 
from  the  weight  of  the  latter  the  known  weight  of  the  silica  and 
the  weight  of  the  calcium  and  magnesium  sulphates  calculated 
from  the  quantities  of  these  earths  found  in  4. 

6.  Direct  Determination  of  the  Sodium. 

The  sodium  may  also  be  determined  in  the  direct  way,  with 
comparative  expedition,  by  the  following  method : — 

Evaporate  1250  gnn.  or  c.  c.  of  the  water,  in  a  dish,  to  about  ^, 
and  then  add  2 — 3  c.  c.  of  thin  pure  milk  of  lime,  so  as  to  impart 
a  strongly  alkaline  reaction  to  the  fluid  ;  heat  for  some  time  longer, 
then  wash  the  contents  of  the  dish  into  a  quarter-litre  flask.  (It  is 
not  necessary  to  rinse  every  particle  of  the  precipitate  into  the 
flask ;  but  the  whole  of  the  fluid  must  be  transferred  to  it,  and  the 
particles  of  the  precipitate  adhering  to  the  dish  well  washed,  and 
the  washings  also  added  to  the  flask.)  Allow  the  contents  to  cool,v 
dilute  to  the  mark,  shake,  allow  to  deposit,  filter  through  a  dry  filter, 
measure  off  200  c.  c.  of  the  filtrate,-  corresponding  to  1000  grm.  of 
the  water,  transfer  to  a  quarter-litre  flask,  mix  with  ammonium  car- 
bonate and  some  ammonium  oxalate,  add  water  up  to  the  mark, 
shake,  allow  to  deposit,  filter  through  a  dry  filter,  measure  off  200 
c.  c.,  corresponding  to  800  grm.  of  the  water,  add  some  ammonium 
chloride,*  evaporate,  ignite,  and  weigh  the  residual  sodium  chloride 
as  directed  §  98,  2.f 

Or  by  the  following  method : — 

Evaporate  the  filtrate  from  the  barium  sulphate  obtained  in  2 
to  dryness  in  a  platinum  dish  (or  if  nitrates  are  present  in  porcelain) 
to  remove  free  hydrochloric  acid  and  separate  silica.  Digest  the 
residue  with  a  few  c.  c.  water,  and  precipitate  magnesium  without 
previous  filtration  by  addition  of  solution  of  barium  hydroxide, 
avoiding  a  large  excess.  Enough  has  been  added  if  a  pellicle  of 
barium  carbonate  forms  upon  the  surface  of  the  liquid  on  exposure 
a  short  time  to  the  air.  Filter  and  wash  the  usually  slight  precipi- 
tate. Heat  the  filtrate,  and  add  ammonium  carbonate  to  precipitate 

*  To  convert  the  still  remaining  sodium  sulphate,  on  ignition,  into  sodium 
chloride.  • 

f  This  process,  which  entirely  dispenses  with  washing,  presents  one  source  of 
error — viz.,  the  space  occupied  by  the  precipitates  is  not  taken  into  account.  The 
error  resulting  from  this  is,  however,  so  trifling,  that  it  may  safely  be  disregarded, 
as  the  excess  of  weiht  amounts  to  -  at  the  most. 


672  SPECIAL   PART.  [§  190. 

the  barium  introduced  and  the  calcium  originally  present,  filter 
from  the  precipitated  carbonates,  and  evaporate  the  filtrate  to  dry- 
ness,  and  remove  by-  heating  the  ammonium  chloride  completely. 
Dissolve  the  sodium  chloride  in  the  residue  with  4  or  5  c.  c.  water, 
warm,  and  add  a  few  drops  of  ammonium  carbonate  and  ammonia  to 
separate  possibly  remaining  traces  of  barium  and  calcium,  filter  again 
into  a  weighed  platinum  dish,  evaporate  to  dryness,  heat  nearly  to 
fusion,  and  weigh  the  sodium  chloride.  The  sodium  chloride 
obtained  by  either  process  will  contain  the  potassium  (as  chloride) 
if  any  is  present  in  the  water.  If  enough  alkali  chloride  is  obtained 
it  may,  after  weighing,  be  examined  for  potassium  according  to 
§  152,  1,  a. 

7.  Calculate  the  numbers  found  in  1 — 6  to  1000  parts  of  water, 
and  determine  from  the  data  obtained  the  amount  of  carbonic  acid 
in  combination,  as  follows  : — 

Add  together  the  quantities  of  SO3  corresponding  to  the 
basic  oxides  found,  and  subtract  from  the  sum,  first,  the  amount  of 
sulphuric  acid  SO3  precipitated  from  the  water  by  barium  chloride 
(2),  secondly,  the  amount  equivalent  to  the  nitric  acid  found,  aird 
thirdly,  the  amount  equivalent  to  the  chlorine  found ;  the  remain- 
der is  equivalent  to  the  carbonic  acid  combined  with  the  bases  in 
the  form  of  normal  carbonates.  80  parts  of  SO3  remaining  after  sub- 
tracting the  quantities  just  stated,  correspond  accordingly  to  44 
parts  of  CO2. 

If,  by  way  of  control,  you  wish  to  determine  the  combined  car- 
bonic acid  in  the  direct  way,  evaporate  1000  grm.  or  c.  c.  of  the 
water,  in  a  flask,  to  a  small .  bulk ;  add  tincture  of  cochineal,  then 
standard  nitric  acid,  and  proceed  as  directed  p.  698. 

8.  Control. 

If  the  quantities  of  the  ^"a2O,  CaO,  MgO,  SO3,  NaO6,  SiO2,  CO, 
and  Cl  are  added  together,  and  an  amount  of  oxygen  equivalent  to 
the  chlorine  (since  this  latter  is  combined  with  metal  and  not  with 
oxide)  is  subtracted  from  the  sum,  the  remainder  must  nearly 
correspond  to  the  total  amount  of  the  salts  found  in  5,  a.  Perfect 
correspondence  cannot  be  expected,  since,  1,  upon  the  evaporation 
of  the  water  magnesium  chloride  is  partially  decomposed,  and  con- 
verted into  a  basic  salt;  2,  the -silicic  acid  expels  some  carbonic 
acid ;  and  3,  it  being  difficult  to  free  magnesium  carbonate  from 
water  without  incurring  loss  of  carbonic  acid,  the  residue  remain- 
ing upon  the  evaporation  of  the  water  contains  the  magnesium 


§  190.]  ANALYSIS    OF   FRESH   WATEE.  673 

carbonate  as  a  basic  salt,  whereas,  in  our  calculation,  we  have 
assumed  the  quantity  of  carbonic  acid  corresponding  to  the  normal 
salt. 

9.  Determination  of  the  free  Carbonic  Acid.    ' 

In  the  case  of  well-water  this  may  be  conveniently  executed 
by  the  process  described  §  139,  /3  (p.  405).  We  here  obtain  the 
carbonic  acid  which  is  contained  in  the  water  over  and  above  the 
quantity  corresponding  to  the  normal  carbonates,  or  in  other  words, 
the  carbonic  acid  which  is  free  and  which  is  combined  with  the 
carbonates  to  bicarbonates. 

10.  Determination  of  the  Organic  Matter. 

Many  fresh  waters  contain  so  much  organic  matter  as  to  be 
quite  yellow,  others  contain  traces,  and  many  again  may  be  said  to 
be  free  from  such  substances.  The  exact  estimation  of  organic 
matter  is  by  no  means  an  easy  task,  and  the  method  usually 
adopted — viz.,  ignition  of  the  residue  of  the  water  dried  at  180°, 
treatment  with  ammonium  carbonate,  gentle  ignition  again,  and 
calculation  of  the  organic  matter  from  the  loss  of  weight — yields 
merely  an  approximate  result,  since  we  can  never  be  sure  as  to  the 
condition  of  the  magnesium  carbonate  in  the  residue  dried  at 
180°  and  in  the  same  after  ignition,  and  since  the  silicic  acid  expels 
some  carbonic  acid,  which  is  not  taken  up  again  on  treatment  with 
ammonium  carbonate,  &c. 

[This  approximation,  however,  will  generally  suffice,  if  the 
purpose  of  the  analysis  is  to  enable  one  to  judge  of  the  quality 
of  the  water  with  reference  to  its  use  in  steam-boilers  and  for 
most  manufacturing  processes.  But  if  it  is  desired  to  learn 
by  analysis  whether  the  water  is  fit  or  unfit  for  drinking,  the 
case  is  quite  different,  for  its  quality  as  a  potable  water  doubt- 
less depends  greatly  on  the  amount,  and  still  more  on  the  kind,  of 
organic  matter  present.  Detailed  descriptions  of  methods  used  in 
the  examination  of  the  organic  matter  contained  in  water  are  to  be 
found  in  «  Water  Analysis,"  by  J.  A.  WAKKLYN  and  E.  T.  CHAP- 
MAX,  third  edition,  London,  Truebner  &  Co.,  1874: ;  Anleitung  znr 
Untersuchung  von  Wasser,  von  Kubel  und  Tiemann,  2  Aufl. ;  also 
in  several  articles  on  the  subject  by  WANKLYN,  CHAPMAN,  and 
SMITH,  in  Journal  of  the  Chem.  Soc.] 
II.  The  ivater  is  not  clear. 

Fill  a  large  flask  of  known  capacity  with  the  water,  close  with 


674  SPECIAL   PAKT.  [§  190. 

a  glass  stopper,  and  allow  the  flask  to  stand  in  the  cold  until  the 
suspended  matter  is  deposited;  draw  off  the  clear  water  with  a 
siphon  as  far  as  practicable,  filter  the  bottoms,  dry  or  ignite  the 
contents  of  the  filter,  and  weigh.  Treat  the  clear  water  as  directed 
in  I. 


Eespecting  the  calculation  of  the  analysis,  I  remark  simply  that 
the  results  are  usually*  arranged  upon  the  following  principles  :— 

The  chlorine  is  combined  with  sodium ;  if  there  is  an  excess, 
this  is  combined  with  calcium.  If,  on  the  other  hand,  there 
remains  an  excess  of  sodium,  this  is  combined  with  sulphuric  acid. 
The  sulphuric  acid,  or  the  remainder  of  the  sulphuric  acid,  as  the 
case  may  be,  is  combined  with  calcium.  The  nitric  acid  is,  as  a 
rule,  to  be  combined  with  calcium.  The  silicic  acid  is  put  down 
in  the  free  state,  the  remainder  of  the  calcium  and  the  magnesium 
as  carbonates,  either  normal  or  acid,  according  to  circumstances. 

It  must  always  be  borne  in  mind  that  the  results  of  the  qualita- 
tive analysis  may  render  another  arrangement  of  the  acids  and 
bases  necessary.  For  instance,  if  the  evaporated  water  reacts 
strongly  alkaline,  sodium  carbonate  is  present,  generally  in  com- 
pany with  sodium  sulphate  and  sodium  chloride,  occasionally  also 
with  sodium  nitrate.  The  calcium  and  magnesium  are  then  to  be 
entirely  combined  with  carbonic  acid. 

In  the  report,  the  quantities  are  represented  in  parts  per  1000 
(or  1000,000),  and  also  in  grains  per  gallon. 


For  technical  purposes,  it  is  sometimes  sufficient  to  estimate  the 
hardness  of  the  water  (the  relative  amount  of  calcium  and  magne- 
sium in  it)  by  means  of  a  standard  solution  of  soap.  A  detailed 
description  of  this  method,  which  was  first  employed  by  CLAEK, 
may  be  found  in  BOLLEY  &  PAUL'S  Handbook  of  Technical 
Analysis.  See  also  STJTTON'S  Yolumetric  Analysis. 

*  A  certain  latitude  is  here  allowed  to  the  analyst's  discretion 


§  192.]  ACIDIMETRY.  675 

2.  ACIDIMETKY. 

A.  ESTIMATION  BY  SPECIFIC  GRAVITY. 
§191. 

Tables,  based  upon  the  results  of  exact  experiments,  have  been 
drawn  up,  expressing  in  numbers  the  relation  between  the  specific 
gravity  of  the  aqueous  solution  of  an  acid,  and  the  amount  of  real 
acid  contained  in  it.  Therefore,  to  know  the  amount  of  real  acid 
contained  in  an  aqueous  solution  of  an  acid,  it  suffices,  in  many 
cases,  simply  to  determine  its  specific  gravity.  Of  course  the  acids 
must,  in  that  case,  be  free,  or  at  least  nearly  free  from  admixtures 
of  other  substances  dissolved  in  them.  Now,  as  most  common 
acids  are  volatile  (sulphuric  acid,  hydrochloric  acid,  nitric  acid, 
acetic  acid),  any  non-volatile  admixture  may  be  readily  detected  by 
evaporating  a  sample  of  the  acid  in  a  small  platinum  or  porcelain 
dish. 

The  determination  of  the  specific  gravity  is  effected  either  by 
comparing  the  weight  of  equal  volumes  of  water  and  acid,  or  by 
means  of  a  good  hydrometer.  The  estimations  must,  of  course,  be 
made  at  the  temperature  to  which  the  Tables  refer. 

The  following  Tables  on  pages  676 — 679  give  the  relations 
between  the  specific  gravity  and  the  strength  for  sulphuric  acid, 
hydrochloric  acid,  nitric  acid,  and  acetic  acid. 

In  all  cases  in  which  the  determination  of  the  specific  gravity 
fails  to  attain  the  end  in  view,  or  which  demand  particular  accuracy, 
the  volumetric  method  described  under  B,  is  employed. 

B.  ESTIMATION   BY    SATURATION   WITH    AN   ALKALINE    FLUID    OF 

KNOWN    STRENGTH.* 

§192. 

1.  This  method  requires : — 

A  dilute  acid  of  known  strength.  Sulphuric  or  hydrochloric 
acid  may  be  used.  Nitric  and  oxalic  acids  are  less  frequently 
employed. 

*  According  to  NICHOLSON  and  PRICE  (Chem.  Gaz.,  1856,  p.  30)  the  common 
method  of  acidimetry  is  not  suited  for  determining  free  acetic  acid,  on  account 
of  the  alkaline  reaction  of  neutral  sodium  acetate;  however,  OTTO  (Annal.  d. 
Chem.  u.  Pharm.  102,  69)  has  clearly  demonstrated  that  the  error  arising  from 
this  is  so  inconsiderable  that  it  may  safely  be  disregarded. 


676 


SPECIAL   PART. 


[§  192. 


TABLE  I. 

Showing  the  percentages  of  Acid  (H28O4)  and  Anhydride  (SO3)  corresponding  to 
vari&us  specific  gravities  of  aqueous  Sulphuric  Acid  by  BINEAU  ;  calculated  for 
15°,  by  OTTO. 


Specific 
gravity. 

Percentage        Percentage 
ofH2SO4.            ofSO3. 

Specific 
gravity. 

Percentage 
of  H2SO4. 

Percentage 
of  S03. 

1  8426               100 

81-63 

1-398 

50 

40-81 

1-842                  99 

80-81 

1-3886 

49 

40-00 

1-8406                 98 

80-00 

1-379 

48 

39-18 

1-840                  97 

79-18 

1-370 

47 

38-36 

1-8384                96 

78-36 

1-361 

46 

37-55 

1-8376                95 

77-55 

1-351 

45 

36-73' 

1-8356 

94 

76-73 

1-342 

44 

35-82 

1-834 

93 

75-91 

1-333 

43 

35-10 

1-831 

92 

75-10 

1-324 

42 

34-28 

1-827 

91 

74-28 

1-315 

41 

33-47 

1-822 

90 

73-47 

1-306 

40 

32-65 

1-816 

89 

72-65 

1-2976 

39 

31-83 

1-809 

88 

71-83 

1-289 

38 

31-02 

1-802 

87 

71-02 

1-281 

37 

30-20 

1-794 

86 

70-10 

1-272 

36 

29  38 

1-786 

85 

69-38 

1-264 

35 

28-57 

1-777 

84 

68-57 

1-256 

34 

.   27-75 

1-767 

83 

67-75 

1-2476 

33 

26-94 

1-756 

82 

66-94 

1-239 

32 

26-12 

1-745 

81 

66-12 

1-231 

31 

25-30 

1-734 

80 

65-30 

1-223 

30 

34-49 

1-722 

79 

64-48 

1-215 

29 

23-67 

1-710 

78 

63-67 

1-2066 

28 

22-85 

1-698 

77 

62-85 

1-198 

27 

22-03 

1-686 

76 

62-04 

1-190 

26 

21-22 

1-675 

75 

61-22 

1-182 

25 

20  40 

1-663 

74 

60-40 

1-174 

24 

19-58 

1-651 

73 

59'59 

1-167 

23 

18-77 

1-639 

72 

58-77 

1-159 

22 

17-95 

1-627 

71 

57-95 

1-1516 

21 

17-14 

1-615 

70 

57-14 

1-144 

20 

16-32 

1-604 

69 

56-32 

1-136 

19 

15-51 

1-592 

68 

55-59 

1-129 

18 

14-69 

1-580 

67 

54-69 

1-121 

17 

13-87 

1-568 

66 

53-87 

1-1136 

16 

13-06 

1-557 

65 

53-05 

1-106 

15 

12-24 

1-545 

64 

52-24 

1-098 

14 

11-42 

1-534 

63 

51-42 

1-091 

13 

10-61 

1-523 

62 

50-61 

1-083 

12 

9-79 

1-512 

61 

49-79 

1-0756 

11 

8-98 

1-501 

60 

48-98 

1-068 

10 

8-16 

1-490 

59 

48-16 

1-061 

9 

7-34 

1-480 

58 

47-34 

1-0536 

8 

6-53 

1-469 

57 

46-53 

1-0464 

7 

5-71 

1-4586 

56 

45-71 

1-039 

6 

4-89 

1-448 

55 

44-89 

1-032 

5 

4-08 

1-438 

54 

44-07 

1-0256 

4 

3-26 

1-428 

53 

43-26 

1-019 

3 

2-445 

1-418 

52 

42-45 

1-013 

2 

1-63 

1-408 

51 

41-63 

1-0064 

1 

0-816 

192.] 


ACH)IMETBT. 


677 


TABLE  II. 

Sliowing  the  percentages  of  Anhydrous  Acid  (HC1 )  corresponding  to  various  specific 
gravities  of  Uqueous  solutions  of  Hydrochloric  Acid,  by  UBE.  Tempera- 
ture 15°. 


Specific  gravity. 

Percentage  of 
hydrochloric  acid  gas 
(HC1). 

Specific  gravity. 

Percentage  of 
hydrochloric  acid  gas 
(HC1). 

1-2000 

40-777 

1-1000 

20-388 

1-1982 

40-369 

1-0980 

19-980 

1-1964 

39-961 

1-0960 

19-572 

1-1946 

39-554 

1-0939 

19-165 

1-1928 

39-146 

1-0919 

18-757 

1-1910 

38-738 

1-0899 

18-349 

1-1893 

38-330 

1-0879 

17-941 

1-1875 

37-923 

1-0859 

17-534 

1-1857 

37-516 

1-0838 

17-126 

1-1846 

37-108 

1-0818 

16-718 

1-1822 

36-700 

1-0798 

16-310 

1-1802 

36-292 

1-0778 

15-902 

1-1782 

35-884 

1-0758 

15-494 

1-1762 

35-476 

1-0738 

15-087 

1-1741 

35-068 

1-0718 

14-679 

1-1721 

34-660 

1-0697 

14-271 

1-1701 

34-252 

1-0677 

13-863 

1-1681 

33-845 

1-0657 

13-456 

1-1661 

33-437 

1-0637 

13-049 

1-1641 

33-029 

1-0617 

12-641 

1-1620 

32-621 

1-0597 

12-233 

1-1599 

32-213 

1-0577 

11-825 

1-1578 

31-805 

1-0557 

11-418 

1-1557 

31-398 

•0537 

11-010 

1-1537 

30-990 

•0517 

10-602 

1-1515 

30-582 

•0497 

10-194 

1-1494 

30-174 

•0477 

9-786 

1-1473 

29-767 

•0457 

9  379 

1-1452 

29-359 

•0437 

8-971 

1-1431 

28-951 

1-0417 

8-563 

1-1410 

28-544 

1-0397 

8-155 

1-1389 

28-136 

1-0377 

7-747 

1-1369 

27-728 

1-0357 

7-340 

V1349 

27-321 

1-0337 

6-932 

1-1328 

26-913 

1-0318 

6-524 

1-1308 

26  505 

1-0298 

6-116 

1-1287 

26-098 

1-0279 

5-709 

1-1267 

25-690 

1-0259 

5-301 

1-1247 

25-282 

1-0239 

4-893 

1-1226 

24-874 

1-0220 

4-486 

1-1206 

24-466 

1-0200 

4-078 

1-1185 

24-058 

1-0180 

3-670 

1-1164 

23-650 

1-0160 

3-262 

1-1143 

23-242 

1-0140 

2-854 

1-1123 

22-834 

1-0120 

2-447 

1-1102 

22-426 

1-0100 

2-039 

1-1082 

22-019 

1-0080 

1-631 

1-1061 

21-611 

1-0060 

1-124 

1-1041 

21-203 

1-0040 

0-816 

1  1020 

20-796 

1-0020 

0-408 

678 


SPECIAL  PAKT. 


[§  192. 


TABLE  III. 

Showing  the  percentages  of  Nitric  Anhydride   (N2  O5)  corresponding  to  various 
specific  gvavities  of  aqueous  Nitric  Acid,  by  URE.     Temperature  15°. 


Specific 
gravity. 

Percentage 
of  NaO5. 

Specific 
gravity. 

Percentage 
of  N8O5. 

Specific 
gravity. 

Percentage 
of  Na06. 

Specific 
gravity. 

Percentage 
of  NaO6. 

1-500 

79-7 

1-419 

59-8 

1-295 

39-8 

1-140 

19-9 

1-498 

78-9 

1-415 

59-0 

1-289 

39-0 

1-134 

19-1 

1-496 

78-1 

1-411 

58-2 

•283 

38-3 

1-129 

18-3 

1-494 

77-3 

1-406 

57-4 

•276 

37-5 

1-123 

17-5 

1-491 

76-5 

1-402 

56-6 

•270 

36-7 

1-117 

16-7 

1-488 

75-7 

1-398 

55-8 

•264 

35-9 

1-111 

15-9 

1-485 

74-9 

•394 

55-0 

•258 

35-1 

1-105 

15-1 

1-482 

74-1 

.     -388 

54-2 

•252 

34-3 

1-099 

14-3 

1-479 

73  3 

•383 

53-4 

1-246 

33-5 

1-093 

13-5 

1-476 

72-5 

•378 

52-6 

1-240 

32-7 

1-088 

12-7 

1-473 

71-7 

•373 

51-8 

1-234 

31-9 

1-082 

11-9 

1-470 

70-9 

•368 

51-1 

1-228 

31-1 

1-076 

11-2 

1-467 

70-1 

1-363 

50  2 

1-221 

30-3 

1-071 

10-4 

1-464 

69-3 

1-358 

49-4 

1  215 

29-5 

1-065 

9-6 

1-460 

68-5 

1-353 

48'6 

1  208 

28'7 

1-059 

8-8 

1-457 

67-7 

1-348 

47-9 

1-202 

27'9 

1-054 

8-0 

1-453 

66-9 

•343 

47-0 

1-196 

27-1 

1-048 

7-2 

1-450 

66-1 

•338 

46-2 

1-189 

26-3 

1-043 

6-4 

1-446 

65-3 

•332 

45-4 

1-183 

25'5 

1-037 

5-6 

1-442 

64-5 

•327 

44-6 

1-177 

24-7 

1-032 

4-8 

1-439 

63-8 

•322 

43-8 

1-171 

23-9 

1-027 

4-0 

1-435 

63-0 

•316 

43-0 

1-165 

23-1 

1-021 

3-2 

1-431 

62-2 

1-311 

42-2 

1-159 

22-3 

1-016 

2-4 

1-427 

61-4 

1-306 

41-4 

1  153 

21-5 

1-011 

1-6 

1-423 

60-6 

1-300 

40-4 

1-146 

20-7 

1-005 

0-8 

2.  An  alkaline  fluid  of  known  strength.  Potassa  or  ammonia 
may  be  employed. 

a.  PREPARATION  OF  THE  SOLUTIONS. 

The  solutions  should  be  of  suitable  strength.  As,  the  first 
step  in  the  preparation  of  a  dilute  sulphuric  acid,  of  convenient 
strength  for  ordinary  use,  dilute  20  cubic  centimetres  of  oil  of  vit- 
riol with  water  to  the  volume  of  2  litres. 

The  standard  alkali  is  made  from  commercial  caustic  potash ; 
this  is  dissolved  in  water  and  diluted  until  a  given  volume,  e.g.,  5. 
c.  c.,  neutralizes  4  to  5  c.  c.  of  the  standard  acid,  as  is  determined 
by  a  few  rough  trials. 

The  alkali  solution  thus  obtained  is  heated  to  boiling  in  a  flask, 
and  a  little  freshly-slaked  lime  is  added  to  decompose  any  potas- 
sium carbonate.  The  boiling  is  continued  a  few  minutes  and. 


§  192.] 


ACIDIMETRY. 


679 


TABLE  IV. 

Sliowing  the  percentages  of  Acetic    Acid  (HC3H3O?)  corresponding  to   various 
specific  gravities  of  aqueous  solutions  of  Acetic  Acid,  by  MOHK. 


Specific 
.gravity. 

Sa-j 
§3° 

c-HK 

Specific 
gravity. 

111 

|£« 

Specific 
gravity. 

fe 

c.2W 

Specific 
gravity. 

m 
10 

Specific 
gravity. 

2s-* 

|i°. 

If* 

li§ 

g«S 

ll« 

fig 

!& 

1-0635 

100 

'  1-0735 

80     ' 

1-067 

60 

1-051 

40 

1-027 

20 

1-0555 

99 

1-0735 

79 

1-066 

59 

1-050 

39 

1-026 

19 

1-0670 

98 

1-0732 

78 

1-066 

58    ; 

1-049 

38 

1-025 

18 

1-0680 

97 

1-0732 

77 

1-065 

57 

1-048 

37 

1-024 

17 

1-0690 

96 

1-0730 

76 

1-064 

56 

1-047 

36 

1-023 

16 

1-0700 

95 

1-0720 

75 

•064 

55 

1-046 

35 

1-022 

15 

1-0706 

94 

!  1-0720 

74 

•063 

54 

1-045 

34 

1-020 

14 

1-0708 

93 

1-0720 

73 

•063 

53 

1-044 

33 

1-018 

13 

1-0716 

92 

i  1-0710 

72 

•062 

52 

1-042 

32 

1-017 

12 

1-0721 

91 

1-0710 

71 

•061 

51 

1-041 

31 

1-016 

11 

1-0730 

90 

1-0700 

70 

•060 

50 

1-040 

30 

1-015 

10 

1-0730 

89 

1-0700 

69 

•059 

49 

1-039 

99 

1-013 

9 

1-0730 

88 

1-0700 

68 

•058 

48 

•088 

28 

1-012 

8 

1-0730 

87 

1-0690 

67 

•056 

47 

•036 

27 

1-010 

7 

1-0730 

86 

1-0690 

66 

1-055 

46 

•035 

26 

1-008 

6 

1-0730 

85 

1-0680 

65 

1-055 

45 

•034 

25 

1-007 

5 

1-0730 

84 

1-0680 

64 

1-054 

44 

•033 

24 

1-005 

4 

1-0730 

83 

1-0680 

63 

1-053 

43 

•032 

23 

1-004 

3 

1-0730 

82 

1-0670 

62 

1-052 

42 

•031 

22 

1-002 

2 

1-0732 

81 

1-0670 

61 

1-051 

41 

1-029 

21 

1-001 

1 

1 

finally,  the  lye  is  poured  upon  a  filter,  and  the  filtrate  is  collected 
in  the  bottle  from  which  it  is  to  be  used.  Care  should  be  taken 
to  bring  upon  the  filter  some  of  the  excess  of  lime  that  is  suspended 
in  the  liquid,  so  that  the  latter  may  acquire  no  carbonic  acid  from 
the  air.  This  clear  liquid  thus  obtained  is  a  potash-lye  containing 
lime  in  solution.  If  exposed  to  the  air,  the  carbonic  acid  that  is 
absorbed  separates  as  calcium  carbonate,  leaving  the  liquid  per- 
fectly caustic. 

It  now  remains  to  determine  with  the  greatest  accuracy,  1st, 
the  volume  of  alkali  which  neutralizes  a  cubic  centimetre  of  the 
acid,  and,  2d,  the  amount  of  SO3  contained  in  a  cubic  centimetre 
of  the  latter. 

As  a  means  of  recognizing  the  point  of  neutralization,  tincture 
of  cochineal  possesses  great  advantages  over  solution  of  litmus. 
The  knowledge  of  this  fact  is  due  to  LUCKOW,  who  has  detailed  its 
application  in  Joum.fiir  prakt.  Chem.,  Ixxxiv.  p.  424.  Tincture 


680  SPECIAL   PART.  [§  192. 

of  cochineal  is  prepared  by  digesting  and  frequently  agitating  three 
grammes  of  pulverized  cochineal  in  a  mixture  of  50  cubic  centi- 
metres of  strong  alcohol  with  200  c.  c.  of  distilled  water,  at  ordinary 
temperatures,  for  a  day  or  two.  The  solution  is  decanted,  or  fil- 
tered through  Swedish  paper. 

The  tincture  thus  prepared  has  a  deep  ruby-red  color.  On 
gradually  diluting  with  pure  water  (free  from  ammonia),  the  color 
becomes  orange  and  finally  yellowish-orange.  Alkalies  and  alkali- 
earths  as  well  as  their  carbonates  change  the  color  to  a  carmine  or 
violet-carmine.  Solutions  of  strong  acid  and  acid  salts  make  it 
orange  or  yellowish-orange. 

•  To  determine  the  volumetric  relation  of  the  alkali  and  acid,  a 
given  volume  of  the  latter,  e.g.,  20  c.  c.,  is  measured  off  into  a  wide- 
mouthed  flask,  10  drops  of  cochineal-tincture,  and  about  150  c.c. 
of  water  are  added  ;  the  alkali  is  now  allowed  to  flow  in  from  a 
burette,  until  the  yellowish  liquid  in  the  flask,  suddenly,  and  by  a 
single  drop,  acquires  a  violet-carmine  tinge. 

In  nicer  determinations,  it  is  important  to  bring  the  liquid  each 
time  to  a  given  volume,  by  adding  water  after  the  neutralization 
is  nearly  finished.  For  this  purpose,  two  or  more  flasks  of  equal 
capacity  are  selected,  and  on  the  outside  of  each  a  strip  of  paper  is 
gummed  to  indicate  the  level  of  the  proper  amount  of  liquid,  e.g., 
200  c.  c.  The  same  amount  of  coloring  matter  being  thus  always 
diffused  in  the  same  volume  of  the  same  water,  the  errors  of  vary- 
ing dilution  and  varying  amount  of  ammonia  (which  is  rarely 
absent  from  distilled  water)  are  avoided.  The  contents  of  one 
flask,  in  which  the  neutralization  has  been  satisfactorily  effected, 
may  be  kept  as  a  standard  of  color  for  the  succeeding  trials,  as  the 
tint  remains  constant  for  hours,  being  unaffected  by  the  absorption 
of  carbonic  acid.  The  greatest  convenience  and  accuracy  of  mea- 
surement' are  obtained  by  using  burettes  provided  with  EKDMANN'S 
swimmer  (see  p.  40). 

When  three  or  four  accordant  results  have  been  obtained,  the 
average  is  taken  as  expressing  the  relative  strength  of  the  acid  and 
alkali. 

To  ascertain  the  absolute  standard,  weigh  off  in  a  small  plati- 
num crucible  about  0'8  grm.  of  pure  sodium  carbonate,  ignite  to 
dull  redness,  cool  and  weigh  accurately :  bring  the  crucible  with 
its  contents  into  one  of  the  wide-mouthed  flasks  and  let  flow  from 
the  burette  a  slight  excess,  e.g.  50  c.  c.,  of  standard  acid.  The  solu- 


§  192.]  ACIDIMETRY.  681 

tion  of  sodium  carbonate  is  facilitated  by  wanning,  and,  finally,  the 
contents  of  the  flask  are  gently  boiled  for  several  minutes  to  expel 
carbonic  acid.  The  solution  is  now  allowed  to  become  perfectly 
cold,  then  add  ten  drops  of  cochineal  and  lastly  the  standard  alkali 
to  neutralization,  diluting  to  the  proper  volume. 

To  illustrate  the  accuracy  of  the  process  and  the  calculations 
employed,  the  following  actual  data  may  be  useful.  The  acid  solu- 
tion was  made  by  diluting  50  c.  c.  of  oil  of  vitriol  to  the  volume  of 
ten  litres  and  had  half  the  strength  above  recommended.  The 
alkali  was  from  a  stock  on  hand  and  more  dilute  than  necessary. 


.Relation  of  acid  to  alkali. 

Exp.  L,  20  c.  c.  HaSO4  =  32-8  c.  c.  KOH,  or  1 
Exp.  II.,  20  c.  c.  HaSO4  =  32  •  8  c.  c.  KOH,  or  1 
Exp.  III.,  40  c.  c.  H3SO4  =  65-7  c.  c.  KOH,  or  1 


1-64 


1-6425. 


We  have  accordingly  : 

1  c.  c.  H3SO4  =  1-64  c.  c.  KOH  and  1  c.  c.  KOH  =  0-60976  c.  c. 

HaSO, 

Absolute  strength  of  acid  and  alkali. 

Exp.  I.  0*4:177  grin,  of  sodium  carbonate  were  treated  with 
44*2  c.  c,  of  HaSO4  solution.  To  neutralize  -the  excess  of  the  acid 
were  required  3'8  c.  c.  KOH,  which  correspond  to  2*32  c.  c.  HaSO4 
(3-8  X  0-60976).  Deducting  this  from  the  total  amount  of  acid 
(44.2  —  2*32)  we  have  41  '88  c.  c.  of  acid,  neutralized  by  the  sodium 
carbonate  taken. 

41-88  c.  c.  solution  of  HaSO4  =  0-4177  grm.  Ka,CO3. 
Exp.  II.     0.4126  grm.  Na.CO,  treated  with   44   c.  c.   HSSO4 
required  4*28  c.  c.  KOH.     4-28  X  0-60976  =  2'61  c.  c.  H3SO4.    44 
-  2-61  =  41-39  c.  c.  HaSO4. 

41-39  c.  c.  solution  of  H2SO4  =  0-4126  grm.  Na2CO3. 
Now,  from  the  data  obtained  by  each  of  these  experiments,  the 
absolute  strength  of  the  sulphuric  acid  solution  may  be  calculated  ; 
for  when  sodium  carbonate  and  sulphuric  acid  exactly  neutralize 
each  other,  one  molecule  or  106*08  pts.  ISTa2CO3  reacts  with  1 
molecule  or  98  pts.  HaSO4. 

mol.  weight  98        mol.  weight  106-08 


H2S04       -j         NaaC03         =  NaJS04  +  COa  +  HaO. 


682  SPECIAL   PART.  [§  192. 

Consequently  that  volume  of  a  sulphuric  acid  solution  which  is 
found  to  exactly  neutralize  1-0608  grm.  NaaCO3  must  contain  *98 
grm.  HJ30.. 

The  volume  of  the  sulphuric  acid  solution  in  the  present  case 
which  would  neutralize  1*0608  grm.  NaaCO3  is  found  by  calcula- 
tion from  the  data  furnished  by  the  experiments  to  be : — 

grms.  Na3CQ3          c.  c.  H2SO4  solution 


L,      -4177  :  1-0608  ::  41-88  :  106-35 
II.,     -4126  :  1-0608  ::  41-39  :  106-41 

According  to  Exp.  L,  106-35  c.  c.;  according  to  Exp.  II.,  106-41 
c.  c.  —  mean,  106-38  c.  c. 

This  volume  therefore  contains  *98  grm.  HaSO4.  By  dividing 
*98  grm.  by  106-38  the  weight  of  HaSO4  in  1  c.  c.  would  of  course 
be  found. 

But  the  already  found  volume  of  the  sulphuric  acid  which  con- 
tains a  weight  of  H2SO4  corresponding  to  its  molecular  weight  is  a 
more  convenient  basis  for  calculating  the  weight  of  any  alkali  neu- 
tralized by  1  c.  c.  Suppose  it  is  desired,  for  instance,  to  find  the 
weight  of  NH4OH,  XH3,  or  N  which  corresponds  to  1  c.  c.  of  the 
.acid  solution.  One  molecule  of  sulphuric  acid  neutralizes  2  mol. 


mol.  weight  98     mol.  weight  35  X  2  =  70 


HS04  2JSTHOH         =  (NE^JSO,  +  (H,O)a. 

Hence  106-38  c.  c.  =  -98  grm.  HaSO4  neutralize  -70  grm.  NH4OH, 
.and  further,  observing  that  35  parts  (1  mol.)  of  Mi4OH  contain 
14  pts.  1ST  or  17  NH3— 

I   I 

i; 

O    16 
35 
and  70  pts.  (2  mol.)  twice  these  quantities  — 

106  •  38  c.  c.  acid  solution  correspond  to  •  34  grm. 

"  "          "  «  "   .28     " 

Finally  find  the  weight  of  the  substance  which  corresponds  to 


§  192.]  ACIDIMETKY.  683 

1  c.  c.  of  the  standard  solution.  For  nitrogen,  e.g.,  this  is  '28  grin. 
-h  106-38  =  0-002632  grm. 

We  may  then  write  on  the  label  of  the  acid  bottle  the  follow- 
ing data  for  calculation  :  — 

1  c.  c.  KOH  =  0-60976  c.  c.  HaSO4, 
1  c.  c.  H,SO4  =  1-64  c.  c.  KOH, 
1  c.  c.  HaSO4  =  0-002632  grm.  K 

In  a  like  manner,  we  may  calculate  the  weight  of  any  base,  or 
any  constituent  part  of  a  base  corresponding  to  1  c.  c.  of  the  stan- 
dard acid,  being  careful  to  observe  whether  one  or  two  molecules 
of  the  base  are  neutralized  by  one  mol.  HaSO4. 

To  ascertain  the  absolute  strength  of  the  alkali  solution.  Is'o 
further  experimental  work  is  required  for  this  purpose.  For  since 
•98  grm.  H2SO4  neutralize  1*1226  grm.  KOH,  as  clearly  seen  from 
the  formulae  with  appended  molecular  weights  expressing  the 
reaction, 

mol.  weight  98     mol.  weight  5613  X  2=112  "26 

~H£04     V  2KOH  ~"=  KaSO4  +  (HaO)a, 

it  follows  that  a  volume  of  potash  solution  which  exactly  neutral- 
izes 106-38  c.  c.  sulphuric  acid  solution  (i.e.,  the  volume  already 
found  to  contain  -98  grm.  HaSO4)  must  contain  1-1226  grm.  KOH. 
This  volume  of  potash  solution  may  be  calculated  from  the  already 
determined  volumetric  relation  of  the  acid  and  alkali  solutions, 
viz.:  — 

1  c.  c.  H2SO4  sol.  =  1-64  c.  c.  KOH  sol. 
106-38  c.  c.  X  1-64  =  174-46  c.  c. 

Accordingly  174'46  c.  c.  potash  solution  contain  1-1226  grm.  KOH, 
or  112-26  centigrammes  a  number  equal  to  twice  the  number  which 
expresses  the  molecular  weight  of  KOH.  The  weight  of  any  acid 
neutralized  by  1  c.  c.  of  this  alkali  solution  may  now  be  readily 
calculated,  bearing  in  mind  that  2  mol.  KOH  neutralize  2  mol.  of 
any  monobasic  and  1  mol.  of  any  dibasic  acid.  For  hydrochloric 
acid,  e.g.  : 

mol.  weight  56-13  X  2  =  112-26  mol.  weight  36'46  X  2  =  72.92 


(KOH),  eutrali«  (HCl)a 


684  SPECIAL    PART.  [§  192. 

176-46  c.c.  sol.  =  1-1226  grm.  KOH  neutralize  '7292  grm.  HC1. 


I  c.c.  alkali  solution  =  -00418  grm.  HC1. 

b.  THE  ACTUAL  ANALYSIS.  It  is  only  necessary  to  weigh 
or  measure  off  the  acid  to  be  examined,  dilute  to  about  150  c.  c.  and 
ascertain  how  much  of  the  standard  alkali  is  required  for  its  neu- 
tralization, proceeding  just  as  detailed  for  ascertaining  the  volu- 
metric relation  of  the  acid  and  alkali  solutions.  It  is  best  to  use  for 
determination  a  quantity  which  will  require  15  to  30  c.  c.,  but  not 
over  a  burette  full  of  the  standard  alkali.  It  is  often  convenient 
in  case  of  strong  acids  to  weigh  off  about  five  times  the  amount 
required  for  a  single  trial,  dilute  to  exactly  500  c.  c.  and  make  two 
or  more  determinations,  using  for  each  100  c.  c. 

tx.  If  the  color  of  a  fluid  conceals  the  change  of  the  dissolved 
cochineal,  or  if  salts  of  iron  be  present,  we  use  red  litmus  or 
turmeric  paper  to  hit  the  point  of  neutralization,  i.e.,  we  add  alkali 
till  a  strip  of  test  paper  dipped  in  just  indicates  a  weak  alkaline 
reaction.  In  this  case  more  alkali  will  be  employed  than  when 
cochineal  can  be  used  in  solution,  and  in  exact  determinations  it 
may  be  worth  while  to  rectify  the  error  by  a  correction.  This  may 
be  done  by  taking  a  like  quantity  of  water  and  adding  alkali  solu- 
tion, till  the  fluid  just  gives  a  reaction  on  the  test  paper  in  ques- 
tion, as  strong  as  was  obtained  at  the  close  of  the  first  experiment. 
The  quantity  of  alkali  used  is,  of  course,  to  be  deducted  from  the 
quantity  employed  in  the  first  experiment. 

ft.  Determination  of  Acids  by  means  of  normal  sodium  car- 
bonate solution.  See  <?,  tf,  page  687. 

y.  Application  of  the  Acidimetric  principle  to  the  determina- 
tion of  combined  acids. 

The  acidimetric  principle  may  often  be  employed  also  for  the 
determination  of  acids  in  combination  with  bases,  if  solution  of 
soda  or  sodium  carbonate  precipitates  the  latter  completely,  and  in 
a  state  of  purity.  For  instance,  acetic  acid  in  iron  mordant,  or  in 
verdigris,  may  be  estimated  in  this  way,  by  the  following  process  : 
Precipitate  with  a  measured  quantity  of  standard  solution  of  soda 
or  sodium  carbonate  in  excess,  boil,  filter,  wash,  concentrate  the  fil- 


§  192.]  ACIIH3IETEY. 

trate  which  contaios  the  excess  of  alkali  used.  Determine  the  num- 
ber of  c.  c.  of  this  excess  by  means  of  standard  acid  solution.  Sub- 
tract the  number  of  c.  c.  thus  found  from  the  c.  c  of  soda  solution 
consumed  in  the  experiment ;  the  difference  expresses  the  quantity 
<of  soda  solution  neutralized  by  the  acid  contained  in  the  substance, 
in  combination  as  well  as  in  the  free  state.  Of  course,  correct 
results  can  be  expected  only  if  no  basic  salt  has  been  thrown  down 
by  the  soda  solution. 

d.  Determination  of  combined  acids  ly  Gibbs*  method.  See 
:§  149,  ii.,  c,  r,  p.  472.  ' 

c.  DEVIATIONS  FROM  THE  PRECEDING  METHOD. 

a.  Different  acids   and  alkalies  for  standard  solutions. 

Hydrochloric  may  be  used  instead  of  sulphuric  acid,  and 
ammonia  instead  of  potash  solution.  A  hydrochloric  acid  solu- 
tion containing  13  grm.  HC1  per  1000  c.  c.  will  have  about  the 
same  neutralizing  power  as  the  -sulphuric  acid  solution  recom- 
mended in  the  preceding  (made  by  diluting  20  c.  c.  oil  of  vitriol  to 
2000  c.  c.).  Find  the  specific  gravity  of  a  sample  of  pure  aqueous 
hydrochloric  acid  and  calculate  by  means  of  Table  II.,  page  677,  the 
volume  required  to  contain  13  grm.  HC1,  and  dilute  to  1000  c.  c. 
Prepare  the  ammonia  solution  by  diluting  pure  ammonia  solu- 
tion until  it  is  found  by  trial  with  a  few  c.  c.  that  it  neutralizes 
nearly  an  equal  volume  of  the  HC1  solution.  Ascertain  next  the 
exact  volumetric  relation  of  the  acid  to  alkali  solution  as  before 
directed. 

The  ammonia  should  be  nearly  or  quite  free  from  ammonium 
carbonate.  Ammonia  from  a  freshly  opened  bottle  which  gives  a 
very  slight  or  no  immediate  precipitate  with  calcium  chloride  is 
suitable. 

The  absolute  strength  of  both  solutions  may  be  found  by  the 
same  method  that  is  applied  to  sulphuric  acid  and  potash  solutions. 

To  insure  accuracy  it  is  well  also  to  determine  chlorine  in  the 
acid  solution  by  precipitation  with  silver  nitrate.  These  solutions 
affect  the  burettes  less  than  potash  and  sulphuric  acid  solutions, 
and  are  more  readily  prepared. 

ft.  Different  indicators.  Many  kinds  have  been  proposed. 
Litmus  solution  is  preferable  to  cochineal  when  organic  acids  or 
aluminium  salts  are  present.  Carbonic  acid,  however,  renders  the 


686  SPECIAL   PART.  [§  192. 

indication  which  it  affords  quite  indistinct,  while  it  interferes  with 
the  action  of  cochineal  far  less. 

y.  To  save  time  in  computations.  When  many  successive  deter- 
minations are  to  be  made,  it  is  convenient  to  have  an  alkali  solution 
that  will  neutralize  exactly  an  equal  volume  of  the  standard  acid 
solution.  This  may  be  obtained  as  follows  :  After  ascertaining  the 
volumetric  relation  of  the  two  solutions,  calculate  how  many  c.  c. 
of  water  must  be  added  to  the  stronger  to  make  equal  the  weaker ; 
e.g.,  if  1  c.  c.  acid  solution  =  1*132  c.  c.  alkali  solution,  -132  c.  c. 
water  must  be  added  to  each  c.  c.  of  the  acid  solution,  or  132  c.  c  to 
1000  c.  c.  Measure  accurately  1000  c.  c.  of  the  acid  solution  in  a 
litre  flask,  and  pour  it  into  a  dry  bottle  designed  for  keeping  the 
standard  solution,  then  measure  by  means  of  a  burette  132  c.  c.  of 
water,  and  allow  it  to  run  into  the  flask.  Shake  the  water  about  in 
the  flask  and  pour  into  the  bottle,  pour  a  part  of  the  contents  of  the 
bottle  into  the  flask  and  return  it  again  to  the  bottle,  to  insure  a 
uniform  mixing  of  all  the  water  with  the  acid. 

Calculations  may  be  still  further  shortened  by  using  for  each 
determination  such  quantities  of  the  substance  to  be  analyzed  that 
each  c.  c.  of  the  standard  solution  shall  correspond  to  1  per  cent,  of 
the  constituent  determined.  It  is  only  necessary  to  observe  the 
following  rule :  Take  of  the  substance  to  be  analyzed  a  weight  equal 
to  the  weight  of  the  constituent  to  be  determined  which  corre- 
sponds to  100  c.  c.  of  the  standard  solution. 

Suppose,  for  instance,  it  is  desired  to  determine  the  percentage 
of  H2SO4  in  several  samples  of  sulphuric  acid  which  may  be  concen- 
trated or  more  or  less  dilute  by  means  of  a  standard  alkali  solution, 
of  which 

1  c.  c.  =  0-014:2  grm.  H2SO4 
or 

100  c.  c.  =  1-1420  grm.  H2SO4 

If  now  1*1420  grm.  of  a  sample  be  accurately  weighed  off,  and  it  is 
found  that  100  c.  c.  of  the  alkali  solution  are  required  to  neutralize 
it,  the  sample  must  be  pure  H2SO4,  or  contain  100  per  cent,  of 
H2SO4.  If  1-1420  grm.  of  another  sample  requires  for  neutralization 
40  c.  c.  of  the  standard  alkali,  it  is  clear  that  it  contains  40  per  cent, 
of  H2SO4,  and,  finally,  that  the  percentage  will  equal  the  number 
of  c.  c.  used,  whatever  the  number  may  be.  This  mode  of  pro- 
ceeding is  of  course  applicable  in  the  determination  of  alkalies 
by  means  of  standard  acid  solutions,  or  in  determination  of  ele- 


§  192.]  ACIDIMETRY.  687 

ments  which  form  a  part  of  the  neutralized  body  ;  e.g.,  nitrogen  in 
ammonia. 

AYhen  the  substance  analyzed  contains  above  50  per  cent,  of 
the  constituent  to  be  determined,  it  is  preferable,  in  order  to  avoid 
using  too  large  a  quantity  of  standard  solution,  to  weigh  off  just 
half  the  quantity  required  by  the  preceding  rule  ;  then  each  c.  c.  of 
the  standard  solution  will  indicate  two  per  cent.,  or  the  percentage 
is  found  by  doubling  the  number  of  c.  c.  used.  On  the  other  hand, 
it  is  sometimes  advantageous  to  use  twice  or  perhaps  five  times  the 
quantity  demanded  by  the  first  rule,  in  which  case  the  percentage 
is  found  by  dividing  the  number  of  c.  c.  by  2  or  5. 

Often  when  the  substance  to  be  analyzed  is  in  solution,  or  solu- 
ble, it  is  advisable  to  weigh  five  times  the  amount  required,  dilute 
in  a  half-litre  flask  to  500  c.  c.  and  take  out  %  by  means  of  a  100 
c.  c.  pipette  for  the  determination. 

#.    Use  of  normal  solutions. 

Solutions  may  be  made  of  such  strength  that  1000  c.  c.  contain 
an  amount  of  acid  or  base  equivalent  to  1  gramme  of  hydrogen  ; 
one  molecule  of  an  acid  or  base  being  equivalent  to  the  number  of 
H  atoms  corresponding  to  the  quantivalence  of  its  radical.  Such 
solutions  are  called  normal  solutions. 

The  following  examples  show  the  relation  of  molecular  weights 
and  quantivalence  to  the  actual  weights  of  acids  and  bases  (or  salts) 
in  normal  solutions  :  — 


Mol.  .eight  Kadical. 

HC1  ........       36-46  Cl  1  36-46  grms. 

H2SO4  .......       98-  SO,  2  49-          « 

XH4OH  .....       35-  :NH4  1  35-          " 

XaOH  ......       40-04  ISTa  1  40-04      « 

(Xa.00,  .....     106-08  Na,  2  53-04      «  ) 


From  this  relation  it  follows  that  a  given  volume  of  any  nor- 
mal acid  solution  exactly  neutralizes  an  equal  volume  of  any  normal 
alkali  solution.  Moreover,  the  weight  of  any  acid  or  alkali  which 
1  c.  c.  of  a  normal  solution  neutralizes  can  be  very  easily  calculated. 

The  method  generally  used  for  preparing  normal  solutions  is 
to  first  make  solutions  of  acid  and  alkali  somewhat  stronger  than 
required,  ascertain  their  volumetric  relation  and  actual  strength,  as 


688  SPECIAL   PART.  [§  192. 

in  a,  page  680  ;  and  next  dilute  to  the  volume  required  to  make 
the  solutions  normal  by  addition  of  the  calculated  and  accurately 
measured  volume  of  water  as  described  above  under  y.  The 
trouble  involved  in  these  operations  overbalances  the  advantages 
of  normal  solutions  except  for  some  special  purposes.  By  using 
sodium  carbonate,  however,  for  the  alkali,  normal  solutions  may 
be  prepared  in  a  comparatively  simple  manner,  since  sodium  car- 
bonate, unlike  the  caustic  alkalies,  can  easily  be  procured  pure,  and 
can  be  accurately  weighed.  53 '08  grm.  of  pure  Na2CO3  previously 
ignited  to  dull  redness  are  dissolved  in  water  and  the  solution  is 
diluted  to  exactly  1000  c.  c.  To  make  a  normal  acid  solution  mix 
60  grm.  concentrated  sulphuric  acid  with  1050  c.  c.  water,  let  cool, 
and  ascertain  how  many  c.  c.  of  this  acid  neutralize  50  c.  c.  of  the 
normal  sodium  carbonate  solution. 

Suppose  48  •  6  c.  c.  acid  sol.  =  50  c.  c.  alkali  sol.; 

50 

then  1       "          «       = =  1.0288"-  " 

48-6 

or  1000       "          "       =  1028-8         "  « 

Accordingly  28  •  8  c.c.  of  water  must  be-  added  to  1000  c.  c.  of  the 
acid  solution  to  make  it  normal.  The  acid  solution  and  water  are 
measured  and  mixed  as  described  above  under  y.  Test  finally  the 
acid  against  the  alkali  to  be  certain  that  equal  volumes  neutralize 
each  other.  In  neutralization  it  is  not  necessary  to  expel  carbonic 
acid  by  boiling.  Tincture  of  cochineal  must  be  used  as  an  indica- 
tor. Litmus  is  quite  unsuitable,  since  in  the  presence  of  carbonic 
acid  the  change  of  color  which  it  undergoes  during  neutralization 
is  gradual  and  indistinct.  Even  cochineal  is  not  quite  indifferent 
to  carbonic  acid,  the  slight  excess  of  acid  or  alkali  required  to  pro- 
duce a  distinct  change  of  color  being  perceptibly  increased  by  its 
presence. 

The  error  thus  caused  by  the  .disturbing  influence  of  carbonic 
acid,  which  is  slight  when  normal  solutions  are  used,  is  increased 
when  more  dilute  standard  solutions  of  acid  and  alkali  are  used,  for 
the  more  dilute  the  solution  is,  the  greater  the  volume  required  to 
supply  the  slight  unavoidable  excess  of  acid  or  alkali.  A  standard 
solution  of  caustic  alkali  is  therefore  to  be  recommended  for  nicer 
investigation,  and  for  all  purposes  when  dilute  standard  solutions- 
-are  required. 

The  common  mineral  acids  in  a  free  state,  in  not  too  dilute  solu- 


§  193.]  ACIBIMETRY.  689 

tions  may  be  determined  with  sufficient  accuracy  for  many  techni- 
cal purposes  without  the  use  of  a  standard  acid  solution,  by  simply 
adding  tincture  of  cochineal  solution  to  a  suitable  weighed  amount 
previously  diluted  to  about  150  c.  c.,  and  neutralizing  cold  with  the 
normal  sodium  carbonate  solution. 


MODIFICATION  OF  THE  COMMON  ACIDIMETKIC   METHOD  (KIEFER*). 

§193. 

Instead  of  estimating  free  acid  by  a  solution  of  soda  of  known 
strength,  and  determining  the  neutralization  point  by  means  of 
cochineal  tincture,  an  ammoniacal  solution  of  copper  may  be  used 
for  the  purpose,  in  which  case  the  neutralization  point  is  known  by 
the  turbidity  observed  as  soon  as  the  free  acid  present  is  completely 
neutralized.  The  copper  solution  is  prepared  by  adding  to  an  aque- 
ous solution  of  cupric  sulphate,  solution  of  ammonia  until  the  pre- 
cipitate of  basic  salt  which  forms  at  first  is  just  redissolved.  After 
determining  the  strength  of  the  solution  by  standard  sulphuric  or 
hydrochloric  acid  (not  oxalic),  it  may  be  employed  for  the  estima- 
tion of  all  the  stronger  acids  (with  the  exception  of  oxalic  acid), 
provided  the  fluids  are  clear.  The  basic  cupric  salt,  in  the  precipi- 
tation of  which  the  final  reaction  consists,  is  not  insoluble  in  the 
ammonium  salt  formed,  and  its  solubility  depends  on  the  degree  of 
concentration,  and  on  the  presence  of  other  salts,  especially  of 
ammonium  salts  (CAKEY  LEA*)*).  Hence  the  method  cannot  boast 
of  scientific  accuracy,  but  as  the  variations  occasioned  by  the  causes 
mentioned  are  inconsiderable,  J  the  process  retains  its  applicability 
to  technical  purposes,  for  which,  indeed,  it  was  originally  proposed. 
This  method  is  of  especial  value  in  cases  in  which  free  acid  is  to  be 
determined  in  presence  of  a  normal  metallic  salt  with  acid  reaction ; 
-e.g.,  free  sulphuric  acid  in  mother-liquors  of  cupric .  sulphate  or 
zinc  sulphate,  &c.  It  is  advisable  to  determine  the  strength  of  the 
ammoniacal  copper  solution  anew  before  every  fresh  series  of 
experiments. 

*  Annal.  d.  Chem.  u.  Pharm.  93,  386. 
f  Chem.  News,  4,  195. 

\  Compare  my  experiments  on  the  subject  in  the  Zeitschrift  f .  analyt.  Chem. 
1,  108. 


690 


SPECIAL   PART. 


[§  193. 


TABLE  I. 

Percentages   of  Anhydrous   Potassa    (K2O)    corresponding   to   different   specific 
gravities  of  solution  of  potassa. 


Dalton. 

Tiinnermann  (at  15°). 

Specific 
gravity. 

Percentage 
of  anhydrous 
potassa. 

Specific 
gravity. 

Percentage 
of  anhydrous 
potassa. 

Specific 
gravity. 

Percentage 
of  anhydroua 
potassa. 

1-60 

46-7 

1-3300 

28  '290 

1-1437 

14-145 

•52 

42-9 

1-3131 

27-158 

1-1308             13-013 

•47 

39-6 

1-2966 

26-027 

1-1182             11-882 

•44 

36-8 

1-2803 

24-895 

1-1059             10-750 

•42 

34-4 

1-2648 

23-764 

1-0938              9-619 

•39 

32-4 

1-2493 

22-632 

1-0819 

8-487 

1-36 

29-4 

1-2342 

21-500 

1-0703 

7-355 

1-33 

26-3 

1-2268 

20-935 

1-0589 

6-224 

1-28 

23-4 

1-2122 

19-803 

1-0478 

5-002 

1-23 

19-5 

1-1979 

18-671 

1-0369 

3  961 

1-19 

16-2 

1-1839 

17-540 

1-0260 

2-829 

1-15 

13-0 

1-1702 

16-408 

1-0153 

1-697 

1-11 

9-5 

1-1568 

15-277 

1-0050 

0-5658 

1-06 

4-7 

TABLE  II. 

Percentages  of  Anhydrous  Soda  (Na2O)  corresponding  to  different  specific  gramtie 

'of  solution  of  soda. 


Dalton. 

Tiinnermann  (at  15"). 

Specific 
gravity. 

Percentage 
of  anhy- 
drous soda. 

Specific 
gravity. 

Percentage 
of  anhy- 
drous soda. 

Specific 
gravity. 

Percentage 
of  anhy- 
drous soda. 

Specific 
gravity. 

Percentage 
of  anhy- 
drous soda. 

1-56 

41-2 

1-4285 

30-220 

1-2982 

20-550 

1-1528 

10-275 

1-50 

36-8 

1-4193 

29-616 

1-2912 

19-945 

1-1428 

9-670 

1-47 

34-0 

1-4101 

29-011 

1-2843 

19-341 

1-1330 

9-066 

1-44 

31-0 

1-4011 

28-407 

1-2775 

18-730 

1-1233 

8-462 

1-40 

29-0 

1-3923 

27-802 

1-2708 

18-132 

1-1137 

7-857 

1-36 

26-0 

1-3836 

27-200 

1-2642 

17-528 

1-1042 

7-253 

1-32 

23-0 

1-3751 

26-594 

1-2578 

16-923 

1-0948 

6-648 

1-29 

19-0 

1-3668 

25-989 

1-2515 

16-319     '  1-0855 

6-044 

1-23 

16-0 

1-3586 

25-385 

1-2453 

15-714     i  1-0764 

5-440 

1-18 

13-0 

1-3505 

24-780 

1-2392 

15-110       1-0675 

4-835 

1-12 

9-0 

•3426 

24-176 

1-2280 

14-506 

1-0587 

4-231 

1-06 

4.7 

•3349 

23-572 

1-2178 

13-901 

1-0500 

3-626 

•3273 

22-967 

1-2058 

13-297 

1-0414 

3-022 

•3198 

22-363 

1-1948 

12-692 

1-0330 

2-418 

•3143 

21-894 

1-1841 

12-088 

1-0246 

1-813 

•3125 

21-758 

1-1734 

11-484 

1-0163 

1-209 

1-3053 

21-154 

1-1630 

10-879 

1  0081 

0-604 

ALKALIMETRY. 


691 


TABLE  III. 

Percentages  of  Ammonia  (NH3,    corresponding   to  different  specific  gmmties  of 
solution  of  ammonia  at  16°  (J.  OTTO). 


Specific 
gravity. 

!    Percentage 
of  ammonia. 

Specific 
gravity. 

Percentage 
of  ammonia. 

Specific          Percentage 
gravity.         of  ammonia. 

0-9517              12-000 

0-9607 

9-625             0-9697             7  '250 

0-9521             11-875 

0-9612 

9-500             0-9702             7'125 

0-9526             11-750 

0-9616 

9-375             0-9707 

7-000 

0-9531 

11-625 

0-9621 

9-250             0-9711 

6-875 

0-9536 

11-500 

0-9626 

9-125             0-9716 

6-750 

0-9540 

11-375 

0-9631 

9-000 

0-9721 

6-625 

0-9545            11-250 

0-9636 

8-875            0-9726 

6-500 

0-9550             11-125 

0-9641 

8-750            0-9730 

6-375 

0-9555             11-000 

0-9645 

8-625             0-9735 

6-250 

0-9556             10-950             0-9650 

8-500             0-9740 

6-125 

0-9559             10-875             0-9654 

8-375             0-9745 

6-000 

0-9564            10-750 

0-9659 

8-250             0-9749 

5-875 

0-9569             10-625 

0-9664 

8-125             0-9754 

5-750 

0-9574             10-500 

0-9669 

8-000             0-9759 

5-625 

0-9578             10-375 

0-9673 

7-875             0-9764 

5-500 

0-9583 

10-250 

0-9678 

7-750 

0-9768 

5-375 

0-9588 

10-125 

0-9683 

7-625 

0-9773 

5-250 

0-9593 

10-000 

0-9688 

7-500 

0-9778 

5-125 

0-9597 

9-875 

0-9692 

7-375 

0-9783 

5-000 

0-9602 

9-750 

3.  ALKALIMETKY. 

A.  ESTIMATION  OF  POTASS  A,  SODA,  OK  AMMONIA,  FROM  THE  SPE- 
CIFIC GRAVITY  OF  THEIR  SOLUTIONS. 

§194. 

In  pure  or  nearly  pure  solutions  of  hydrated  soda  or  potassa,  or 
of  ammonia,  the  percentage  of  alkali  may  be  estimated  from  the 
specific  gravity  of  the  solution. 

B.  ESTIMATION  OF  THE  TOTAL  AMOUNT  OF  CARBONATED  AND 
CAUSTIC  ALKALI  LN  CRUDE  SODA  AND  IN  POTASHES. 

The  "  soda  ash  "  of  commerce  is  a  crude  sodium  carbonate — 
the  "  potashes"  and  "  pearlash  "  a  crude  potassium  carbonate.  The 
commercial  value  of  these  articles  depends  on  the  percentage  of 
alkali  carbonate  (or  caustic  alkali)  that  they  contain,  which  is  very 
variable. 


692  SPECIAL   PART.  [§  195. 

I.  YOLUMETKIC  METHODS. 

Method  of  DESCKOIZILLES  and  GAY-LTJSSAC,  slightly  modified. 

§195. 

The  principle  of  tliis  method  is  the  converse  of  that  on  which 
the  acidimetric  method  described  §  192  is  based,  i.e.,  if  we  know 
the  quantity  of  an  acid  of  known  strength  required  to  saturate  an 
unknown  quantity  of  caustic  potassa  or  soda,  or  of  potassium  car- 
bonate or  sodium  carbonate,  we  may  readily  calculate  from  this 
the  amount  of  alkali  present. 

For  technical  analyses  we  may  employ  normal  sulphuric  acid. 
For  the  method  of  preparing  and  using  it,  see  p.  687 — 8. 

For  the  analysis  we  may  conveniently  weigh  off  such  a  quan- 
tity of  the  substance  that  the  number  of  c.  c.  of  acid  required  to 
neutralize  it  shall  directly  express  its  percentage  of  the  alkali 
or  carbonate  sought. 

Since  100  c.  c.  of  the  normal  solution  contain  -fa  of  98  grm. 
H3SO4,  the  proper  quantities  of  the  sodium  and  potassium  com- 
pounds to  employ  are  -fa  of  the  weight  of  the  compound  required 
to  neutralize  98  grm.  H3SO4  viz. : 

Potassa,  K2O 4*713  grm. 

Potassium  hydroxide,  KOH 5-613  " 

Potassium  carbonate,  KaCO3 6'913  " 

Hydrogen  potassium  carbonate,  KHCO, 10*013  " 

Soda,  Na2O 3-104  « 

Sodium  hydroxide,  NaOH 4-004  " 

Sodium  carbonate  (dry),  NaaCO3 5-304  " 

Sodium  carbonate  crystallized,  Na2CO8*10  HaO 14-304  " 

Hydrogen  sodium  carbonate,  NaHCO3 8*404  " 

With  regard  to  the  examination  of  pearlash  by  this  method^ 
the  following  points  deserve  attention  : — 

The  various  sorts  of  potash  of  commerce  contain,  besides  -ootas- 
fiium  carbonate  (and  caustic  potassa) : 

a.  Normal  salts  (e.g.,  potassium  sulphate,  potassium  chloride). 

J.  Salts  with  alkaline  reaction  (e.g.,  potassium  silicate,  potas- 
sium phosphate). 


§  195.]  ALKALIMETRY.  693 

c.  Admixtures  insoluble  in  water,  more  especially  calcium 
carbonate,  phosphate,  and  silicate. 

The  salts  named  in  a  exercise  no  influence  upon  the  results, 
but  not  so  those  named  in  b  and  c.  Those  in  c  may  be  removed 
by  filtration ;  but  the  admixture  of  the  salts  named  in  b  constitutes 
an  irremediable  though  slight  source  of  error ;  that  is  to  say,  if  it 
is  desired  to  confine  the  determination  to  the  caustic  and  car- 
bonated alkali.  But  as  regards  the  estimation  of  the  value  of 
pearlash  for  many  purposes,  the  term  error  cannot  be  applied ;  as, 
for  instance,  in  the  preparation  of  caustic  potassa,  by  boiling  the 
solution  with  lime,  the  alkali  combined  with  silicic  acid  and  with 
phosphoric  acid  is  converted,  like  the  carbonate,  into  the  caustic 
state. 

If  you  are  not  satisfied  with  finding  the  percentage  of  available 
alkali,  but  desire  also  to  know  whether  the  remainder  consists 
simply  of  foreign  salts,  or  whether  water  is  also  present,  the 
determination  of  the  latter  substance  must  precede  the  alkalimetric 
examination.  The  same  remark  applies  also  to  soda. 

With  regard  to  the  examination  of  soda  by  this  method,  the 
following  points  deserve  attention  : — 

The  soda  of  commerce,  prepared  by  LEBLANC'S  method,  con- 
tains, besides  sodium  carbonate,  always,  or  at  least  generally, 
sodium  hydroxide,  sodium  sulphate,  sodium  chloride,  sodium 
silicate  and  aluminate,  and  not  seldom  also  sodium  sulphide, 
sodium  thiosulphate  and  sulphite.* 

The  three  last-named  substances  impe.de  the  process,  and  inter- 
fere more  or  less  with  the  accuracy  of  the  results.  Their  presence 
is  ascertained  in  the  following  way  : — 

a.  Mix  with   sulphuric  acid ;  a  smell   of   hydrogen   sulphide 
reveals  the  presence  of  sodium  sulphide,  with  which  sodium  thio- 
sulphate is  also  invariably  associated. 

b.  Color  dilute  sulphuric  acid  with  a  drop  of  solution  of  potas- 
sium permanganate  or  chromate,  and  add  some  of  the  soda  under 
examination,  but  not  sufficient  to  neutralize  the  acid.     If  the  solu- 
tion  retains   its   color,    this   proves   the  absence  of   both  sodium 
sulphite  and  thiosulphate  ;  but  if  the  fluid  loses  its  color,  or  turns 
green,  as  the  case  may  be,  one  of  these  salts  is  present. 

c.  Whether  the  reaction  described  in  b  proceeds  from  sodium 

*  Traces  of  sodium  cyanide  are  also  occasionally  found. 


694  SPECIAL   PART.  [§  196. 

sulphite  or  thiosulphate  is  ascertained  by  supersaturating  a  clear 
solution  of  the  sample  under  examination  with  hydrochloric  acid. 
If  the  solution,  after  the  lapse  of  some  time,  becomes  turbid, 
owing  to  the  separation  of  sulphur  (emitting  at  the  same  time  the 
odor  of  sulphurous  acid),  this  may  be  regarded  as  a  proof  of  the 
presence  of  sodium  thiosulphate  ;  however,  the  solution  may, 
besides  the  thiosulphate,  also  contain  sodium  sulphite.  "With 
respect  to  the  detection  of  sodium  sulphite  in  the  presence  of 
thiosulphate,  comp.  "  Qual.  Anal.,"  p.  204. 

The  defects  arising  from  the  presence  of  the  three  compounds 
in  question  may  be  remedied  in  a  measure,  by  igniting  the  weighed 
sample  of  the  soda  with  potassium  chlorate,  before  proceeding  to 
saturate  it.  This  operation  converts  the  sodium  sulphide,  thiosul- 
phate, and  sulphite  into  sodium  sulphate.  But  if  sodium  thiosul- 
phate is  present,  the  process  serves  to  introduce  another  source  of 
error,  as  that  salt,  upon  its  conversion  into  sulphate,  decomposes  a 
molecule  of  sodium  carbonate,  and  expels  the  carbonic  acid  of  the 
latter  [NaaS2O3  +  4O  (from  the  potassium  chlorate)  +  Na2CO3  = 


The  presence  of  sodium  silicate  and  of  sodium  aluminate  may 
be  generally  recognized  by  the  separation  of  a  precipitate  as  soon 
as  the  solution  is  saturated  with  acid.  If  you  intend  the  result  to 
express  the  quantity  of  carbonated  and  caustic  alkali  only,  the 
presence  of  these  two  bodies  becomes  a  slight  source  of  error  ;  but 
if  you  wish  to  estimate  the  value  of  the  soda  for  many  purposes, 
no  error  will  be  caused. 

Method  of  FR.  MOHR,  modified. 
§196. 

Instead  of  estimating  the  alkalies  in  the  direct  way  by  means 
of  an  acid  of  known  strength,  we  may  estimate  them  also,  as  pro- 
posed first  by  FR.  MOHR,*  by  supersaturating  with  standard  acid, 
expelling  the  carbonic  acid  by  boiling,  and  finally  by  determining 
by  standard  alkali  solution  the  excess  of  standard  acid  added. 

This  process  gives  very  good  results,  and  is  therefore  particu- 
larly suited  for  scientific  investigations.  It  requires  the  standard 
fluids  mentioned  in  §  192,  viz.,  a  standard  acid  and  standard  solu- 

*  Annal.  d.  Chem.  u.  Pharm.  86,  129. 


§  197.]  ALKALIMETRY.  695 

tion  of  potassium  or  sodium  hydroxide.  Each  of  these  fluids  is 
filled  into  a  MOHR'S  burette. 

The  process  is  as  follows : — 

Dissolve  the  alkali  in  water,  and  add  a  measured  quantity  of 
tincture  of  cochineal ;  run  in  now  as  much  of  the  standard  acid  as 
will  suffice  to  impart  an  orange  tint  to  the  fluid ;  then  boil,  and 
remove  the  last  traces  of  carbonic  acid,  by  boiling,  shaking,  blow- 
ing into  the  flask,  and  finally  sucking  out  the  air. 

Now  add  standard  solution  of  potash,  drop  by  drop,  until  the 
-color  just  appears  violet.  There  is  no  difficulty  in  determining  the 
-exact  point  at  which  the  reaction  is  completed. 

If  the  standard  solutions  of  potash  and  acid  are  of  correspond- 
ing strength,  the  number  of  c.  c.  used  of  the  potash  solution  is 
simply  deducted  from  the  number  of  c.  c.  used  of  the  acid.  The 
remainder  expresses  the  volume  of  the  acid  solution  neutralized  by 
the  alkali  in  the  examined  sample.  If  the  two  standard  fluids  are 
not  of  corresponding  strength,  the  excess  of  acid  added,  and  sub- 
sequently neutralized  by  the  potash  solution,  is  calculated  from  the 
known  relation  the  one  bears  to  the  other. 

For  the  method  of  calculating  the  weight  of  any  alkali  corre- 
sponding to  1  c.  c.  of  a  standard  solution  is  given  in  §  192,  p.  682. 

With  regard  to  certain  variations  from  the  ordinary  course 
which  are  occasionally  convenient,  comp.  p.  685. 

§  197. 

There  now  still  remain  two  questions  to  be  considered,  which 
are  of  importance  for  the  estimation  of  the  commercial  value 
of  potash  and  soda.  The  first  concerns  the  separate  determination 
of  the  caustic  alkali,  which  the  sample  under  examination  may 
contain  besides  the  carbonate;  the  second,  the  determination  of 
sodium  carbonate  in  presence  of  potassium  carbonate. 

The  product  may  be  tested  qualitatively  for  caustic  alkali  by 
adding  to  a  solution  barium  chloride  so  long  as  a  precipitate 
forms ;  if  the  solution  still  remains  alkaline,  presence  of  caustic 
alkali  is  indicated. 

C.  DETERMINATION  OF  THE  CAUSTIC  ALKALI  WHICH  COMMERCIAL 
ALKALI  MAY  CONTAIN  BESIDE  THE  CARBONATE. 

Many  kinds  of  potashes  and  crude  soda,  more  especially  the 
latter,  contain,  besides  alkali  carbonate,  also  caustic  alkali ;  and  the 


696  SPECIAL   PAfcT.  [§  197. 

chemist  is  often  called  upon  to  determine  the  amount  of  the  latter ; 
as  it  is,  for  instance,  by  no  means  a  matter  of  indifference  to  the 
soap-boiler  how  much  of  the  soda  is  supplied  to  him  already  in  the 
caustic  state.  This  may  be  effected  as  follows  : — 

a.  Determine  in   a  portion   of  the   substance    carbonic   acid 
directly:  convert  the  caustic  alkali  in   another  weighed   portion 
into  carbonate  by  mixing  with  about  an  equal  quantity  of  sand  and 
about  j-  its  weight  of  ammonium  carbonate,  adding  as  much  water 
as  the  mass  will  absorb,  evaporating  and  igniting  to  expel  water, 
and  determine  carbonic  acid   in   the   residue.     Deduct   the   per- 
centage of  carbonic  acid  found  in  the  original  substance  from  that 
found  after  treatment  with  ammonium  carbonate.    An  amount  of 
caustic  alkali  must  be  present  equivalent  to  this  difference  (for 
44:  pts.  CO2,  62-08  pts.  Na2O,  or  94-26  pts.  K2O). 

b.  Determine  (according  to  §  196)  the  total  amount  of  alkali 
existing  both  as  carbonate  and  caustic,  and  reckon  it  all  as  car- 
bonate.  In  another  portion  determine  the  caustic  alkali  as  follows : 
Dissolve  a  suitable  weighed  portion  in  a  measuring  flask,  add  barium 
chloride  so  long  as  a  precipitate  forms,  fill  to  the  mark  with  water, 
shake  and  allow  to  settle  clear  without  exposure  to  the  air,  take  out 
a  known  portion  of  the  supernatant  clear  fluid  with  a  pipette,  and 
determine  volumetrically  the  caustic  alkali  or  equivalent  barium 
hydroxide  which  it  contains.     The  amount  actually  existing  as  car- 
bonate can  now  be  found  by  calculating  the  carbonate  equivalent 
to  the  caustic  thus  found,  and  deducting  it  from  the  total  amount 
of  alkali  found  and  reckoned  as  carbonate  in  the  other  portion. 


D.  ESTIMATION  OF  SODIUM  CARBONATE  IN  PRESENCE  OF  POTAS- 
SIUM CARBONATE. 

Soda,  being  much  cheaper  than  potash,  is  occasionally  used  to 
adulterate  the  latter.  The  common  alkalimetric  methods  not  only 
fail  to  detect  this  adulteration,  but  they  give  the  admixed  sodium 
carbonate  as  potassium  carbonate.  Many  processes*  have  been 
proposed  for  estimating  in  a  simple  way  the  soda  contained  in 
potash,  but  not  one  of  them  can  be  said  to  satisfy  the  requirements 
of  the  case. 

The  following  tolerably  expeditious  process,  however,   gives 


*Comp.  Handworterbuch  der  Chemie,  2  Aufl.,  I.  443. 


§  198.]  ESTIMATION    OF   ALKALI-EARTH   METALS.  697 

accurate  results :  Dissolve  6*25  grm.  of  the  gently-ignited  pearlash 
in  water,  filter  the  solution  into  a  quarter-litre  flask,  add  acetic  acid 
in  slight  excess,  apply  a  gentle  heat  until  the  carbonic  acid  is 
expelled,  then  add  to  the  fluid,  while  still  hot,  lead  acetate,  drop  by 
drop,  until  the  formation  of  a  precipitate  of  lead  sulphate  just 
ceases ;  allow  the  mixture  to  cool,  add  water  up  to  the  mark, 
shake,  allow  to  deposit,  filter  through  a  dry  filter,  and  transfer 
200  c.  c.  of  the  filtrate,  corresponding  to  5  grin,  of  pearlash,  to  a 
J-litre  flask.  Add  hydrogen  sulphide  water  up  to  the  mark,  and 
shake.  If  the  lead  acetate  has  been  carefully  added,  the  fluid  will 
now  smell  of  hydrogen  sulphide,  and  no  longer  contain  lead ;  in 
the  contrary  case,  hydrogen  sulphide  gas  must  be  conducted  into 
it.  After  the  lead  sulphide  has  subsided,  filter  through  a  dry 
filter.  Evaporate  50  c.  c.  of  the  filtrate  (corresponding  to  1  grm.  of 
pearlash)  with  addition  of  10  c.  c.  hydrochloric  acid,  of  1*10  sp.  gr., 
in  a  weighed  platinum  dish,  to  dryness,  then  cover  the  dish,  heat, 
and  weigh ;  the  weight  found  expresses  the  total  quantity  of  po- 
tassium and  sodium  chlorides  given  by  1  grin,  of  the  pearlash. 
Estimate  the  potassium  and  sodium  now  severally  in  the  indirect 
way,  by  determining  the  chlorine  volumetrically  (§  141,  I.,  b).  For 
the  calculation  of  the  results,  see  "  Calculation  of  Analyses"  in  the 
Appendix. 

4.  ESTIMATION  OF  ALKALI-EAKTH  METALS  BY  THE 
ALKALIMETKIC  METHOD. 

§198. 

The  alkali-earth  metals,  when  in  the  form  of  oxides,  hydrox- 
ides, or  carbonates,  may  also  be  determined  volumetrically  by  means 
of  standard  acid  and  alkali  solutions.  Standard  sulphuric  acid  may 
be  used  for  magnesium  ;  standard  nitric  acid  for  barium,  strontium, 
and  calcium.  The  only  advantage  which  these  acids  possess  over 
hydrochloric  is  that  there  is  less  liability  of  loss  on  heating  solu- 
tions containing  them  in  the  free  state,  which  is  necessary  when  car- 
bonic is  present.  Hydrochloric  acid  can,  however,  be  used  with  safety 
if  precaution  be  taken  to  avoid  the  presence  of  an  unnecessary 
quantity  when  the  solution  is  heated. 

If  an  oxide  or  hydroxide  free  from  carbonic  acid  is  to  be  exam- 
ined, add  some  water  to  a  weighed  quantity,  and  allow  the  standard 
acid  to  flow  in  from  a  burette  until  solution  is  effected  and  the  solu- 


698  SPECIAL   PAST.  [§  199. 

tion  colored  with  litmus  or  cochineal  gives  an  acid  reaction.  Then 
determine  the  excess  of  acid  used  by  means  of  the  standard  alkali 
solution. 

In  case  of  a  carbonate,  dissolve  in  a  flask,  adding  first  water, 
then  standard  hydrochloric  acid  from  a  burette  in  small  successive 
portions,  until  solution  is  complete ;  next  add  the  indicator  (litmus 
or  cochineal)  and  allow  the  standard  alkali  solution  to  run  in  from 
a  burette  until  the  free  acid  is  nearly  neutralized.  Now  remove 
the  carbonic  acid  by  boiling  a  few  minutes,  and  complete  the  neu- 
tralization with  the  standard  alkali. 

To  calculate  the  amount  of  the  alkali-earth  metal,  deduct  from 
the  volume  of  standard  acid  used  the  amount  neutralized  by  the 
total  quantity  of  standard  alkali  used  (which  is  calculated  from  the 
known  volumetric  relation  of  the  two  solutions) ;  the  remainder  has 
formed  a  normal  salt  with  the  alkali-earth  metal.  The  quantity 
found  to  be  required,  its  absolute  strength,  molecular  weight,  and 
the  atomic  weight  of  the  alkali-earth  metal,  are  data  for  calculating 
the  amount  of  the  latter,  in  the  manner  explained  on  pp.  681-4.  If 
hydrochloric  acid  is  used  for  a  standard  acid,  bear  in  mind  that  2 
mol.  correspond  to  1  at.  of  an  alkali-earth  metal. 

5.  CHLOEIMETEY. 
§199. 

The  "chloride  of  lime,"  or  bleaching  powder"  of  commerce, 
contains  calcium  hypochlorite,  calcium  chloride,  and  calcium 
hydroxide.  The  two  latter  ingredients  are  for  the  most  part  com- 
bined with  one  another  as  calcium  oxychloride.  In  freshly  pre- 
pared and  perfectly  normal  chloride  of  lime,  the  quantities  of  cal- 
cium hypochlorite  and  calcium  chloride  present  stand  to  each  other 
in  the  proportion  of  their  mol.  weights.  "When  such  chloride  of  lime 
is  brought  into  contact  with  dilute  sulphuric  acid,  the  whole  of  the 
chlorine  it  contains  is  liberated  in  the  elementary  form,  in  accord- 
ance with  the  following  equation  :— 

CaCLA  +  CaCl,  +  2H2SO4  =  2CaSO4  +  2  H2O  +  401. 

On  keeping  chloride  of  lime,  however,  the  proportion  between  cal- 
cium hypochlorite  and  calcium  chloride  gradually  changes — the 
former  decreases,  the  latter  increases.  Hence,  from  this  cause  alone, 
to  say  nothing  of  original  difference,  the  commercial  article  is  not 


§  200.]  CHLOUIMETKY.  699 

of  uniform  quality,  and  on  treatment  with  acid  gives  sometimes 
more  and  sometimes  less  chlorine. 

As  the  value  of  this  article  depends  entirely  upon  the  amount 
of  chlorine  set  free  on  treatment  with  acid,  chemists  have  devised 
various  simple  methods  of  determining  the  available  amount  of 
chlorine  in  any  given  sample.  These  methods  have  collectively 
received  the  name  of  Chlorimetry.  We  describe  a  few  of  the  best. 

PREPARATION  OF  THE  SOLUTION  OF  CHLORIDE  OF  LIME. 

The  solution  is  prepared  alike  for  all  methods,  and  best  in  the 
following  manner : — 

Weigh  off  10  grm.,  triturate  finely  with  a  little  water,  add  grad- 
ually more  water,  pour  the  liquid  into  a  litre  flask,  triturate  the 
residue  again  with  water,  and  rinse  the  contents  of  the  mortar  care- 
fully into  the  flask ;  fill  the  latter  to  the  mark,  shake  the  milky 
fluid,  and  examine  it  at  once  in  that  state,  i.e.,  without  allowing  it 
to  deposit ;  and  every  time,  before  measuring  off  a  fresh  portion, 
shake  again.  The  results  obtained  with  this  turbid  solution  are 
much  more  constant  and  correct  than  when,  as  is  usually  recom- 
mended, the  fluid  is  allowed  to  deposit,  and  the  experiment  is  made 
with  the  supernatant  clear  portion  alone.  The  truth  of  this  may> 
readily  be  proved  by  making  two  separate  experiments,  one  with 
the  decanted  clear  fluid,  and  the  other  with  the  residuary  turbid 
mixture.  Thus,  for  instance,  in  an  experiment  made  in  my  own 
laboratory,  the  decanted  clear  fluid  gave  22*6  of  chlorine,  the  residu- 
ary mixture  25'0,  the  uniformly  mixed  turbid  solution  24'5. 

1  c.  c.  of  the  solution  of  chloride  of  lime  so  prepared  corre- 
sponds to  O'Ol  grm.  chloride  of  lime. 

A.  PENOT'S  Method.* 
§  200. 

This  method  is  based  upon  the  conversion  of  arsenious  acid  into 
arsenic  acid,  or  more  strictly,  an  arsenite  into  an  arsenate,  since  the 
conversion  is  effected  in  an  alkaline  solution.  Potassium  iodide- 
starch  paper  is  employed  to  ascertain  the  exact  point  when  the  reac- 
tion is  completed. 

*  Bulletin  de  la  Societe  Industrielle  de  Mulhouse,  1852,  No.  118.— Dingler's 
Polytech.  Journal,  127,  134. 


700  SPECIAL  PAKT.  [§  200. 

a.  Preparation  of  the  Potassium  Iodide-Starch  Paper. 

The  following  method  is  preferable  to  the  original  one  given  by 
PENOT  : — 

Stir  3  grm.  of  potato  starch  in  250  c.  c.  of  cold  water,  boil  with 
stirring,  add  a  solution  of  1  grm.  potassium  iodide  and  1  grin, 
crystallized  sodium  carbonate,  and  dilute  to  500  c.  c.  Moisten  strips 
of  fine  white  unsized  paper  with  this  fluid,  and  dry. '  Keep  in  a 
closed  bottle. 

1).  Preparation  of  the  solution  of  Arsenious  Acid. 

Dissolve  4-436  grrn.  of  pure  arsenious  oxide  (As2O3)  and  13  grm, 
pure  crystallized  sodium  carbonate  in  600 — 700  c.  c.  water,  with  the 
aid  of  heat,  let  the  solution  cool,  and  then  dilute  to  1  liter.  Each  c.  c. 
of  this  solution  contains  an  amount  of  sodium  arsenite  equivalent 
to  0-004436  grm.  arsenious  oxide  (As3O3),  which  corresponds  to  1 
c.  c.  chlorine  gas  of  0°  and  760  mm.  atmospheric  pressure.* 

As  sodium  arsenite  in  alkaline  solution  is  liable,  when  exposed 
to  access  of  air,  to  be  gradually  converted  into  sodium  arsenate, 
PENOT' s  solution  should  be  kept  in  small  bottles  with  glass  stoppers, 
filled  to  the  top,  and  a  fresh  bottle  used  for  every  new  series  of 
experiments.  According  to  Fr.  MoHKf  the  solution  keeps 
unchanged,  if  the  arsenious  oxide  and  the  sodium  carbonate  are 
both  absolutely  free  from  oxidizable  matters  (arsenious  sulphide,, 
sodium  sulphide,  and  sodium  sulphite). 

*  Penot  gives  the  quantity  of  arsenious  oxide  as  4'44;  but  I  have  corrected 
this  number  to  4'436,  in  accordance  with  the  now  received  atomic  weights  of  the 
substances  and  specific  gravity  of  chlorine  gas — after  the  following  propor- 
tion : — 

141-84  (4  at.  01):  198  (1.  mol.  As2O8) ::  317763  (weight  of  1  litre  of  chlorine  gas):?/ 
x  =  4 '436,  i.e.,  the  quantity  of  arsenious  oxide  which  1  litre  of  chlorine  gas 
converts  into  arsenic  acid. 

This  solution  is  arranged  to  suit  the  foreign  method  of  designating  the 
strength  of  chloride  of  lime — viz.,  in  chlorimetrical  degrees  (each  degree  repre- 
sents 1  litre  chlorine  gas  at  0°  and  760  mm.  pressure  in  a  kilogramme  of  the  sub- 
stance). This  method  was  proposed  by  Gay-Lussac.  The  degrees  may  readily 
be  converted  into  per  cents,  and  vice  'versa,  thus:  A  sample  of  chloride  of  lime 
of  90°  contains  90  X  317763  =  285'986  grm.  chlorine  in  1000  grm.  or  28*59  in 
100;  and  a  sample  containing  34'2  per  cent,  chlorine  is  of  107 '6°,  for  100  grm.  of 
the  substance  contain  34'2  grm.  chlorine;  .  • .  1000  grm.  of  the  substance  contain 
342  grm.  chlorine,  but  342  grm.  chlorine  =  -S-TTT^  litres  =  107'6  litres;  .  • .  1000 
grm.  of  the  substance  contain  107'6  litres  chlorine. 

f  His  Lehrbuch  der  Titrirmethode,  2  Aufl.,  S.  290. 


§  201.]  CHLORIMETRY.  701 

c.  The  Process. 

Measure  off,  with  a  pipette,  50  c.  c.  of  the  solution  of  chloride  of 
lime  prepared  according  to  the  directions  of  §  199,  transfer  to  a 
beaker,  and  from  a  50  c.  c.  burette  add  slowly,  and  at  last  drop  by 
drop,  the  solution  of  arsenious  acid,  with  constant  stirring,  until  a 
drop  of  the  mixture  produces  no  longer  a  blue-colored  spot  on  the 
iodized  paper  ;  it  is  very  easy  to  hit  the  point  exactly,  as  the  grad- 
ually increasing  faintness  of  the  blue  spots  made  on  the  paper  by 
the  fluid  dropped  on  it  indicates  the  approaching  termination  of  the 
reaction,  and  warns  the  operator  to  confine  the  further  addition  of 
the  solution  of  arsenious  acid  to  a  single  drop  at  a  time.  The  num- 
ber of  £  c.  c.  used  indicates  directly  the  number  .of  chlorirnetrical 
degrees  (see  note),  as  the  following  calculation  shows :  Suppose  you 
have  used  40  c.  c.  of  solution  of  arsenious  acid,  then  the  quantity  of 
chloride  of  lime  used  in  the  experiment  contains  40  c.  c.  of  chlorine 
gas.  Now,  the  50  c.  c.  of  solution  employed  correspond  to  0*5  grm. 
of  chloride  of  lime ;  therfore  0'5  grm.  of  chloride  of  lime  contain 
40  c.  c.  chlorine  gas,  therefore  1000  grm.  contain  80000  c.  c.  =  80 
litres^  This  method  gives  very  constant  and  accurate  results,  and 
appears  to  be  particularly  well  suited  for  use  in  manufacturing 
establishments  where  there  is  no  objection,  on  the  score  of  danger, 
to  the  employment  of  arsenious  acid.  (Expt.  No.  99.) 

B.  OTTO'S  Method. 
§  201. 

The  principle  of  this  method  is  as  follows  :— 

Two  molecules  of  ferrous  sulphate  when  brought  in  contact 
with  chlorine  in  presence  of  water  and  free  sulphuric  acid,  give  1 
mol.  ferric  sulphate  and  2  mol.  HC1,  the  process  consuming  2  at. 
chlorine. 

2FeS04  +  H2S04  +  2C1  =  Fe(SO4)3  +  2HC1. 
1  mol.  crystallized  ferrous  sulphate  : — 

(FeS04-7H30)  =  278 

correspond  to  35'46  of  chlorine,  or,  in  other  terms,  0'7839  grm. 
crystallized  ferrous  sulphate  correspond  to  0*1  grm.  chlorine. 

The  ferrous  sulphate  required  for  these  experiments  is  best  pre- 
pared as  follows : — 


702  SPECIAL    PART.  [§  201. 

Take  iron  nails,  free  from  rust,  and  dissolve  in  dilute  sulphuric 
acid,  applying  heat  in  the  last  stage  of  the  operation  :  filter  the  solu- 
tion, still  hot,  into  about  twice  its  volume  of  common  alcohol.  The 

precipitate  consists  of 

7HaO. 


Collect  upon  a  filter,  wash  with  common  alcohol,  spread  upon  a 
sheet  of  blotting  paper,  and  dry  in  the  air.  When  the  mass  smells 
no  longer  of  alcohol,  transfer  to  a  bottle  and  keep  this  well  corked. 
Instead  of  ferrous  sulphate,  ammonium  ferrous  sulphate  (p.  118) 
may  be  used.  0*1  grin,  of  chlorine  reacts  with  1-1055  grm.  of  this 
double  sulphate. 

The  Process. 

Dissolve  3-1356  grm.  (4  X  '7839  grm.)  of  the  precipitated  fer- 
rous sulphate,  or  4-422  grm.  (4  X  1'1055  grm.)  of  ammonium  fer- 
rous sulphate,  with  addition  of  a  few  drops  of  dilute  sulphuric 
acid,  in  water,  to  200  c.  c.  ;  take  out,  with  a  pipette,  50  c.  c.,  corre- 
sponding to  0*7839  grm.  ferrous  sulphate,  or  1-1055  grm.  ammonium 
ferrous  sulphate,  dilute  with  150  —  200  c.  c.  water,  add  a  sufficiency 
of  pure  hydrochloric  acid,  and  run  in  from  a  50  c.  c.  burette  the 
freshly  shaken  solution  of  chloride  of  lime,  prepared  according  to 
§  199,  until  the  ferrous  sulphate  is  completely  converted  into  ferric 
sulphate.  To  know  the  exact  point  when  the  reaction  is  completed, 
place  a  number  of  drops  of  a  solution  of  potassium  ferricyanide  on 
a  plate,  and  when  the  operation  is  drawing  to  an  end  apply  some 
of  the  mixture  with  a  stirring-rod  to  one  of  the  drops  on  the  plate, 
and  observe  whether  it  produces  a  blue  precipitate  ;  repeat  the 
experiment  after  every  fresh  addition  of  two  drops  of  the  solution 
of  chloride  of  lime.  When  the  mixture  no  longer  produces  a  blue 
precipitate  in  the  solution  of  potassium  ferricyanide  on  the  plate, 
read  off  the  number  of  volumes  used  of  the  solution  of  chloride  of 
lime. 

The  amount  of  solution  of  chloride  of  lime  used  contained  O'l 
grm.  of  chlorine.  Suppose  40  c.  c.  have  been  used  :  as  every  c.  c. 
corresponds  to  0*10  grm.  of  chloride  of  lime,  the  percentage  by 
weight  of  available  chlorine  in  the  chloride  of  lime  is  found  by  the 
following  proportion  :  — 

0-40  :  0-10  ::  100  :»;  #  =  25; 

or,  by  dividing  1000  by  the  number  of  c.  c.  used  of  the  solution  of 
chloride  of  lime. 


§  201.]  CHLORIMETRY.  703 

This  method  also  gives  very  satisfactory  results,  provided 
always  that  the  ferrous  salt  is  perfectly  dry  and  free  from  ferric 

salt. 

Modification  of  the  preceding  Method. 

Instead  of  the  solution  of  ferrous  sulphate,  a  solution  of  ferrous 
chloride,  prepared  by  dissolving  pianoforte  wire  in  hydrochloric 
acid  (according  to  p.  268),  may  be  used  with  the  best  results.  If 
0-6316  of  pure  metallic  iron,  i.  e.,  0'6335  of  fine  pianoforte  wire 
(which  may  be  assumed  to  contain  99'7  per  cent,  of  iron),  are  dis- 
solved to  200  c.  c.,  the  solution  so  prepared  contains  exactly  the 
same  amount  of  iron  as  the  solution  of  ferrous  sulphate  above  men- 
tioned— that  is  to  say,  50  c.  c.  of  it  correspond  to  0*1  gnu.  chlorine. 
But  as  it  is  inconvenient  to  weigh  off  a  definite  quantity  of  iron 
wire,  the  following  course  may  be  pursued  in  preference  :  Weigh  off 
accurately  about  0'15  grin.,  dissolve,  dilute  the  solution  to  about 
200  c.  c.,  convert  the  ferrous  into  ferric  chloride  with  the  solution 
of  chloride  of  lime,  prepared  according  to  the  directions  of  §  199, 
and  calculate  the  chlorine  by  the  proportion 

56  :  35*46  ::  the  quantity  of  iron  used  :  x\ 

the  x  found  corresponds  to  the  chlorine  contained  in  the  amount 
used  of  the  solution  of  chloride  of  lime.  This  calculation  may  be 
dispensed  with  by  the  application  of  the  following  formula,  in 
which  the  carbon  in  the  pianoforte  wire  is  taken  into  account : — 

Multiply  the  weight  of  the  pianoforte  wire  by  6313,  and  divide 
the  product  by  the  number  of  c.  c  used  of  the  solution  of  chloride 
of  lime;  the  result  expresses  the  percentage  of  chlorine  by 
weight. 

This  method  gives  very  good  results.  I  have  described  it  here 
principally  because  it  dispenses  altogether  with  the  use  of  standard 
fluids.  It  is  therefore  particularly  well  adapted  for  occasional 
examinations  of  samples  of  chloride  of  lime,  and  also  by  way  of 
control.  (See  Expt.  No.  99.) 

C.  BTJNSEN'S  Method. 

Pour  10  c.  c.  of  the  solution  of  chloride  of  lime,  prepared  accord- 
ing to  the  directions  of  §  199  (containing  O'l  chloride  of  lime),  into 
a  beaker,  and  add  about  6  c.  c.  of  the  solution  of  potassium  iodide, 
prepared  according  to  p.  445  (containing  0'6  KI)  ;  dilute  the  mix- 


704  SPECIAL   PAKT.  [§  202. 

ture  with  about  100  c.  c.  of  water,  acidify  with  hydrochloric  acid, 
and  determine  the  liberated  iodine  as  directed  §  146.  As  1  at. 
iodine  corresponds  to  1  at.  chlorine,  the  calculation  is  easy.  This 
method  gives  excellent  results.  (Compare  Expt.  No  99.) 

6.  EXAMINATION  OF  BLACK  OXIDE  OF  MANGANESE. 

§  202. 

The  native  black  oxide  of  manganese  (as  also  the  regenerated 
artificial  product)  is  a  mixture  of  manganese  dioxide  with  lower 
oxides  of  that  metal,  and  with  ferric  oxide,  clay,  &c., ;  it  also  inva- 
riably contains  moisture,  and  frequently  chemically  combined 
water.  The  commercial  value  of  the  article  depends  entirely  upon 
the  amount  of  dioxide  (or,  more  correctly  expressed,  of  available 
oxygen)  which  it  contains.  By  "  available  oxygen  "  we  understand 
the  excess  of  oxygen  contained  in  a  manganese,  over  the  1  at.  com- 
bined with  the  metal  to  monoxide ;  upon  treating  the  ore  with 
hydrochloric  acid,  an  amount  of  chlorine  is  obtained  equivalent  to 
this  excess  of  oxygen.  This  available  oxygen  is  always  expressed 
in  the  form  of  manganese  dioxide.  1  at.  corresponds  to  1  mol.  man- 
ganese dioxide,  since  MnO2  =  MnO  -|-  O. 

I.  DRYING  THE  SAMPLE. 

All  analyses  of  manganese  proceed,  of  course,  upon  the  suppo- 
sition that  the  sample  operated  upon  is  a  fair  average  specimen  of 
the  ore.  A  portion  of  a  tolerably  finely  powdered  average  sample 
is  generally  sent  for  analysis  to  the  chemist ;  in  the  case  of  new 
lodes,  however,  a  number  of  samples,  taken  from  different  parts  of 
the  mine,  are  also  occasionally  sent.  If,  in  the  latter  case,  the  aver- 
age composition  of  the  ore  is  to  be  ascertained,  and  not  simply  that 
of  several  samples,  the  following  course  must  be  resorted  to  :  Crush 
the  several  samples  of  the  ore,  in  an  iron  mortar,  to  coarse  powder, 
and  pass  the  whole  of  this  through  a  rather  coarse  sieve.  Mix  uni- 
formly, then  remove  a  sufficiently  large  portion  of  the  coarse  pow- 
der with  a  spoon,  reduce  it  to  powder  in  a  steel  mortar,  passing  the 
whole  of  this  through  a  fine  sieve.  Mix  the  powder  obtained  by 
this  second  process  of  pulverization  most  intimately ;  take  about  8 
— 10  grm.  of  it,  and  triturate  this,  in  small  portions  at  a  time,  in 
an  agate  mortar,  to  an  impalpable  powder.  Average  samples  are 


§303."]  EXAMINATION    OF    MANGANESE.  705 

generally  already  sufficiently  tine  to  require  only  the   last  opera- 


» 
tion. 


As  regards  the  temperature  at  which  the  powder  is  to  be 
dried,  if  you  desire  to  expel  the  whole  of  the  moisture  without  dis- 
turbing any  of  the  water  of  hydration,  the  temperature  adopted 
must  be  120°  (this  is  the  result  of  my  own  experiments,  see  Expt. 
?s  o.  100).  But,  as  there  appears  to  be  at  present  an  almost  univer- 
sal understanding,  in  the  manganese  trade,  to  limit  the  drying  tem- 
perature to  100°,  the  fine  powder  is  exposed,  in  a  shallow  copper  or 
brass  pan,  for  6  hours,  to  the  temperature  of  boiling  water,  in  a 
water  bath  (p.  53,  fig.  23.) 

When  the  samples  have  been  dried,  they  are  introduced,  still 
hot,  into  glass  tubes  12 — 14  cm.  long  and  8 — 10  mm.  wide,  sealed 
at  one  end  ;  these  tubes  are  then  corked  and  allowed  to  cool. 

In  laboratories  where  whole  series  of  analyses  of  different  ores 
are  of  frequent  occurrence,  it  is  advisable  to  number  the  drying- 
pans  and  glass  tubes,  and  to  transfer  the  samples  always  from  the 
pan  to  the  tube  of  the  corresponding  number. 

II.  DETERMINATION  OF  THE  MANGANESE  DIOXIDE. 
§  203. 

Of  the  many  methods  that  have  been  proposed  for  the  valuation 
of  manganese  ores,  I  select  three  as  the  most  expeditious  and  accu- 
rate. The  first  is  more  particularly  adapted  for  technical  pur- 
poses. 

A.  FRESENIFS  and  WILL'S  Method. 

a.  If  oxalic  acid  (or  an  oxalate)  is  brought  into  contact  with 
manganese  dioxide  in  presence  of  water  and  excess  of  sulphuric 
acid,  manganous  sulphate  is  formed,  and  carbon  dioxide  evolved, 
while  the  oxygen,  which  we  may  assume  to  exist  in  the  manganese 
dioxide  in  combination  with  the  monoxide,  combines  with  the  ele- 
ments of  the  oxalic  acid,  and  thus  converts  the  latter  into  carbon 
dioxide. 

Mn02  +  H2S04  +  H2C204  =  MnSO4  -f  2H2O  +  2CO2. 

Each  atom  of  available  oxygen,  or,  what  amounts  to  the  same, 
each  mol.  binoxide  of  manganese  =  87.  gives  2  mol.  carbon  dioxide 

=  88. 


706  SPECIAL   PAKT.  [§  203. 

b.  If  this  process  is  performed  in  a  weighed  apparatus  from 
which  nothing  except  the  evolved  carbonic  acid  can  escape,  and 
which,  at  the  same  time,  permits  the  complete  expulsion  of  that 
acid,  the  diminution  of  weight  will  at  once  show  the  amount  of 
carbonic  acid  which  has  escaped,  and  consequently,  by  a  very  sim- 
ple calculation,  the  quantity  of  dioxide  contained  in  the  analyzed 
manganese  ore.     As  88  parts,  by  weight,  of  carbon  dioxide  corre- 
spond to  87  of  manganese  dioxide,  the  carbon  dioxide  found  need 
simply  be  multiplied  by  87,  and  the  product  divided  by  88,  or  the 
carbon  dioxide  may  be  multiplied  by 

§?_0-9887, 

88~~ 

to  find  the  corresponding  amount  of  manganese  dioxide. 

c.  But  even  this  calculation  may  be  avoided  by  simply  using  in 
the  operation  the  exact  weight  of  ore  which,  if  the  latter  con- 
sisted of  pure  dioxide,  would  give  100  parts  of  carbon  dioxide. 

The  number  of  parts  evolved  of  carbon  dioxide  expresses,  in 
that  case,  directly  the  number  of  parts  of  dioxide  contained 
in  100  parts  of  the  analyzed  ore.  It  results  from  J  that  98-87 
is  the  number  required.  Suppose  the  experiment '  is  made 
with  0*9887  grm.  of  the  ore,  the  number  of  centigrammes  of 
carbon  dioxide  evolved  in  the  process  expresses  directly  the 
percentage  of  dioxide  contained  in  the  analyzed  manganese  ore. 
Now,  as  the  amount  of  carbon  dioxide  evolved  from  0-9887 
grm.  of  manganese  would  be  rather  small  for  accurate  weigh- 
ing, it  is  advisable  to  take  a  multiple  of  this  weight,  and  to 
divide  afterwards  the  number  of  centigrammes  of  carbon  dioxide 
evolved  from  this  multiple  weight  by  the  same  number  by  which 
the  unit  has  been  multiplied.  The  multiple  which  answers  the  pur- 
pose best  for  superior  ores  is  the  triple,  =  2'966  ;  for  inferior  ores, 
I  recommend  the  quadruple,  —  3-955,  or  the  quintuple,  =  4-9435, 

The  analytical  process  is  performed  in  the  apparatus  illustrated 
in  fig.  58,  p.  409. 

The  flask  A  should  hold,  up  to  the  neck,  about  120  c.  c. ;  B 
about  100  c.  c.  The  latter  is  half  filled  with  sulphuric  acid ;  the 
tube  a  is  closed  at  l>  with  a  little  wax  ball,  or  a  very  small  piece  of 
caoutchouc  tubing,  with  a  short  piece  of  glass  rod  inserted  in  the 
other  end. 

Place  2-966,  or  3-955,  or  4-9435  grm.— according  to  the  quality 


§  203.  J  EXAMINATION   OF   MANGANESE.  707 

of  the  ore — in  a  watch-glass,  and  tare  the  latter  most  accurately  on 
a  delicate  balance ;  then  remove  the  weights  from  the  watch-glass, 
and  replace  them  by  manganese  from  the  tube,  very  cautiously, 
with  the  aid  of  a  gentle  tap  with  the  linger,  until  the  equilibrium  is 
exactly  restored.  Transfer  the  weighed  sample,  with  the  aid  of  a 
card,  to  the  flask  ^1,  add  5 — 6  gnn.  normal  sodium  oxalate,  or 
about  7'5  grm.  normal  potassium  oxalate,  in  powder,  and  as  much 
water  as  will  fill  the  flask  to  about  one  third.  Insert  the  cork  iuto 
A,  and  tare  the  apparatus  on  a  strong  but  delicate  balance,  by 
means  of  shot,  and  lastly,  tinfoil,  not  placed  directly  on  the  scale, 
but  in  an  appropriate  vessel.  The  tare  is  kept  under  a  glass  bell. 
Try  whether  the  apparatus  closes  air-tight.  Then  make  some  sul- 
phuric acid  flow  from  B  into  A,  by  applying  suction  to  d,  by 
means  of  a  caoutchouc  tube.  The  evolution  of  carbon  dioxide  com- 
mences immediately  in  a  steady  and  uniform  manner.  When  it 
begins  to  slacken,  cause  a  fresh  portion  of  sulphuric  acid  to  pass 
into  A,  and  repeat  this  until  the  manganese  ore  is  completely 
decomposed,  which,  if  the  sample  has  been  very  finely  pulverized, 
requires  at  the  most  about  five  minutes.  The  complete  decompo- 
sition of  the  analyzed  ore  is  indicated,  on  the  one  hand,  by  the  ces- 
sation of  the  disengagement  of  carbon  dioxide,  and  its  non-renewal 
upon  the  influx  of  a  fresh  portion  of  sulphuric  acid  into  A  ;  and,  on 
the  other  hand,  by  the  total  disappearance  of  every  trace  of  black 
powder  from  the  bottom  of  A.* 

Xow  cause  some  more  sulphuric  acid  to  pass  from  B  into  A, 
to  heat  the  fluid  in  the  latter,  and  expel  the  last  traces  of  carbon 
dioxide  therein  dissolved  ;  remove  the  wax  stopper,  or  india-rubber 
tube,  from  i,  and  apply  gentle  suction  to  d  until  the  air  drawn  out 
tastes  no  longer  of  carbon  dioxide.  Let  the  apparatus  cool  com- 
pletely in  the  air,  and  place  it  on  the  balance,  with  the  tare  on  the 
other  scale,  and  restore  equilibrium.  The  number  of  centigramme 
weights  added,  divided  by  3,  4,  or  5,  according  to  the  multiple  of 
0:9887  grm.  used,  expresses  the  percentage  of  dioxide  contained  in 
the  analyzed  ore. 

In  experiments  made  with  definite  quantities  of  the  ore,  weigh- 
ing in  an  open  watch-glass  cannot  well  be  avoided,  and  the  dried 
manganese  is  thus  exposed  to  the  chance  of  a  reabsorption  of  water 


*  If  the  manganese  ore  has  been  pulverized  in  an  iron  niortar,  a  few  black 
spots  (particles  of  iron  from  the  mortar)  will  often  remain  perceptible. 


708  SPECIAL  :PAKT.  L 

from  the  air,  which  of  course  tends  to  interfere,  to  however  so 
trifling  an  extent,  with  the  accuracy  of  the  results.  In  very  pre- 
cise experiments,  therefore,  the  best  way  is  to  analyze  an  indeter- 
minate quantity  of  the  ore,  and  to  calculate  the  percentage  as 
shown  above.  For  this  purpose,  one  of  the  little  corked  tubes, 
filled  with  the  dry  pulverized  ore,  is  accurately  weighed,  and 
about  3  to  5  grm.  (according  to  the  quality  of  the  ore)  are  trans- 
ferred to  the  flask  A.  By  now  re  weighing  the  tube,  the  exact 
quantity  of  ore  in  the  flask  is  ascertained.  To  facilitate  this  opera- 
tion, it  is  advisable  to  scratch  on  the  tube,  with  a  iile,  marks  indi- 
cating approximately  the  various  quantities  which  may  be  required 
for  the  analysis,  according  to  the  quality  of  the  ore. 

With  proper  skill  and  patience  on  the  part  of  the  operator,  a 
good  balance  and  correct  weights,  this  method  gives  most  accurate 
and  corresponding  results,  differing  in  two  analyses  of  the  same 
ore  barely  to  the  extent  of  (>2  per  cent. 

If  the  results  of  two  assays  differed  by  more  than  0*2  per  cent., 
a  third  experiment  should  be  made.  In  laboratories  where  analyses 
of  manganese  ores  are  matters  of  frequent  occurrence,  it  will  be 
found  convenient  to  use  an  aspirator  for  sucking  out  the  carbon 
dioxide.  In  the  case  of  very  moist  air,  the  error  which  proceeds 
from  the  fact  that  the  water  in  the  air  drawn  through  the  appara- 
tus is  retained,  and  which  is  usually  quite  inconsiderable,  may  now 
be  increased  to  an  important  extent.  Under  such  circumstances, 
connect  the  end  of  the  tube  b  with  a  calcium  chloride  tube  during 
the  suction. 

Very  accurate  determinations  may  also  be  made  by  weighing 
the  evolved  carbon  dioxide.  For  this  purpose  the  apparatus 
described  on  page  414,  fig.  61,  is  well  adapted.  From  '5  to  1.  grin, 
ore  should  be  used  for  a  determination.  Introduce  the  ore  and 
oxalic  acid  or  oxalate  into  the  decomposing  flask,  fill  the  flask  about 
one  third  with  water,  connect  the  several  parts  of  the  apparatus  as 
for  the  determination  of  carbonic  acid,  decompose  the  ore  by 
admitting  gradually  strong  sulphuric  acid,  remove  the  evolved  CO2 
completely  from  the  unweighed  portion  of  the  apparatus  into  the 
potash  bulbs  as  described  for  the  determination  of  CO3. 

Some  ores  of  manganese  contain  carbonate*  of  the  alkali-earth 
i net < ilx,  which  of  course  necessitates  a  modification  of  the  foregoing 
process.  To  ascertain  whether  carbonates  of  the  alkali-earth  metals 
are  present,  boil  a  sample  of  the  pulverized  ore  with  water,  and 


g  203.]  EXAMINATION    OF    MANUANKSK.  709 

add  nitric  acid.  If  any  effervescence  takes  place,  the  process  is 
modified  as  follows  (RottR?): 

After  the  weighed  portion  of  ore  has  been  introduced  into 
the  liask  ^4,  treat  it  with  water,  so  that  the  flask  may  be  about 
i  full,  add  a  few  drops  of  dilute  sulphuric  acid  (1  part,  by  weight, 
sulphuric  acid,  to  5  parts  water)  and  warm  with  agitation,  prefer- 
ably in  a  water  bath.  After  some  time  dip  a  rod  in  and  test 
whether  the  fluid  possesses  a  strongly  acid  reaction.  If  it  does 
not,  add  more  sulphuric  acid.  As  soon  as  the  whole  of  the  car- 
bonates are  decomposed  by  continued  heating  of  the  acidified  fluid, 
completely  neutralize  the  excess  of  acid  with  soda  solution  free 
from  carbonic  acid,  allow  to  cool,  add  the  usual  quantity  of  sodium 
oxalate,  and  proceed  as  above. 

If  you  have  no  soda  solution  free  from  carbonic  acid  at  hand, 
you  may  place  the  sodium  oxalate  or  oxalic  acid  (about  3  grin.)  in 
a  small  tube,  and  suspend  this  in  the  flask  A  by  means  of  a  thread 
fastened  by  the  cork.  When  the  apparatus  is  tared,  and  you  have 
>atisfied  yourself  that  it  is  air-tight,  release  the  thread  and  proceed 
as  above. 

B.  BUNSEN'S  Method. 

Reduce  the  ore  to  the  very  finest  powder,  weigh  off  about  0*4 
grm.,  introduce  this  into  the  small  flask  #,  illustrated  in  fig.  64,  p. 
435,  and  pour  pure  fuming  hydrochloric  acid  over  it ;  conduct  the 
process  exactly  as  in  the  analysis  of  chromates.  Boil  until  the  ore 
is  completely  dissolved  and  all  the  chlorine  expelled,  which  is 
effected  in  a  few  minutes.  2  atoms  of  iodine  separated  coriespond 
to  2  at.  chlorine  evolved,  and  accordingly  to  1  mol.  of  manganese 
dioxide.  For  the  estimation  of  the  separated  iodine,  the  method 
£  140  may  be  employed.  Results  most  accurate. 

C.  Estimation  of  tJi<?  Mwnganese  Dto.ride  l>y  wean*  of-I-run. 

Dissolve,  in  a  small  long- necked  flask,  placed  in  a  slanting  posi- 
tion, about  1  grm.  pianoforte  wire,  accurately  weighed,  in  moder- 
ately concentrated  pure  hydrochloric  acid  ;  weigh  off  about  0'6  grm. 
of  the  sample  of  manganese  ore  in  a  little  tube,  drop  this  into  the 
flask,  with  its  contents,  and  heat  cautiously  until  the  ore  is  dis- 
solved. 1  mol.  of  manganese  dioxide  converts  2  at.  of  dissolved 
iron  from  the  state  of  ferrous  to  ferric  chloride.  When  complete 

*  Zeitschr.  f.  anal.  Them.  1,  48. 


710  SPECIAL   PART.  [g  - 

solution  lias  taken  place,  dilute  the  contents  of  the  flask  with  water, 
allow  to  cool,  rinse  into  a  beaker,  and  determine  the  iron  still 
remaining  in  the  state  of  ferrous  chloride  with  potassium  dichro- 
mate  (p.  274).  Deduct  this  from  the  weight  of  the  wire  employed 
in  the  process ;  the  difference  expresses  the  quantity  of  iron  which 
has  been  converted  by  the  oxygen  of  the  manganese  from  ferrous 
to  ferric  chloride.*  This  difference  multiplied  by  4|^5-  or  0-7768 
gives  the  amount  of  manganese  dioxide  in  the  analyzed  ore.  This 
method  also,  if  carefully  executed,  gives  very  accurate  results. 

The  main  reason  why  this  method  is  less  suitable  for  industrial 
use  than  the  first  lies  in  the  fact  that  the  analyst  must  work  with 
much  smaller  quantities  of  substance.  Hence  to  obtain  results 
equally  accurate  with  those  yielded  by  A,  far  greater  nicety  in 
weighing  and  manipulating  is  required.  Instead  of  metallic  iron, 
weighed  quantities  of  pure  ferrous  sulphate  or  ferrous  ammonium, 
sulphate  may  be  used. 


III.  ESTIMATION  OF  MOISTURE  IN  MANGANESE, 
§  204. 

In  the  purchase  and  sale  of  manganese,  a  certain  proportion  of 
moisture  is  usually  assumed  to  be  present,  and  often  a  percentage 
is  fixed  within  which  the  moisture  must  be  confined.  In  estimat- 
ing the  moisture  the  same  temperature  should  be  employed,  at 
which  the  drying  for  the  purpose  of  determining  the  dioxide  is 
effected  (§  202,  I.). 

As  the  amount  of  moisture  in  an  ore  may  be  altered  by  the 
operations  of  crushing  and  pulverizing,  the  experiment  should  be 
made  with  a  sample  of  the  mineral  which  has  not  yet  been  sub- 
jected to  these  processes.  The  drying  must  be  continued  until  no 
further  diminution  of  weight  is  observed  ;  at  100°,  this  takes  about 
6  hours ;  at  1 20°,  generally  only  1 J  hours.  If  the  moisture  in  a 
manganese  ore  is  not  to  be  estimated  on  the  spot,  but  in  the  labora- 
tory, a  fair  average  sample  of  the  ore  should  be  forwarded  to  the 
chemist  in  a  strong,  perfectly  dry,  and  well-corked  bottle. 


*  In  very  precise  experiments,  the  weight  of  the  iron  must  be  multiplied  by 
0-997,  since  pianoforte  wire  ma}-  always  be  assumed  to  contain  about  0'003 
impurities. 


§  206.]  ANALYSIS   OF   COMMON   SALT.  711 

IV.  ESTIMATION  OF  THE  AMOUNT  OF  HYDROCHLORIC  Acn>  REQUIRED 

FOR    THK    COMPLETE    DECOMPOSITION    OF    A    MANGANESE. 

§205. 

Different  manganese  ores,  containing  the  same  amount  of  avail- 
able oxygen,  or,  as  it  is  usually  expressed,  of  binoxide  of  manga- 
nese, may  require  very  different  quantities  of  hydrochloric  acid  to 
effect  their  decomposition  and  solution,  so  as  to  give  an  amount  of 
-chlorine  corresponding  to  the  available  oxygen  in  them ;  thus,  an 
•ore  consisting  of  60  per  cent,  of  binoxide  of  manganese  and  40  per 
•cent,  of  sand  and  clay  requires  4  mol.  hydrochloric  acid  to  1  at.  of 
available  oxygen;  whereas  an  equally  rich  ore  containing  lower 
oxides  of  manganese,  ferric  oxide,  or  calcium  carbonate  requires  a 
jnuch  larger  proportion  of  hydrochloric  acid. 

The  quantity  of  hydrochloric  acid  in  question  may  be  deter- 
in  ined  by  the  following  process : — 

Determine  volumetrically  the  strength  of  a  moderately  strong 
hydrochloric  acid  (of,  say,  1*10  sp.  gr.).  Warm  10  c.  c.  of  the  same 
acid  with  a  weighed  quantity  (about  1  grm.)  of  the  manganese,  in 
a,  small,  long-necked  flask,  with  a  glass  tube,  about  3  feet  long, 
fitted  into  the  neck.  Fix  the  flask  in  a  position  that  the  tube  is 
directed  obliquely  upwards,  and  then  gently  heat  the  contents. 
As  soon  as  the  manganese  is  decomposed,  apply  a  somewhat 
.stronger  heat  for  a  short  time,  to  expel  the  chlorine  which  still 
remains  in  solution  ;  but  carefully  avoid  continuing  the  application 
•of  heat  longer  than  is  absolutely  necessary,  as  it  is  of  importance 
to  guard  against  the  slightest  loss  of  hydrochloric  acid.  Let  the 
flask  cool,  dilute  the  contents  with  water,  and  determine  the  free 
hydrochloric  acid  remaining.  Deduct  the  quantity  found  from 
that  originally  added  ;  the  difference  expresses  the  amount  of 
hydrochloric  acid  required  to  effect  the  decomposition  of  the  man- 


1.  ANALYSIS   OF  COMMON  SALT. 

§206. 

I  select  this  example  to  show  how  to  analyze,  with  accuracy  and 
tolerable  expedition,  salts  which,  with  a  predominant  principal 
ingredient,  contain  small  quantities  of  other  substances. 


712  SPECIAL   PART.  [§  206. 

a.  Keduce  the  salt  by  trituration  to  a  uniform  powder,  and  put 
this  into  a  stoppered  bottle. 

b.  Weigh  off  10  grm.  of  the  powder,  and  dissolve  in  a  beaker 
by  digestion  with  water ;  filter  the  solution  into  a  -J-litre  flask,  and 
thoroughly    wash    the    small    residue    which    generally    remains. 
Finally,  fill  the  flask  with  water  up  to  the  mark,  and  shake  the 
fluid. 

If  small  white  grains  of  calcium  sulphate  are  left  on  dissolving 
the  salt,  reduce  them  to  powder  in  a  mortar,  add  water,  let  the 
mixture  digest  for  some  time,  decant  the  clear  supernatant  fluid 
on  to  a  filter,  triturate  the  undissolved  deposit  again,  add  water, 
&c.,  and  repeat  the  operation  until  complete  solution  is  effected. 

c.  Ignite  and  weigh  the  dried  insoluble  residue  of  b,  and  subject 
it  to  a  qualitative  examination,  more  especially  with  a  view  to  ascer- 
tain whether  it  is  perfectly  free  from  calcium  sulphate. 

(L  Of  the  solution  5,  measure  off  successively  the  following 
quantities : 

For  e.    50  c.  c.  corresponding  to  1  grm.  of  common  salt. 

"  /.  150  c.  c.  «  "    3          «  « 

«    g.  150  c.  c.  "  "3  "  " 

"    h.    50  c.c.  «  «    I          "  " 

e.  Determine  in  the  50  c.  c.  measured  off,  the  chlorine  as  directed 
§  141,  L,  a  or  I. 

f.  Determine  in  the  150  c.  c.  measured  off,  sulphuric  acid  as 
directed  §  132,  L,  1. 

g.  Determine  in  the  150  c.  c.  measured  off,  the  calcium  and 
magnesium,  as  directed  p.  496,  28. 

h.  Mix  the  50  c.  c.  measured  off  in  a  platinum  dish,  with  about 
\  c.  c.  of  pure  concentrated  sulphuric  acid,  and  proceed  as  directed 
£  98,  1. .  The  neutral  residue  contains  the  sulphates  of  sodiumr 
calcium,  and  magnesium.  Deduct  from  this  the  quantity  of  the 
two  latter  substances  as  resulting  from  g ;  the  remainder  is  sodium. 
sulphate. 

i.  Determine  in  another  weighed  portion  of  the  salt,  the  water 
as  directed  §  35,  a,  a,  at  the  end. 

k.  Bromine  and  other  bodies,  of  which  only  very  minute  traces 
are  found  in  common  salt,  are  determined  by  the  methods  described 
in  Part  I. 


§207.]  ANALYSIS   OF -GUNPOWDER.  713 

8.  ANALYSIS   OF   GUNPOWDER* 

§207. 

Gunpowder,  as  is  well  known,  consists  of  nitre,  sulphur,  and  char- 
coal, and,  in  the  ordinary  condition,  invariably  contains  a  small  quan- 
tity of  moisture.  The  analysis  is  frequently  confined  to  the  deter- 
mination of  the  three  constituents  and  the  moisture,  but  often  the 
examination  is  extended  to  the  nature  of  the  charcoal,  and  the  car- 
bon, hydrogen,  oxygen,  and  ash  therein  are  estimated. 

<(.  Determination  of  the  Moixtnre. 

Weigh  2 — 3  grm.  of  the  substance  (not  reduced  to  powder) 
between  two  well-fitting  watch-glasses,  and  dry  in  the  desiccator,  or 
at  a  gentle  heat,  not  exceeding  60°,  till  the  weight  remains  con- 
stant. 

l>.  Determination  of  the  Nitre. 

Place  an  accurately  weighed  quantity  (about  5  grm.)  on  a  filter, 
moistened  with  water ;  saturate  with  water,  and,  after  some  time, 
repeatedly  pour  small  quantities  of  hot  water  upon  it  until  the 
potassium  nitrate  is  completely  extracted.  Receive  the  first  filtrate 
in  a  small  weighed  platinum  dish,  the  washings  in  a  beaker  or 
small  flask.  Evaporate  the  contents  of  the  platinum  dish  cau- 
tiously, adding  the  washings  from  time  to  time,  heat  the  residue 
cautiously  to  incipient  fusion,  and  weigh  it.f 

c.  Determination  of  the  Sulphur. 

Oxidize  2 — 3  grm.  of  the  powder  with  pure  concentrated  nitric 
acid  and  potassium  chlorate,  the  latter  being  added  in  small  por- 
tions, while  the  fluid  is  maintained  in  gentle  ebullition.  If  the 
operation  is  continued  long  enough,  it  usually  happens  that  both 
the  charcoal  and  sulphur  are  fully  oxidized,  and  a  clear  solution  is 


*  As  regards  the  determination  of  the  sp.  gr.  of  gunpowder,  I  refer  to  HEER- 
EN'S  paper  on  the  subject,  in  Mittheilungen  des  Gewerbevereins  fur  Hannover, 
1856,  198—178;  Polyt.  Centralbl.  1856,  1118. 

f  The  potassium  nitrate  may  also  be  estimated  in  an  expeditious  manner,  and 
with  sufficient  accuracy  for  technical  purposes,  by  means  of  a  hydrometer,  which 
is  constructed  to  indicate  the  percentage  of  this  ingredient  when  floated  in  water 
containing  a  certain  proportion  of  gunpowder  in  solution.  A  method  based 
upon  the  same  principle,  proposed  by  Uchatius,  is  given  in  the  Wiener  akad.  Ber. 
X.  748:  also  Anna!,  d.  ('hem.  u.  Pharm.  88,  395. 


714  SPECIAL    PAKT.  [§  208. 

finally  obtained.  Evaporate  with  excess  of  pure  hydrochloric  acid 
on  a  water-bath  to  dryness,  filter,  if  undissolved  charcoal  should 
render  it  necessary,  and  determine  the  sulphuric  acid  after  §  132, 

i,  i. 

d.  Determination  of  the  Charcoal. 

Digest  a  weighed  portion  of  the  powder  repeatedly  with 
.ammonium  sulphide,  till  all  sulphur  is  dissolved,  collect  the  char- 
coal on  a  filter  dried  at  100°,  wash  it  first  with  water  containing 
ammonium  sulphide,  then  with  pure  water,  dry  at  100°,  and  weigh. 

The  charcoal  so  obtained  must,  under  all  circumstances,  be 
tested  for  sulphur  by  the  method  given  under  <?,  and  if  occasion 
require,  the  sulphur  must  be  determined  in  an  aliquot  part.  The 
charcoal  may  also  be  examined  as  regards  its  behavior  to  potash 
solution  (in  which  u  red  charcoal"  *  is  partially  soluble)  and  an 
aliquot  part  may  be  subjected  to  elementary  analysis  according  to 
§  ITT  or  §  ITS.  For  this  latter  purpose  take  a  portion  of  the  char- 
coal dried  at  100°,  and  dry  at  190°  (WELTZIEN).  If  the  charcoal, 
on  this  second  drying,  suffers  a  diminution  of  weight,  calculate  the 
latter  into  per  cents,  of  the  gunpowder,  deduct  it  from  the  charcoal, 
and  add  it  to  the  moisture. 

U.  ANALYSIS  OF  SILICATES  AND  SILICEOUS  BOOKS. 

§208. 

The  separation  of  silica  in  silicates  which  are  decomposable  by 
acids  has  been  described  in  §  140,  II.,  a. ;  and  in  silicates  which 
are  not  thus  decomposed  in  §  140,  II.,  ~b.  For  determination  of  the 
alkalies,  see  page  426,  y.  Methods  for  separating  the  other  basic 
metals  more  commonly  occurring  in  silicates  are  given  in  §  161. 
Some  silicates  contain  water,  fluorine,  and  iron  both  in  the  ferrous 
and  ferric  state,  while  siliceous  rocks  may  contain  in  addition  small 
quantities  of  carbonic  acid,  titanic  acid,  sulphur,  phosphoric  acid, 
&c.,  due  to  admixture  of  various  minerals. 

Below  are  some  remarks  respecting  processes  which  may  be 
required  in  such  cases,  more  especially  in  the  analysis  of  rocks. 

1.  Decomposition.  If  the  greater  part  of  the  rock  mass  is 
undecomposable  by  acids,  fuse  directly  with  sodium  carbonate,  and 

*  Incompletely  carbonized  wood. 


§  208.]  ANALYSIS   OF   SILICATES.  715 

separate  silica  according  to  §  140,  II.,  I.  If  the  greater  part  Ls 
decomposable  by  hydrochloric  acid,  treat  with  hydrochloric  acid 
and  evaporate  to  dryness  as  described  in  §  140,  II.,  a,  for  separation 
<>f  silica.  Treat  the  residue  with  strong  hydrochloric  acid  5  to  lo 
minutes,  add  water  and  filter.  The  insoluble  portion,  consisting 
of  silica  and  the  undecomposed  part  of  the  rock,  is  ignited  with  the 
filter  in  a  platinum  crucible  and  fused  with  sodium  carbonate. 
Silica  is  then  separated  in  the  usual  manner,  and  the  second  solution 
of  basic  metals  thus  obtained  is  added  to  the  first.  Alkalies  are 
determined  in  another  portion  by  the  method  of  J.  L.  Smith 
(page  426.) 

2.  Water.  Silicates  dried  at  100°  occasionally  contain  wut^r. 
This  is  determined  by  taking  a  weighed  portion  dried  at  100°  and 
igniting  in  a  platinum  crucible,  or — in  presence  of  carbon,  carbon- 
ates, or  ferrous  iron — in  a  tube,  through  which  a  stream  of  dry  air 
is  drawn,  the  moisture  expelled  from  the  substance  being  retained 
by  a  weighed  calcium  chloride  tube. 

If  the  escaping  aqueous  vapors  manifest  acid  reaction,  owing 
TO  disengagement  of  hydrofluoric  acid  or  silicon  fluoride,  mix  the 
substance  with  6  parts  of  finely  triturated  recently  ignited  lead 
oxide  in  a  small  retort,  weigh,  ignite,  and  weigh  again.  This 
method,  however,  cannot  be  used  if  carbonic  acid  as  well  as  fluor- 
rine  is  present.  In  that  case  the  method  employed  by  L.  SIPOCZ* 
may  be  used.  Ignite  4  parts  sodium  carbonate  in  a  platinum  cru- 
cible till  water  is  completely  expelled,  allow  to  cool  to  50°  or  60°, 
mix  intimately  with  a  platinum  wire  with  1  part  of  the  pulverized 
dried  silicate,  introduce  the  mixture  into  a  capacious  platinum  boat, 
rinsing  out  the  last  adhering  portions  with  sodium  carbonate.  The 
boat,  provided  with  a  cover,  is  now  placed  in  the  middle  of  a  por- 
celain tube  (glazed  inside)  and  heated  in  an  air  bath  an  hour  to  120° 
or  130°  C.  During  this  time  every  trace  of  moisture  should  be 
removed  from  the  mixture  by  passing  dried  air  by  means  of  a  gaso- 
meter through  the  tube.  The  end  of  the  tube  through  which  the 
current  of  air  makes  its  exit  is  provided  with  a  calcium  chloride 
tube,  which  at  the  end  of  the  drying  process  is  replaced  by  a 
weighed  F  tube,  containing  glass  beads  moistened  with  pure  strong 
sulphuric  acid.  The  substance  is  now  brought  to  a  red  heat  in  a 
combustion  furnace,  and  a  regulated  current  of  air  (dried  by  sul- 


*Zeitschr.  f.  anal.  Chernie.  17,  207. 


716  SPECIAL   PART.  [§  208. 

plmric  acid)  is  passed  over  it  about  lialf  an  hour  to  carry  the  expelled 
water  vapor  into  the  absorbing  apparatus.  (It  is  obvious  that  this 
method  can  be  used  in  any  .case  instead  of  ignition  with  lead 
oxide). 

3.  Carbonic  acid  and  water.  If  it  can  be  proved  by  a  prelimi- 
nary experiment,  that  carbonic  acid,  as  well  as  water,  can  be  com- 
pletely removed  by  intense  ignition,  and  no  other  constituents 
(ferrous  iron,  manganese,  fluorine,  sulphides,  alkali  fluorides,  and 
chlorides,  &c.)  are  present  which  will  cause  change  of  weight  on 
ignition;  the  joint  amount  of  water  and  carbonic  acid  may  be 
determined  by  loss  of  weight  on  ignition,  and  carbonic  acid  in 
another  portion  according  to  §  139,  II.,  e.  The  amount  of  water 
present  equals  the  difference  between  the  two  quantities  thus 
found.  If,  as  is  usually  the  case,  the  nature  of  the  substance  does 
not  allow  the  joint  amount  of  water  and  carbonic  acid  to  be  deter- 
mined by  loss  on  ignition,  water  may  be  determined  by  the  method 
recommended  by  SIPOCZ  (described  above  in  2).  A  much  simpler 
and  sufficiently  accurate  method,  however,  is  to  determine  both 
water  and  carbonic  acid  at  once  by  ignition  of  the  substance  with 
lead  chromate  mixed  with  y1^  its  weight  of  potassium  dichromate 
in  a  combustion  tube,  collecting  and  weighing  the  evolved  water 
and  carbonic  acid.  The  process  is  conducted  precisely  as  in  the 
combustion  of  organic  compounds  (see  §  177)  except  that  it  is  not 
necessary  (unless  sulphides  are  present)  to  place  lead  chromate  in 
front  of  the  mixture  of  chromates  with  the  pulverized  rock.  Heat 
should  be  applied  toward  the  end  of  the  process  sufficient  to  fuse 
the  mixture.  It  is  desirable  to  use  2  grm.  or  even  more  of  the  sub- 
stance for  the  determination,  and  to  take  great  care  to  avoid  pres- 
ence of  hygroscopic  moisture  in  the  chromates.  Carbonaceous 
matter  (rarely  present  in  rocks)  would  of  course  interfere  with  the 
determination  of  COa  by  this  process.* 

4.  Ferrous  iron  is  most  readily  determined  by  decomposing  with 
a  mixture  of  sulphuric  and  hydrofluoric  acids  and  titration  with 
potassium  permanganate  according  to§  160,  84,  page  526.  With  a 
little  skill  and  proper  attention,  the  simple  method  of  effecting  the 

*  Very  satisfactory  results  were  obtained  both  by  myself  and  Mr.  W.  <L 
Comstock  in  the  determination  of  CO2  in  Iceland  spar  by  this  method.  Mr. 
Com  stock  also  obtained  equally  accurate  results  where  a  considerable  quantity 
of  pulverized  fluor  spar  was  added  to  the  weighed  Iceland  spar,  showing  that 
presence  of  fluorides  does  not  interfere  with  the  process. — O.  D.  A. 


ANALYSIS    OF    SILICATES.  717 

decomposition  described  at  the  end  of  84  can  safely  be  employed, 
unless  the  substance  is  unusually  difficult  to  decompose. 

5.  Titanic  uc'id  is  frequently  present  in  siliceous  rocks  in  quan- 
tity sufficient  to  be  determined.  In  the  ordinary  process  of  analy- 
sis, a  part  of  it  remains  with  the  separated  and  weighed  silica,  while 
the  remainder  is  precipitated  and  weighed  along  with  the  ferric 
and  aluminium  oxides.  Both  portions  may  be  brought  together, 
and  determined  as  follows  :  Dissolve  the  silica  in  the  platinum  cru- 
cible in  which  it  has  been  weighed  with  hydrofluoric  acid,  adding 
also  a  few  drops  of  pure  dilute  sulphuric  acid,  and  evaporate  on  a 
water-bath  ;  add  to  the  residue  2  or  3  c.  c:  of  hydrofluoric  acid,  and 
evaporate  again  to  ensure  complete  removal  of  silica.  Ignite  the 
residue  strongly  and  weigh,  in  order  to  be  able  to  deduct  from  the 
weight  of  the  silica  the  amount  of  impurities  thus  found  in  it. 
Add  next  to  the  residue  a  little  sodium  carbonate  and  fuse.  After 
cooling,  add  strong  sulphuric  acid  drop  by  drop  till  with  the  aid  of 
heat  the  mas*  is  dissolved.  It  is  best  to  use  so  much  sulphuric 
acid  that  the  mass  will  just  remain  liquid  on  cooling.  It  will  then 
easily  dissolve  in  a  small  quantity  of  water.  Dissolve  it  in  water 
and  reserve  the  solution. 

Dissolve  the  weighed  ferric  and  aluminium  oxides  by  prolonged 
digestion  in  concentrated  hydrochloric  acid ;  12  to  24  hours  will 
usually  suffice  for  the  solution  if  the  oxides  have  not  been  too 
strongly  ignited.  Some  flocks  of  silica,  however,  and  possibly 
titanic  acid  may  remain  In  order  to  ensure  solution  of  the  latter, 
add  2(>  c.  c.  dilute  sulphuric  acid  and  evaporate  till  fumes  of  sul- 
phuric acid  appear ;  cool,  add  a  little  water,  digest  till  sulphates, 
Arc.,  are  dissolved,  filter  off  and  weigh  the  traces  of  silica,  add  the 
filtrate  to  the  solution  of  titanic  acid  previously  obtained.  Add 
next  to  the  solution,  sodium  carbonate  until  a  slight  precipi- 
tate is  formed  which  does  not  redissolve  on.  stirring.  Xext  add  4 
c.  c.  pure  dilute  sulphuric  acid,  which  is  designed  to  dissolve  the 
slight  precipitate  and  prevent  precipitation  of  iron  along  with  tita- 
nium in  the  subsequent  part  of  the  process  (too  much  free  acid 
would  prevent  complete  precipitation  of  the  titanic  acid).  Solu- 
tion of  sulphurous  acid  is  then  added  to  reduce  the  iron  to  ferrous 
sulphate,  the  solution  being  exposed  to  a  very  gentle  heat  till  it 
becomes  nearly  colorless,  when  it  should  be  diluted  to  a  volume  of 
700  to  800  c.  c.  and  boiled  two  hours  with  occasional  addition  of  a 


718  SPECIAL    PART.  [§  208. 

i'ew  c.  c,  dilute,  previously  heated,  solution  of  sulphurous  acid. 
Titanic  acid  if  present  will  be  precipitated.  After  filtering,  iron 
may  be  determined  in  the  filtrate  by  concentrating,  reducing  with 
1 1. ,S,  boiling  out  excess  of  H2S  and  titrating  with  standard  potas- 
sium permanganate  according  to  §  113,  3,  a. 

It  may  here  be  observed  that  by  proceeding  as  above  directed  r 
in  separating  titanic  acid  from  the  silica  the  traces  of  alumina  and 
possibly  other  basic  oxides  which  may  be  retained  by  the  silica  are 
lost.  This  defect  may  be  remedied,  at  the  expense  of  some  delay, 
by  reserving  the  solution  containing  all  the  basic  metals  as  first 
filtered  from  the  separated'  silica  until  the  sulphuric  acid  solutions 
of  the  titanic  acid  and  other  impurities  possibly  present  in  the  silica 
can  be  obtained  and  added  to  it.  The  iron  and  alumina  precipitate 
will  then  contain  all  the  titanic  acid,  and  the  traces  of  basic  metals 
recovered  from  the  silica  will  be  united  to  the  main  portion.  If 
this  course  is  adopted,  the  use  of  an  unnecessary  amount  of  sodium 
carbonate  and  sulphuric  acid  in  obtaining  a  solution  of  the  residue 
from  the  silica  should  be  avoided.  The  precipitate  of  aluminium 
and  ferric  hydroxides  should,  in  order  to  eliminate  basic  sulphates, 
be  dissolved  and  reprecipitated — a  proceeding  which  is  always 
advisable,  even  in  the  absence  of  sulphates,  when  alkali-earth 
metals  are  present. 

Sulphur.  If  sulphides  are  present  determine  sulphur  as  in 
iron  ores  (see  page  745).  It  must  be  borne  in  mind,  however,  that 
if  barium,  strontium,  or  lead  is  present  a  portion  of  the  sulphuric 
acid  formed  may  be  retained  in  the  undissolved  residue.  By  pro- 
longed boiling  of  this  residue  with  sodium  carbonate  and  filtering, 
the  sulphuric  acid  may  be  brought  into  solution  as  sodium  sul- 
phate. This  solution  may  also  contain  silica  and  lead,  from  which 
the  sulphuric  must  be  separated. 

If  sulphates  are  present  in  the  original  material  along  with  sul- 
phides, the  sulphuric  acid  may  be  determined  by  boiling  a  separate 
portion  a  long  time  with  sodium  carbonate,  filtering,  acidifying  the 
filtrate  with  HC1,  and  precipitating  with  BaCl2.  The  sulphur  in 
the  sulphuric  acid  thus  found,  deducted  from  the  total  amount 
existing  in  both  sulphides  and  sulphates,  leaves  that  belonging  to 
the  sulphides. 

Phosphoric  acid  may  be  determined  as  in  iron  ores  (see  p.  741). 
In  careful  investigations  the  residue  insoluble  in  acids  should  be 
examined  also  by  fusing  it  with  sodium  carbonate,  separating  silica 


§  209.]  SEPARATION    OF    SILICATES.  719 

by  drying  down  with  nitric  acid,  redissolviiig  with  nitric  acid  and 
adding  molybdic  acid  solution.  The  reagents  used  in  this  process 
must  be  free  from  the  least  trace  of  phosphoric  acid.] 


10.    SEPARATION    OF   SILICATES    DECOMPOSABLE 
FROM  THOSE  TOTDECOMPOSABLE  BY  ACIDS. 

§209. 

After  the  silicate  has  been  very  finely  pulverized  and  dried  at 
100°  it  is  usually  treated  for  some  time,  at  a  gentle  heat,  with 
moderately  concentrated  hydrochloric  acid,  evaporated  to  dryness 
on  the  water-bath,  the  residue  moistened  with  hydrochloric  acid, 
water  added,  and  the  solution  filtered  ;  it  is  often  preferable,  how- 
ever, to  digest  the  powder  with  dilute  hydrochloric  acid  (of  about 
1 5  per  cent.)  for  some  days  at  a  gentle  heat,  and  then  at  once  filter 
the  solution.  Which  of  the  two  ways  it  is  advisable  to  adopt,  and 
indeed  whether  the  method  here  described  (which  was  first 
employed  by  CHR.  GMELIX  in  the  analysis  of  phonolites)  may  be 
resorted  to,  depends  Upon  the  nature  of  the  mixed  minerals.  The 
more  readily  decomposable  the  one  of  the  constituent  parts  of  the 
mixture  is,  and  the  less  readily  decomposable  the  other,  the  more 
constant  the  proportion  between  the  undissolved  and  the  dissolved 
part  is  found  to  remain  in  different  experiments  ;  in  other  words, 
the  less  the  undissolved  part  is  affected  by  further  treatment  with 
hydrochloric  acid,  the  more  safely  may  this  method  of  decomposi- 
tion be  resorted  to. 

The  process  gives : 

'/.  A  JtyrfrocMorie  aci^l  solution,  containing,  besides  a  little 
silicic  acid,  the  basic  metals  of  the  decomposed  silicate  in  the  form 
of  metallic  chlorides,  which  are  separated  and  determined  by  the 
proper  methods. 

J.  An  Insoluble  residue,  which  contains,  besides  the  undecom- 
posed  silicate,  the  silica  separated  from  the  decomposed  silicate. 

After  the  latter  has  been  well  washed  with  water,  to  which  a 
few  drops  of  hydrochloric  acid  have  been  added,  transfer  it,  still 
moist,  in  small  portions  at  a  time,  to  a  boiling  solution  of  sodium 
carbonate  (free  from  silicic  acid)  contained  in  a  platinum  dish  ; 
boil  for  some  time,  and  filter  off  each  time,  still  very  hot,  through 
a  weighed  filter.  Finally,  rinse  the  last  particles  of  the  residue 


720  SPECIAL    PART.  [§  209. 

• 

which  still  adhere  to  the  filter  completely  into  the  dish,  and  pro- 
ceed .as  before.  Should  this  operation  not  fully  succeed,  dry  and 
incinerate  the  filter,  transfer  the  ash  to  the  platinum  dish,  and  boil 
repeatedly  with  the  solution  of  sodium  carbonate  till  a  few  drops 
of  the  fluid  finally  passing  through  the  filter  remain  dear  on 
warming  with  excess  of  ammonium  chloride.  "Wash  the  residue, 
first  with  hot  water,  then — to  insure  the  removal  of  every  trace  of 
sodium  carbonate  which  may  still  adhere  to  it — with  water  slightly 
acidified  with  hydrochloric  acid,  and  finally  again  with  pure  water. 
Collect  the  washings  in  a  separate  vessel  (H.  ROSE). 

Acidify  the  alkaline  filtrate  with  hydrochloric  acid,  and  deter- 
mine in  it  the  silicic  acid  which  belongs  to  the  silicate  decomposed 
by  hydrochloric  acid,  as  directed  §  140,  !!.,«.  To  ascertain  how 
much  water  the  part  decomposed  by  acid  contains,  the  following 
data  are  required :  The  percentage  which  the  decomposed  part  is 
of  the  whole,  the  percentage  of  water  in  the  undecomposed  part, 
the  percentage  of  water  in  the  original  mixture  of  silicates.  Dry 
the  nndissolved  silicate  at  100°  and  weigh.  Then  calculate  by 
difference  the  quantity  of  the  dissolved  silicate.  Treat  the  undis- 
solved  silicate  as  directed  §  140,  II.,  ~b.  For  determination  of 
water,  ferrous  iron,  titanic  acid,  and  other  minor  constituents,  see 
8  208. 


11.  ANALYSIS   OF  LIMESTONES,  DOLOMITES, 
MARLS,  &c. 

As  the  minerals  containing  calcium  and  magnesium  carbonates 
play  a  very  important  part  in  manufactures  and  agriculture,  the 
chemist  is  often  called  upon  to  analyze  them.  The  analytical  pro- 
cess differs  according  to  the  different  object  in  view.  For  tech- 
nical purposes,  it  is  sufficient  to  determine  the  principal  constitu- 
ents ;  the  geologist  takes  an  interest  also  in  the  matter  present  in 
smaller  proportions ;  whilst  the  agricultural  chemist  seeks  a  knowl- 
edge not  only  of  the  constituents,  but  also  of  the  state  of  solubility, 
in  different  menstrua,  in  which  they  are  severally  present. 

I  will  give,  in  the  first  place,  a  process  for  effecting  a  complete 
and  accurate  analysis ;  and,  in  the  second  place,  the  volumetric 
methods  by  which  the  calcium  and  magnesium  carbonates  may  be 
determined.  An  accurate  qualitative  examination  should  always 
precede  the  quantitative  analysis. 


§  210.  j     ANALYSIS   OF   LIMESTONES,  DOLOMITES,  MARLS.      721 

A.  METHOD  OF  EFFECTING  THE  COMPLETE  ANALYSIS. 
§210. 

a.  Reduce  a  large  piece  of  the  mineral  to  powder,  mix  this 
uniformly,  and  dry  at  100°. 

1.  Treat  about  2  grm.,  in  a  covered  beaker,  with  dilute  hydro- 
chloric acid  in  excess,  evaporate  to  dryness  in  a  platinum  or  por- 
celain dish,  moisten  the  residue  with  hydrochloric  acid,  heat  with 
water,  filter  on  a  dried  and  weighed  filter,  wash  the  insoluble 
residue,  dry  at  100°,  and  weigh.  It  generally  consists  of  separated 
.y///m,  clay,  and  sand :  but  it  often  contains  also  hurtvu&like  ?//<//- 
tcr.  Opportunity  will  be  afforded  in  y  for  examining  this  residue. 

c.  Mix  the  hydrochloric  acid  solution  with  chlorine  water  [or 
aqueous  solution  of  bromine],  then  with  ammonia  in  slight  excess, 
and  let  the  mixture  stand  at  rest  for  some  time,  in  a  covered  vessel, 
at  a  gentle  heat.    Filter  off  the  precipitate,  which  contains — besides 
the  hydrate  of  sesquioxide  of  manganese,  ferric  and  aluminium 
hydroxides — the  phosphoric  acid  which  the  analyzed  compound 
may  contain,  and,  moreover,  invariably  traces  of  calcium  and  mag- 
nesium ;  wash  slightly,  and  redissolve  in  hydrochloric  acid ;  heat 
the  solution,  add  chlorine  [or  bromine]  water,  and  then  precipitate 
again  with  ammonia;  filter  off  the  precipitate,  wash,  dry,  ignite, 
and  weigh. 

For  the  estimation  of  the  several  components  of  the  precipitate, 
viz.,  iron,  manganese,  aluminium,  and  phosphoric  acid,  opportunity 
will  be  afforded  in  g. 

d.  Unite  the  fluids  filtered  from  the  first  and  second  precipi- 
tates produced  by  ammonia,  and  determine  the  calcium  and  mair- 
nesium  as  directed  in  §  154,  6  (28). 

e.  If  the  limestone  dried  at  100°  still  gives  water  upon  igni- 
tion, this  is  estimated  best  as  directed  §  36. 

f.  Determine  carbonic  acid  by  one  of  the  methods  described  in 
§  139 :  most  accurately  by  absorption  and  weighing  of  liberated 
carbonic  acid,  II.,  £,  page  412,  or  with  simpler  apparatus  by  loss 
of  weight  on  decomposition  with  acid,  II.,  d,  5£,  page  410;  or,  in 
absence  of  water  and  notable  quantities  of  ferrous  iron  and  man- 
ganese, by  fusion  with  vitrified  borax,  II.,  0,  page  408. 

y.  To  effect  the  estimation  of  the  constituents  present  in 
smaller  proportion,  as  well  as  the  analysis  of  the  residue  insoluble 


722  SPECIAL   PAKT.  [§  210, 

in  hydrochloric  acid,  and  of  the  precipitate  produced  by  ammonia, 
dissolve  20 — 50  grrn.  of  the  mineral  in  hydrochloric  acid.  As  the 
evaporation  to  dryness  of  large  quantities  of  fluid  is  always  a 
tedious  operation,  gently  heat  the  solution  for  some  time,  to  expel 
the  carbonic  acid  ;  then  filter  through  a  weighed  filter  into  a  litre 
flask,  wash  the  residue,  dry,  and  weigh  it.  (The  weight  will  not 
quite  agree  with  that  of  the  residue  in  &,  as  the  latter  contains  also 
that  part  of  the  silicic  acid  which  here  still  remains  in  solution.) 

a.  Analysis  of  the  insoluble  Residue. 

ad.  Treat  a  portion  with  boiling  solution  of  pure  sodium  car- 
bonate (§  209,  b),  and  separate  the  silicic  acid  from  the  solution 
(§  140,  II.,  a) ;  this  process  gives  the  quantity  of  that  portion  of 
the  silicic  acid  contained  in  the  residue,  which  is  soluble  in  alka- 
lies. 

bb.  Treat  another  portion,  oy  the  usual  process  for  silicates 
(§  140,  II.,  b),  and  deduct  from  the  silicic  acid  found  the  amount 
obtained  in  aa. 

-  cc.  If  the  residue  contains  organic  matter  (humus),  determine, 
in  a  portion,  the  carbon  by  the  method  of  ultimate  analysis  (§  1TY). 
PETZHOLDT,*  who  determined  by  this  method  the  coloring  organic 
matter  of  several  dolomites,  assumes  that  58  parts  of  carbon 
correspond  to  100  parts  of  organic  substance  (humic  acid). 

dd.  If  the  residue  contains  pyrites^  fuse  another  portion  of  it 
with  sodium  carbonate  and  potassium  nitrate ;  macerate  in  water,, 
add  hydrochloric  acid,  evaporate  to  dryness,  moisten  with  hydro- 
chloric acid,  gently  heat  with  water,  filter,  determine  the  sulphuric 
acid  in  the  filtrate,  and  calculate  from  the  result  the  amount  of 
pyrites  present 4 

ft.  Analysis  of  the  Hydrochloric  Acid  Solution. 
Make  the  solution  up  to  1  litre. 

aa.  For  the  determination  of  the  silicic  acid  that  has  passed 
into  solution,  and  of  the  barium,  strontium,  aluminium,  manga- 

*  Journ.  f.  prakt.  Chem.  63,  194. 

t  Compare  PETZHOLDT,  loc.  cit.;  EBELMEN  (Compt.  rend.  33,  681);  DEVILLE 
(Compt.  rend.  37,  1001;  Journ.  f.  prakt.  Chem.  62,  81);  ROTH  (Journ.  f.  prakt. 
Chem.  58,  84). 

\  If  the  residue  contains  barium  or  strontium  sulphate,  these  compounds  are 
formed  again  upon  evaporating  the  soaked  mass  with  hydrochloric  acid ;  they 
remain  accordingly  on  the  filter,  whilst  the  sulphuric  acid  formed  by  the  sulphur 
of  the  pyrites  passes  into  the  filtrate. 


§  210.]     ANALYSIS   OF   LIMESTONES,  DOLOMITES,  MARLS.       723 

Hfge,  iron,  and  phosphoric  acid,  evaporate  500  c.  c.,  and  dry  the 
residue  at  100° — 110°.  Treat  the  dry  mass,  in  order  to  separate 
silicic  acid,  &c.  (precipitate  I.),  with  hydrochloric  acid  and  water, 
boil  the  solution  with  nitric  acid,  add  ammonia,  boil  till  the  excess 
of  ammonia  has  escaped,  filter,  wash  slightly,  dissolve  on  the  filter 
with  hydrochloric  acid,  reprecipitate  in  the  same  manner  with 
ammonia,  and  filter  off  precipitate  II.,  which  contains  ferric 
hydroxide,  <fec.  Digest  the  united  filtrates  in  a  nearly  filled  and 
closed  flask  with  sulphide  of  ammonium  in  a  slightly  warm  place 
for  24  hours,  then  filter  off  precipitate  III.  This  consists  princi- 
pally of  manganese  sulphide ;  it  is  to  be  washed  with  water  con- 
taining ammonium  sulphide.  Precipitate  the  filtrate  with  ammo- 
nium carbonate  and  ammonia,  allow  to  stand  24  hours,  and  then 
filter  off  precipitate  IY.,  which  consists  for  the  most  part  of  cal- 
cium carbonate,  and  is  to  be  washed  with  water  containing  ammo- 
nia. Evaporate  the  filtrate  in  a  porcelain  dish  to  dryness,  project 
the  residue,  little  by  little,  into  a  red  hot  platinum  dish,  drive  off 
the  ammonium  salts,  moisten  the  residue  with  hydrochloric  acid, 
dissolve  it  in  water,  and  boil,  with  addition  of  pure  milk  of  lime, 
to  strongly  alkaline  reaction.  Filter  off  precipitate  V.,  which  is 
composed  of  magnesium  hydroxide  and  the  excess  of  calcium 
hydroxide,  wash  it,  precipitate  the  filtrate  with  ammonium  carbon- 
ate and  ammonia,  and,  after  long  standing,  filter  off  precipitate  VI., 
which  is  to  be  washed  with  water  containing  ammonia. 

Precipitate  I.  consists  principally  of  silicic  acid.  It  may  also 
contain  barium  and  strontium  sulphates.  Treat  it  in  a  platinum 
dish  with  hydrofluoric  acid  and  a  little  sulphuric  acid,  evaporate 
to  dryness,  and,  if  necessary,  repeat  this  operation.  Should  a  resi- 
due remain,  fuse  it  with  a  small  quantity  of  sodium  carbonate, 
treat  with  water,  filter,  wash,  dissolve  in  hydrochloric  acid,  and 
precipitate  the  solution  with  sulphuric  acid.  When  the  precipitate 
has  settled  filter  it  from  solution  a,  and  wash.  Stop  up  the  tube 
of  the  funnel,  and  fill  the  latter  with  solution  of  ammonium  car- 
bonate, allow  to  stand  12  hours,  open  the  funnel  tube,  wash  the 
residue  first  with  water,  then  with  hydrochloric  acid  (solution  £), 
finally  again  with  water,  and  then  weigh  the  pure  residual  barium 
sulphate.  Mix  the  united  solutions  a  and  ~b  with  ammonium  car- 
bonate and  ammonia,  allow  to  stand  some  time ;  if  a  precipitate 
forms  (which  may  contain  strontium  carbonate)  filter  it  off,  dry, 
and  add  to  precipitate  IV. 


724  SPECIAL    TART.  [§  210. 

Precipitate  II.  consists  principally  of  ferric  hydroxide  ;  it  con- 
tains also  the  aluminium,  and,  provided  there  is  enough  iron,  the 
whole  of  the  phosphoric  acid.  Dissolve  in  hydrochloric  acid,  add 
pure  tartaric  acid,  and  then  ammonia.  Having  fully  convinced 
yourself  that  no  precipitate  is  formed,  precipitate  the  iron  with 
ammonium  sulphide  in  a  small  flask,  which,  must  be  nearly  filled 
and  closed,  allow  to  stand  till  the  fluid  appears  of  a  pure  yellow 
color,  filter,  wash  with  water  containing  ammonium  sulphide,  and 
determine  the  iron  after  §  113,  2.  To  the  filtrate  add  a  little  pure 
sodium  carbonate  and  pure  potassium  nitrate,  evaporate  to  dryness, 
and  ignite  till  the  residue  is  white.  Add  water  and  hydrochloric 
acid  till  the  whole  is  dissolved,*  and  precipitate  the  clear  fluid  with 
ammonia.  If  a  precipitate  forms  (aluminium  hydroxide  or  phos- 
phate, or  a  mixture  of  both),  filter  it  off,  and  weigh.  Mix  the  fil- 
trate with  a  little  magnesium  sulphate.  If  another  precipitate 
forms,  this  time  consisting  of  ammonium  magnesium  phosplnd*' 
(which  is  to  be  determined  after  §  134, 1.,  Z>,  «),  the  aluminium  pre- 
cipitate may  be  calculated  as  aluminium  phosphate  (A12O3,  P2O5). 
If,  on  the  contrary,  no  precipitate  is  formed,  the  phosphoric  acid 
must  be  determined  in  the  alumina  precipitate  as  directed  §  134, 

i.,  i,  ft. 

Precipitate  III.  consists  principally  of  manganese  sulphide. 
It  may  also  contain  traces  of  nickel,  cobalt,  and  zinc  sulphides,  cal- 
cium carbonate,  &c.  Treat  with  moderately  dilute  acetic  acid, 
heat  the  filtrate,  to  remove  any  carbonic  acid,  add  ammonia,  pre- 
cipitate with  ammonium  sulphide,  allow  to  stand  24  hours,  and 
determine  the  manyanese  as  sulphide  (§  109,  2).  If  any  residue 
was  left  insoluble  in  acetic  acid,  test  it  for  the  above-mentioned 
metals.  The  fluid  filtered  from  the  pure  manganese  sulphide  is  to 
be  mixed  with  ammonium  carbonate.  If  a  precipitate  forms  it  is 
to  be  treated  with  precipitate  IY. 

Precipitate*  IV.,  V.,VI.  The  united  mass  of  these  precipi- 
tates, together  with  the  small  portions  of  alkali-earth  carbonates 
obtained  during  the  treatment  of  precipitates  I.  and  III.  contain 
the  whole  of  the  strontium  and  the  whole  of  the  barium  which 
originally  passed  into  the  hydrochloric  acid  solution.  Ignite  the 
dried  precipitate  (if  necessary  in  portions)  in  a  platinum  crucible, 
most  intensely  over  the  gas  blowpipe.  By  this  means  any  barium 

*  I  may  remind  the  operator  that  the  residue,  which  contains  nitric  acid,  can- 
not he  heated  with  hydrochloric  acid  in  a  plntimim  dish. 


§  210.]     AXALYSIS    OF    LIM*;STONKS,    DOLOMITES,   MARLS.       735 

and  strontium  carbonate!?,  and  a  part,  at  all  events,  of  the  calcium 
carbonate,  are  converted  into  oxides  (ENGELBACH*).  Boil  the  resi- 
due 5  or  6  times  with  small  portions  of  water,  pouring  oif  the  solu- 
tion through  a  filter  ;  neutralize  the  solution  with  hydrochloric 
acid,  evaporate  to  dry  ness,  and  test  a  minute  portion  with  the 
spectroscope  —  this  minute  portion  is  afterwards  added  to  the  rest. 
If  calcium  and  strontium  alone  are  present,  separate  according  to 
26.  If  barium  is  present,  separate  the  three  alkali-earth  metals 
after  23. 

l>b.  Although  it  is  possible  in  aa  to  test  for  metals  precipitable 
by  hydrogen  sulphide  from  acid  solution,  e.g.,  copper,  and  if 
required  to  determine  them,  still  it  is  more  convenient  to  employ 
a  fresh  quarter  of  the  hydrochloric  acid  solution  for  this  purpose. 
The  precipitate  obtained  by  passing  the  gas  into  the  warm  dilute 
solution  is  washed,  dried,  and  treated  with  carbon  disulphide.  If 
a  residue  remains  it  is  to  be  examined. 

re.  The  remaining  quarter  of  the  dilute  hydrochloric  acid  solu- 
tion is  used  for  the  estimation  of  the  alkalies.^  Mix  with  chlo- 
rine water,  then  with  ammonia  and  ammonium  carbonate  ;  after 
allowing  the  mixture  to  stand  for  some  time,~filter  off  the  precipi- 
tate, evaporate  the  filtrate  to  dryness,  ignite  the  residue  in  a  plati- 
num dish  to  remove  the  ammonium  salts,  and  finally  separate  the 
magnesium  from  the  alkalies  as  directed  p.  491,  15.  The  reagents 
must  be  most  carefully  tested  for  fixed  alkalies,  and  the  use  of  glass 
and  porcelain  vessels  avoided  as  far  as  practicable. 

Should  the  limestone  contain  a  sulphate  soluble  in  hydrochloric 
acid,  precipitate  the  sulphuric  acid  by  a  small  excess  of  barium 
chloride,  allow  to  settle,  and  filter  off  the  barium  sulphate  (which 
is  to  be  determined  in  the  usual  manner)  before  proceeding  as 
above  to  the  estimation  of  the  alkalies. 

//.  As  calcite  and  aragonite  may  contain  fluorides 


*  Zeitschr.  f.  anal.  Chem.  1,  474. 

\  The  simplest  way  of  ascertaining  whether  and  what  alkalies  are  present  in 
a  limestone,  is  the  process  given  by  ENGELBACH  (Annal.  d.  Chem.  u.  Pharm.  123, 
260)—  viz.,  ignite  a  portion  of  the  triturated  mineral  strongly  in  a  platinum  cru- 
cible over  the  blast,  boil  with  a  little  water,  filter,  neutralize  with  hydrochloric 
acid,  precipitate  with  ammonia  and  ammonium  carbonate,  filter,  evaporate  the 
nitrate  to  dryness  and  examine  with  the  spectroscope.  The  ammonium  carbon- 
ate precipitate  may  be  evaporated  with  hydrochloric  acid  to  dryness,  and  exam 
ined  in  like  manner  for  barium  and  strontium. 

J  Pogg.  Annal.  96,  145. 


726  SPECIAL   PAKT.  [§  211. 

the  possible  presence  of  fluorine  must  not  be  disregarded  in  accu- 
rate analyses  of  limestones.  Treat,  therefore,  a  larger  sample  of 
the  mineral  with  acetic  acid  until  the  calcium  and  magnesium  car- 
bonates are  decomposed  ;  evaporate  to  dryness  until  the  excess  of 
acetic  acid  is  completely  expelled,  and  extract  the  residue  with 
water  (§  138,  I.).  We  have  the  fluorine  in  the  residue.  If  it  can 
be  distinctly  detected  in  a  portion  of  the  same,*  the  determination 
may  be  attempted  after  §  138,  II.,  3,  a. 

i.  If  the  limestone  under  examination  contains  chlorides,  treat 
a  large  sample  with  water  and  nitric  acid,  at  a  very  gentle  heat ; 
filter,  and  precipitate  the  chlorine  from  the  filtrate  by  solution  of 
silver  nitrate. 

k.  It  is  often  interesting  for  agriculturists  to  know  the  degree 
of  solubility  of  a  sample  of  limestone  or  marl  in  the  weaker  solv- 
ents. This  may  be  ascertained  by  treating  the  sample  first  with 
water,  then  with  acetic  acid,  finally  with  hydrochloric  acid,  and 
examining  each  solution  and  the  residue.  The  analysis  of  marls 
made  by  C.  STRUCKMANNf  were  done  in  this  manner. 

I.  To  effect  the  separation  of  the  caustic  or  carbonated  lime,  in 
hydraulic  limes,  from  the  silicates,  DEVILLED  proposed  to  boil  with 
solution  of  ammonium  nitrate,  which  he  stated  would  dissolve  the 
caustic  lime  and  carbonate  of  lime,  without  exercising  a  decom- 
posing action  on  the  silicates.  GUNNING§  found,  however,  that  by 
this  process  the  double  silicates  of  aluminium  and  calcium  are  more 
or  less  decomposed,  with  separation  of  silicic  acid.  As  yet  no 
method  is  known  by  which  the  object  here  stated  can  be  accom- 
plished with  absolute  accuracy ;  the  best  way,  perhaps,  is  treating 
the  sample  with  dilute  acetic  acid ;  C.  KNAUSZ  |  recommends 
hydrochloric  acid. 

B.  VOLUMETRIC  DETERMINATION  OF  CALCIUM  CARBONATE  AND  MAG- 
NESIUM CARBONATE  (for  technical  purposes). 

§  211. 

a.  If  a  mineral  contains  only  calcium  carbonate,  the  amount  of 
the  latter  may  be  estimated  from  the  quantity  of  acid  required  to 

*  See  Qual.  Anal.  §  146,  6.  f  Annal.  d.  Chem.  u.  Pharm.  74,  170. 

\  Compt.  rend.  37,  1001;  Journ.  f.  prakt.  Chem.  62,  81. 

§  Journ!  f.  prakt.  Chem.  62,  318. 

I  Gewerbeblatt  aus  Wttrtcmbera:,  1855,  Nr.  4;  Chem.  Oentralbl.,  1855,  244. 


ANALYSIS    OF    LIMESTONES,   DOLOMITES,   MARLS.       7*27 

Affect  its  decomposition,  the  method  described  in  §  198  being 
•employed  for  the  purpose.  Or  the  carbonic  acid  in  the  mineral 
may  be  determined,  and  1  mol.  calcium  carbonate  =  100  calculated 
for  each  mol.  carbonic  acid  =  44. 

J>.  But  if  the  mineral  contains,  besides  calcium  carbonate,  also 
magnesium  carbonate,  the  results  obtained  by  either  process  give 
the  quantity  of  calcium  carbonate  -f-  magnesium  carbonate,  the 
latter  being  expressed  by  its  equivalent  quantity  of  calcium  car- 
bonate (/.<".,  100  of  calcium  carbonate  for  84  of  magnesium  carbon- 
ate ').  If,  therefore,  you  desire  to  know  the  actual  amount  of  each, 
YOU  must,  in  addition  to  the  above  determination,  determine  one 
of  the  alkali-earth  metals  separately.  For  this  purpose  one  of  the 
two  following  methods  may  be  employed  : — 

1.  Mix  the  dilute  solution  of  2 — 5  grm.  of  the  mineral  with 
ammonia  and  ammonium  oxalate  in  excess,  allow  to  stand  for  12 
hours  and  then  filter.  Ignite  the  precipitate  of  calcium  oxalate, 
together  with  the  filter,  and  treat  the  calcium  carbonate  produced 
as  directed  §  198.  This  process  gives  the  amount  of  calcium  con- 
tained in  the  analyzed  mineral ;  the  difference  between  this  and 
the  former  result  gives  the  calcium  carbonate  which  is  equivalent 
to  the  amount  of  magnesium  carbonate  present.  To  obtain  per- 
fectly accurate  results  by  this  method,  repeated  precipitation  is 
indispensable  (see  §  154,  6,  a). 

"2.  Dissolve  2 — 5  grm.  of  the  mineral  in  the  least  possible 
excess  of  hydrochloric  acid,  and  add  a  solution  of  lime  in  sugar 
water  as  long  as  a  precipitate  forms.  By  this  operation  the  mag- 
nesia only  is  precipitated.  Filter,  wash,  and  treat  the  precipitate 
as  directed  §  198  ;  the  result  represents  the  quantity  of  the  magne- 
sium. Deduct  the  quantity  of  calcium  carbonate  equivalent  thereto 
from  the  result  of  the  total  determination ;  the  remainder  is  the 
amount  of  calcium  carbonate  present. 

The  method  2  is  only  suitable  when  the  proportion  of  magne- 
sium is  small. 


728  SPECIAL    PART.  [§  212. 

[12.  A8SAY  OF  COPPER  ORES. 
§  212. 

For  the  assayer  who  has  occasion  to  determine  the  amount  of 
copper  in  ores  very  frequently,  the  method  of  LTTCKOW*  depending- 
on  the  electrolytic  deposition  of  copper,  and  the  method  of  STEIN- 
BECK^ (volumetric  determination  by  means  of  potassium  cyanide), 
are  to  be  recommended.  For  the  analytical  chemist,  who  is  only 
occasionally  called  upon  to  assay  a  copper  ore,  the  processes 
below  described  may  be  useful,  as  they  require  no  preparation  of 
special  reagents  or  apparatus. 

1.  When  Arsenic,  Antimony,  Bismuth,  (Cadmium,  Tin)  are 
not  present. 

Take  1  grm.  of  the  pulverized  ore  if  rich,  3  to  5  if  poor.  Put 
it  in  a  dry  beaker  (best  of  a  diameter  of  8 — 10  centimetres  at  the 
bottom),  cover  with  a  watch-glass.  Mix  in  another  glass  vessel, 
which  should  be  dry  to  avoid  dilution,  1  pt.  sulphuric  with  3  to  -t 
pts.  nitric  acid,  both  concentrated.  Pour  the  mixed  acids  upon  the 
ore.  40 — 50  c.  c.  will  suffice  if  not  more  than  2  grm.  ore  are  taken. 
The  action  is  less  violent  if  the  requisite  amount  of  acid  is  added 
at  once  than  it  is  if  added  gradually.  Heat  the  covered  beaker  011 
a  sand-bath,  to  near  100°  C.  an  hour  or  two,  or  until  the  action  of 
the  acids  on  the  ore  has  apparently  nearly  ceased,  raise  then  the  watch- 
glass  covering  the  beaker  so  far  as  to  allow  vapors  to  pass  off  freely 
by  interposing  between  it  and  the  beaker  a  triangle  made  of  thick 
glass  rod,  and  evaporate  until  nitric  acid  is  completely  removed. 
Copper  exists  in  the  residue  as  sulphate,  mixed  usually  with  other 
metallic  sulphates,  together  with  such  constituents  of  the  ore  as  are 
not  decomposed  by  the  acids.  A  small  quantity  of  liquid  (sulphuric 
acid)  will  still  remain  with  the  solid  residue,  and  should  not  be 
removed  by  further  elevation  of  temperature.  After  cooling,  add 
about  100  c.  c.  of  water  to  the  residue  and  keep  it  warm  on  the 
sand-bath  an  hour  to  ensure  solution  of  the  anhydrous  copper  sul- 
phate. Complete  solution  of  the  copper  in  the  residue  may  be 
effected  in  a  few  minutes  by  adding  with  the  water  a  little  hydro- 
chloric acid;  but  since  hydrochloric  acid  dissolves  notable  quantities 
of  lead  sulphate,  it  should  not  be  used  for  this  purpose  unless  the 
ore  is  known  to  be  free  from  lead.  Filter  from  the  undissolved 


Zeitschr.  f.  anal.  Cliem.  8,  28.,  and  11,  1.  \  Ib.  8,  9.. 


§  212.]  ASSAY   OF   COPPER    ORES. 

part  of  the  residue  and  wash  it  with  hot  water.  If  the  residue 
contains  lead  sulphate,  avoid  the  use  of  an  unnecessary  volume  of 
water  in  washing,  or  use  water  acidified  with  sulphuric  acid  to  pre- 
vent lead  sulphate  from  being  dissolved.  Dilute  the  filtrate  to 
about  500  c.  c.  If  hydrochloric  acid  has  not  previously  been  used, 
add  now  1  or  2  c.  c.  and  heat  to  boiling  and  pass  hydrogen  sulphide 
through  the  solution  until  the  copper  is  all  precipitated,  the  tem- 
perature meanwhile  being  maintained  nearly  or  quite  to  the  boil- 
ing point.  If  a  tolerably  rapid  current  of  H2S  be  passed  into  the 
solution  through  a  tube  contracted  at  the  orifice  to  a  diameter  of  1 
to  2  millimetres,  so  as  to  produce  numerous  and  small  bubbles,  the 
precipitation  is  usually  complete  in  course  of  15  to  25  minutes. 
Wash  the  precipitate,  dry,  ignite  in  an  atmosphere  of  hydrogen,  and 
weigh  the  resulting' CuaS  according  to  directions  in  §  111*.  :>.  «, 
page  316. 

2.    When  Antimony,  Arsenic,  (Bismuth,  Cadmium,  Tin  \  <n->- 
present. 

Arsenical  or  antimonial  minerals  are  occasionally  present  in 
copper  ores,  bismuth  compounds  very  rarely,  while  appreciable 
amounts  of  cadmium  or  tin  can  usually  safely  be  assumed  to  be 
absent.  If  the  ore  to  be  assayed  has  not  been  pulverized  and  can 
be  examined  in  large  fragments,  the  assayer,  with  sufficient  knowl- 
edge of  mineralogy  and  experience  in  the  use  of  the  blowpipe,  can 
usually  decide  whether  arsenic,  antimony,  or  even  bismuth  are 
present.  If  this  cannot  be  done,  qualitative  testing  in  the  wet  way 
should  be  resorted  to.  If  any  of  the  metals  which  interfere  with 
the  process  described  in  1  are  present,  decompose  the  ore  with 
aqua  regia,  adding  also  enough  sulphuric  acid  to  convert  into  sul- 
phates, on  evaporation,  any  nitrates  and  chlorides  which  may  be 
formed.  An  unnecessary  excess  of  sulphuric  should  be  avoided,, 
as  it  is  difficult  to  remove  by  evaporation  and,  if  allowed  to  remain 
in  large  amount,  may  render  the  subsequent  precipitation  of  copper 
less  perfect.  After  removing  the  nitric  and  hydrochloric  acids- 
by  evaporation,  dissolve  the  copper  sulphate  in  the  residue  by 
digestion  with  water,  filter,  add  solution  of  sulphurous  acid  (100 — 
200  c.  c.),  set  in  a  warm,  place  ;  if  the  solution  ceases  to  smell  of  SOZ 
after  half  an  hour,  add  more  solution  of  sulphurous  acid.  Finally, 
after  allowing  the  solution  to  stand  in  a  warm  place  -t  or  5  hours 
at  least,  precipitate  the  copper  with  ammonium  or  potassium  sul- 
phocyanate  and  determine  it  as  C'n,S  as  directed  in  §  119,  3.  I. 


730  SPECIAL    PART.  [§213. 

[13.  ASSAY  OF   LEAD  ORES 
§  213. 

The  commercial  value  of  lead  ore  is  often  estimated  from 
assays  made  in  the  dry  way.  These  assays  are  not  very  exact  even 
in  rich  ore,  and  still  less  so  in  poor  ores.  If  the  means  for  making 
a  dry  assay  are  not  at  hand,  or  a  more  accurate  determination  is 
required,  the  following  method  applicable  to  all  ores  (rich  or  poor, 
galenas  or  carbonates),  not  containing  arsenic  or  antimony  may  be 
used. 

Decompose  the  finely  pulverized  ore — 2  grin,  if  rich,  5  grm.  if 
poor — with  a  mixture  of  concentrated  nitric  and  sulphuric  acid 
precisely  in  the  manner  described  for  copper  ores  (§  212,  1). 
After  free  nitric  acid  has  been  removed  by  evaporation,  the  lead 
exists  in  the  residue  as  lead  sulphate,  mixed,  according  to  the  char- 
acter of  the  ore,  with  different  kinds  and  quantities  of  other 
metallic  sulphates,  and  also  such  constituents  of  the  ore  as  are  not 
decomposed  by  the  acids.  Sulphuric  acid,  which  may  be  used 
freely  in  the  decomposing  mixture,  should  remain  also  with  this 
residue  and  not  be  driven  off  by  evaporation.  When,  toward  the 
•close  of  the  process  of  evaporation  by  gradually  increasing  tem- 
perature, dense  white  fumes  of  sulphuric  acid  begin  to  appeal-,  or 
when,  at  a  temperature  little  exceeding  100°  C.,  no  odor  of  nitric 
acid  is  perceptible,  heat  is  removed  and  the  residue  allowed  to 
cool.  About  100  c.  c.  of  water  are  then  added.  After  digesting  2 
hours  to  dissolve  such  metallic  sulphates  as  are  soluble  in  water,' 
the  residue,  containing  lead  sulphate  and  other  insoluble  matter 
(possibly,  for  example,  quartz,  native  silicates,  barium  sulphate, 
calcium  sulphate),  is  collected  on  a  moderate  sized  filter  and  washed 
with  water  to  which  a  little  sulphuric  acid  has  been  added.  The 
filter  and  its  contents,  without  previous  drying,  are  then  placed  in 
the  bottom  of  a  large  beaker.  Pour  first  ammonia  (20 — 30  c.  c.) 
upon  the  filter  and  residue,  and  next  acetic  acid  to  decided  acid  reac- 
tion, keep  warm  some  20  minutes  with  occasional  stirring.  The 
lead  sulphate  readily  dissolves.  Filter,  wash  the  still  remaining 
undissolved  residue  and  filter,  chiefly  by  decantation,  adding  to 
the  wash  water  at  first  a  little  ammonium  acetate.  The  filtrate  may 
contain,  besides  lead,  also  calcium  sulphate.  To  prevent  the  possi- 


$  214.]  NICKEL   AND   COBALT   IN    ORKS.  731 

ble  deposition  of  the  latter  during  the  subsequent  precipitation  of 
the  lead,  dilute  the  filtrate  by  adding  ^  to  1  its  volume  of  water, 
and  add  1  or  2  c.  c.  dilute  hydrochloric  acid.  Precipitate  now  the 
lead,  either  in  the  cold  or  slightly  heated  solution,  with  a  current 
•of  hydrogen  sulphide.  Treat  the  precipitate  according  to  §  11(>,  '2 
page  299.  In  igniting  in  hydrogen,  take  care  that  only  the  bot- 
tom of  the  porcelain  crucible  is  faintly  red.  Too  high  heat  will 
cause  loss  by  volatilization. 

If  this  ore  contains  arsenic  and  antimony,  these  elements,  or  at 
least  the  latter,  will  cause  a  small  quantity  of 'lead  to  remain  undis- 
solved  in  the  residue  remaining  after  the  treatment  with  ammo- 
nium acetate.  In  such  a  case,  lead  may  be  separated  from  the  resi- 
due by  means  of  methods  of  separation  described  in  §  164,  or  a 
wholly  different  course  may  be  devised  and  applied  to  the  original 
substance.]  ' 

[14.  DETERMINATION  OF  NICKEL  AND  COBALT  IN 
ORES.     SPEISS*  AND  MATTE.f 

§  214. 

The  separation  of  nickel  and  cobalt  from  other  metals  which 
accompany  them  in  ores  and  determination  of  their  joint  amount 
precedes  the  separation  of  the  two  metals.  The  process  requires 
great  care  throughout.  A  method  is  here  given  for  determining  these 
metals,  and  also  copper  and  lead,  in  a  "  matte"  containing,  besides 
nickel  and  cobalt,  copper,  lead,  iron,  and  accidental  adhering  parti- 
cles of  sand  and  earthy  silicates.  To  the  description  of  this  method 
will  be  appended  modifications  necessary  or  admissible  in  the 
examination  of  other  products. 

1.  Decomposition  and  Separation  of  Lead. 

Decompose  2  gr.  of  the  very  finely  pulverized  material  with  a 
mixture  of  concentrated  nitric  and  sulphuric  acid,  proceeding  pre- 
cisely as  recommended  for  decomposition  of  copper  ores.  (See  ^ 
212,  1.)  It  is,  however,  safer,  after  the  nitric  acid  first  employed 

*  A  product  consisting  chiefly  of  metallic  arsenides  obtained  by  smelting  ores 
is  called  "speiss." 

.  f  A  product  consisting  chiefly  of  metallic  sulphides  obtained  by  smelting  ores 
is  called  "matte." 


732  SPECIAL   PABT.  [§  214. 

has  been  expelled,  to  add  to  the  residual  sulphuric  acid  a  fresh  por- 
tion of  concentrated  nitric  acid  ;  keep  hot  for  some  time,  and  finally 
evaporate  off  all  the  nitric  acid  a  second  time,  allowing  at  least  8 
or  10  hours  for  the  whole  process  of  decomposition.  Add  water 
(100  to  150  c.c.)  to  the  cooled  residue  and  digest  3  or  4  hours,  and 
filter  the  solution  of  metallic  sulphates  obtained  from  the  insolu- 
ble residue,  which  contains  the  lead  as  sulphate,  together  with  par- 
ticles of  sand,  &c.  Dissolve  the  lead  sulphate  in  this  residue  with 
ammonium  acetate  and  determine  the  lead  as  in  the  process  of  assay- 
ing lead  ores,  §213.  Incinerate  the  filter  containing  the  portion  of 
the  residue  which  ammonium  acetate  fails  to  dissolve  in  a  porcelain 
crucible,  and  add  to  it  in  the  crucible  aqua  regi#  ;  evaporate  to  a 
few  drops.  If  the  few  drops  of  remaining  liquid  show  no  greenish 
color,  it  may  be  assumed  that  the  residue  so  treated  contains  no 
nickel  or  cobalt. '  If  the  color  indicates  presence  of  these  metals,  rinse 
the  contents  of  the  crucible  into  the  filtrate  from  the  lead  sulphate. 
Before  throwing  away  the  filtrate  from  the  final  lead  precipitate  (lead 
sulphide),  prove  that  it  contains  no  nickel  or  cobalt  by  adding  ammo- 
nia to  neutral  reaction,  and  a  few  drops  of  ammonium  sulphide. 

2.  Separation  of  Copper. 

Dilute  the  filtrate  from  the  lead  sulphate  and  other  insoluble 
matter  to  about  500  c.c.,  and  precipitate  copper  with  hydrogen  sul- 
phide and  determine  it,  proceeding  as  directed  in  "Assay  of  Copper 
Ores,"  §  212. 

3.  Separation  of  Iron. 

Concentrate  the  filtrate  from  the  copper  sulphide,  add  nitric 
acid  enough  to  convert  the  iron  into  a  ferric  salt,  and  boil  a  few 
minutes.  Allow  the  solution,  which  should  now  occupy  a  volume 
of  about  300  c.c.,  to  become  nearly  cold,  and  add  a  large  twcss  of 
ammonia  at  once,  and  let  it  stand  in  a  warm  place  (50°  to  70°  C.)  half 
an  hour.  Filter  then  into  a  porcelain  casserole  and  wash  the  greater 
part  of  the  saline  matter  out  of  the  ferric  hydroxide  with  hot  water. 
Complete  washing  is  needless.  Although  this  filtrate  contains  the 
greater  part  of  the  nickel  and  cobalt,  a  very  considerable  quantity 
is  retained  by  the  ferric  hydroxide.  Even  a  second  precipitation 
with  ammonia  cannot  be  relied  upon  for  effecting  a  satisfactory  sep- 
aration. Dissolve,  therefore,  the  ferric  hydroxide  in  hydrochloric 
acid,  which  may  be  used  freely  for  this  purpose,  since  it  will  be 


NICKEL    AM)    COBALT    IX    OKKS.  733 

next  converted  into  ammonium  ,  chloride,  which  acts  favorably, 
rather  than  otherwise,  in  the  subsequent  precipitation  of  iron 
(§  160,  71).  Wash  the  filter  from  which  the  iron  precipitate  has 
been  dissolved,  neutralize  the  greater  part  of  the  free  hydro- 
chloric acid  in  the  solution  with  ammonia,  proceed  then  care- 
fully to  prepare  the  solution  for  precipitation  of  iron  with  sodium 
cwetate  by  neutralizing  properly  with  sodium  or  ammonium  car- 
bonate and  addition  of  acetic  acid,  as  described  in  §  160,  71,  p.  517. 
The  iron  precipitated  thus  a  second  time  is  still  not  absolutely  free 
from  a  trace  of  nickel  or  cobalt,  which  may,  however,  be  neglected 
unless  extraordinary  accuracy  is  required,  or  unless  the  original  sub- 
stance was  comparatively  rich  in  these  metals  (containing  over  2<> 
per  cent).  In  that  case,  dissolve  the  iron  precipitate  in  hydrochlo- 
ric acid  and  precipitate  the  iron  again  as  basic  ferric  acetate  and 
filter.  Add  the  filtrate  or  filtrates,  as  the  case  may  be,  to  the  first 
ammoniacal  filtrate,  which  should  meanwhile  have  been  concen- 
trated to  expel  free  ammonia  and  reduce  its  volume.  The  mixed 
filtrates  will  now  contain  some  free  acetic  acid.  Concentrate  in  a 
porcelain  dish  to  300  or  400  c.c.,  and  add  ammonia  to  alkaline  reac- 
tion. This  will  usually  throw  down  a  little  ferric  or  aluminium 
hydroxide,  which  is  to  be  filtered  off.  If  the  precipitate  is  very 
slight  it  may  be  thrown  aw^ay.  If  considerable,  dissolve  in  HC1, 
re  precipitate  with  ammonia,  filter,  and  add  the  filtrate  to  the  main 
filtrate. 


4.  Precipitation  <>f  JT/V^v-/  ////</  Cobalt. 

Concentrate  the  now  alkaline  solution  to  a  volume  of  about  250 
c.c.  During  the  concentration  the  solution  will  sometimes  become 
slightly  acid,  as  may  be  shown  by  testing  with  litmus  paper.  If 
acid,  it  is  in  just  the  right  condition  for  precipitation  of  nickel  and 
cobalt  as  sulphides.  If  alkaline,  add  cautiously  HC1  till  the  fluid 
gives  with  litmus  paper  a  distinct  but  slight  acid  reaction.  Pre- 
cipitate next  nickel  and  cobalt  in  the  solution  previously  heated 
to  gentle  ebullition  in  a  beaker  covered  with  a  watch-glass,  with 
hydrogen  sulphide,  according  to  §  110,  J,  /?,  p.  261.  Dry  the  sul- 
phides on  the  filter  and  remove  them  from  the  filter  to  a  beaker. 
Incinerate  the  filter,  add  the  ash  and  adhering  nickel  and  cobalt 
sulphides  to  the  portion  in  the  beaker,  or  if  the  whole  quantity  of 
sulphides  is  small,  calcine  the  whole  with  the  filter.  Treat  with 


734  SPECIAL   PART.  [§  214, 

aqua  regia  until  only  a  residue  of  yellow  sulphur  remains  undis- 
solved,  evaporate,  and  expose  the  residue  to  a  heat  of  100°  C.,  to 
make  traces  of  silica  insoluble ;  then  moisten  with  a  few  drops  of 
hydrochloric  acid,  add  15 — 20  c.c.  of  water  to  dissolve  nickel  and 
cobalt  salts,  add  without  previous  filtration  some  fresh  solution 
of  H2S  as  long  as  it  produces  a  dark-colored  precipitate  or  turbid- 
ity (indicating  traces  of  still  unremoved  copper  or  lead),  filter  into 
a  porcelain  dish  (having  a  capacity  of  250  c.c.),  and  concentrate  the 
solution  to  about  100  c.c.  Boil  gently,  and  during  the  boiling  add 
gradually  pure  sodium  carbonate  solution  to  alkaline  reaction, 
avoiding  much  excess ;  continue  the  boiling  a  few  minutes  to- 
remove  free  carbonic  acid.  Next  dissolve  in  a" platinum  dish  a  few 
decigrammes  of  pure  sodium  hydroxide  (prepared  from  metallic 
sodium*),  add  the  solution,  and  heat  again  to  boiling  to  -precipitate 
the  nickel  and  cobalt  that  may  still  remain  in  solution.  Wash  the 
precipitate  with  boiling  hot  water,  first  by  decantation,  and  finally 
on  the  filter  (best  with  the  BUNSEN  filtering  apparatus)  until  a  drop 
of  the  washings  evaporated  on  polished  platinum  foil  gives  no- 
more  residue  than  distilled  water,  and  then  wash  still  a  little  longer. 
After  drying  the  precipitate,  remove  from  the  filter  to  a  piece  of 
glazed  paper,  and  cover  it  immediately  with  a  bell-glassf  and  incin- 
erate the  filter  with  the  small  portion  adhering  to  it  until  carbon 
is  completely  removed,  and  expose  for  some  time  longer  to  the 
air  at  a  red  heat,  to  remove  traces  of  carbon  which  metallic  nickel 
reduced  by  the  paper  may  have  absorbed.  Transfer  the  main  por- 
tion of  the  oxides  to  the  crucible,  cover  and  heat  to  redness,  finally 
reduce  the  oxides  to  metals  by  ignition  in  hydrogen,  according  to 
§  110,  2. 

If  the  preceding  operations  have  been  conducted  with  due  care 
the  metals  thus  obtained  are  free  from  appreciable  quantities  of 
impurities.  Test  them,  however,  first  for  soda  by  adding  in  the 
crucible  a  few  drops  of  water,  allowing  it  to  remain  in  contact  with 
the  metal  10  minutes  or  longer,  and  applying  reddened  litmus 
paper.  If  the  experiment  shows  presence  of  soda  it  can  be  removed 
(probably  but  incompletely)  by  prolonged  digestion  with  water, 

*  If  pure  sodium  hydroxide  is  not  at  hand,  a  small  quantity  can  easily  be  pre- 
pared by  dissolving  a  fragment  of  sodium  in  water  in  a  platinum  dish. 

t  Strongly  dried  mckelous  hydroxide  exposed  to  moist  air  will  often  decrepi- 
tate projecting  particles  a  considerable  distance. 


§  214.]  NICKEL   AND    CDBALT   IN    ORES.  735 

removing  the  water  with  a  pipette,  drying  and  igniting  the  metal 
again  in  hydrogen.  Test  also  for  silica  by  dissolving  in  nitric  acid. 
If  an  appreciable  amount  of  silica  remains  undissolved,*  collect  on 
a  small  filter,  weigh,  and  make  the  necessary  deduction  from  the 
first  weight  of  the  metals. 

5.  Separation  of  Cobalt  from  Nickel. 

Evaporate  the  nitric  acid  solution  of  the  metals  nearly  to  dry- 
ness,  or  until  free  nitric  is  almost  completely  removed  ;  add  4  or  5 
c.c.  of  water  to  dissolve  the  nickel  and  cobalt  salts,  add  drop  by 
drop  solution  of  potassium  carbonate  until  a  permanent  precipitate 
just  begins  to  be  formed.  (If  free  nitric  has  been  removed  by 
evaporation  completely,  the  addition  of  potassium  carbonate  is  not 
required.)  Next  add  6  to  8  gnn.  potassium  nitrite  dissolved  in  10  to 
15  c.c.  of  hot  water.  This  usually  produces  a  flocculent  precipi- 
tate containing  both  nickel  and  cobalt,  on  account  of  the  potassium 
carbonate  wrhich  the  nitrite  commonly  used  as  a  reagent  contains. 
Add  then  a  little  acetic  acid.  Any  flocculent  precipitate  which 
may  have  been  previously  formed  now  disappears,  and  a  precipitate 
of  tri potassium  cobaltic  nitrite,  either  simultaneously  or  after  a 
short  time,  is  deposited.  Much  acetic  acid  hinders  the  complete  sep- 
aration of  cobalt.  If  a  flocculent  precipitate  has  been  formed,  a  few 
drops  usually  suffice  to  dissolve  it ;  2  or  3  c.c.  more  may  then  be 
added.  The  whole  volume  of  the  solution  should  then  amount  to 
only  15  to  20  c.c.  Cover  the  beaker  containing  it  with  a  watch- 
glass  and  allow  it  to  stand  in  a  warm  place  at  least  24  hours.  Fil- 
ter ;  wash  with  a  solution  of  potassium  acetate,  f  Test  the  filtrate 
for  cobalt  as  follows  :  Dilute,  heat,  precipitate  with  sodium  hydrox- 

*  According  to  my  own  experience  it  is  not  difficult  to  obtain  the  nickel  and 
cobalt  free  from  iron  and  aluminium.  If  the  operator  wishes  to  assure  himself 
on  this  point,  an  excess  of  ammonia  may  be  added  to  the  nitric  acid  solution 
bef ore  filtering  off  the  silica.  If  a  precipitate  is  formed  it  must  be  collected  on  a 
filter,  washed  slightly,  dissolved  on  the  filter  (which  retains  the  accompanying- 
silica),  reprecipitated  with  ammonia,  collected  again  on  the  same  filter,  washed, 
ignited,  and  weighed,  when  its  weight  jointly  with  the  silica  may  be  deducted 
from  the  first  weight  of  the  cobalt  and  nickel.  If  cobalt  is  then  to  be  separated 
from  nickel,  both  metals  may  be  precipitated  from  the  filtrates  as  sulphides,  dis- 
solved in  aqua  regia,  when  after  removing  free  acids,  the  process  of  separating 
cobalt  may  be  applied. — O.  D.  A. 

f  A  suitable  solution  may  be  prepared  by  neutralizing  acetic  acid  with  crys- 
tallized potassium  bicarbonate,  leaving  the  solution  slightly  acid. 


736  SPECIAL   PART.  [§  214. 

ide,  wash  the  greater  part  of  the  saline  matter  out  of  the  precipi- 
tate, dissolve  it  in  nitric  acid,  evaporate  to  dryness  on  a  water-bath, 
add  two  or  three  drops  of  nitric  acid  to  the  residue,  dissolve  in  a 
small  volume  of  water,  filter,  concentrate,  and  repeat  the  process 
of  separation  with  potassium  nitrite  as  before.  Put  the  filter  con- 
taining the  cobalt  precipitate,  still  moist,  into  a  beaker,  add  about 
100  c.c.  of  water,  heat,  add  hydrochloric  acid  until  solution  is 
effected,  separate  the  filter  paper  by  filtration,  evaporate  the  solu- 
tion on  a  water-bath,  allowing  the  residue  to  remain  on  the 
water-bath  2  or  3  hours  to  render  traces  of  silica  insoluble, 
moisten  with  hydrochloric  acid,  add  water,  filter,  and  convert 
the  cobalt  in  the  solution  into  the  metallic  form  by  the  same 
process  as  before  employed  for  obtaining  metallic  nickel  and 
cobalt  from  a  similar  solution  ;  test  also  the  weighed  cobalt  for 
impurities  in  the  same  manner.  The  amount  of  nickel  in  the  mix- 
ture of  the  two  metals  may  now  be  calculated  by  difference. 

It  has  been  assumed  that  lead  and  copper  are  determined  in 
the  process  here  described.  No  essential  modification,  however, 
can  be  made  in  the  method  of  separating  them  from  nickel  and 
cobalt  when  their  determination  is  not  required. 

6.  Modifications  admissible  or  required  for  ores,  or  other  pro- 
ducts of  different  compositions.  • 

If  only  very  little  copper  is  present  (less  than  1  per  cent.),  and 
no  other  metals  of  the  fifth  and  sixth  groups,  the  treatment  of  the 
first  solution  with  H2S  may  be  omitted.  The  copper  then  remains 
in  solution  until  after  the  iron  is  separated  and  is  precipitated 
along  with  nickel  and  cobalt  as  sulphide.  After  the  mixed  sul- 
phides are  dissolved  as  before  described,  the  copper  may  be  sepa- 
rated from  the  slightly  acid  solution  by  hydrogen  sulphide. 

When  no  lead  is  present,  the  treatment  of  the  first  insoluble 
residue  with  ammonium  acetate  is  omitted. 

If  other  metals  of  the  fifth  and  sixth  groups  are  present  no 
modification  is  required.  In  case,  however,  arsenic  is  present  (as 
in  speiss  and  some  ores),  it  is  advisable  to  convert  the  resulting 
arsenic  acid  into  arsenious  by  means  of  sulphurous  acid  before 
treatment  with  H,S. 

No  modifications  are  required  on  account  of  the  presence  of 
any  metals  of  second,  third,  or  fourth  groups,  except  zinc  or  a 


g  215. J  ASSAY    OF    ZIJSTC    ORES.  737 

notable  amount  of  maliganese.  In  respect  to  manganese,  it  can 
safely  be  assumed  when  not  more  than  a  trace  is  present  (as  in 
matte  or  speiss  and  most  ores)  that  the  precipitation  of  nickel  and 
cobalt  as  directed  in  a  solution  containing  a  small  quantity  of  free 
acetic  acid  will  effect  its  separation.  But  if  a  considerable  amount 
is  present  a  small  portion  is  liable  to  be  precipitated  along  with 
the  nickel  and  cobalt  sulphides.  This  can  be  removed  when  the 
mixed  sulphides  are  brought  into  solution,  and  excess  of  acid  is 
removed  by  adding  ammonium  chloride  freely,  also  a  little  ammo- 
nium acetate,  and  repeating  the  precipitation  of  nickel  and  cobalt 
in  same  manner  as  before,  as  sulphides,  taking  care  to  have  the 
solution  always  contain  a  small  quantity  of  free  acetic  acid.  Or 
the  manganese  may  be  separated  from  the  solution  of  the  three 
metals  according  to  £  160,  85,  page  529. 

If  zinc  is  present  it  all  goes  down  with  the  nickel  and  cobalt 
when  they  are  precipitated  as  sulphides.  After  the  mixed  sul- 
phides have  been  dissolved  and  free  acid  has  been  removed  by 
evaporation,  zinc  may  then  be  separated  according  §  160,  75,  p. 
520. 

15.  ASSAY  OF  ZINC  ORES. 
§215. 

Method  of  SCHAFFNER,*  modified  by  C.   KuNZEL,t  as 
employed  in  ttie  Belgian  zinc-works  ;  described  by  C.  GKOLL.^: 

a.  Solution  of  the  ore  and  preparation,  of  the  ammoniacal 
solution,. 

Powder  and  dry  the  ore. 

Take  0'5  grm.  in  the  case  of  rich  ores,  1  grin,  in  the  case  of 
poor  ores,  transfer  to  a  small  flask,  dissolve  in  hydrochloric  acid 
with  addition  of  some  nitric  acid  by  the  aid  of  heat,  expel  the 
excess  of  acid  by  evaporation,  add  some  water,  and  then  excess  of 
ammonia.  Filter  into  a  fceaker,  and  wash  the  residue  with  luke- 
warm water  and  ammonia,  till  ammonium  sulphide  ceases  to  pro- 
duce a  white  turbidity  in  the  washings.  The  oxide  of  zinc 
remaining  in  the  ferric  hydroxide  is  disregarded.  Its  quantity, 


*  Journ.  f.  prakt.  Chem.  73,  410. 

+  Ib.  88,  486.  J  Zeitschr.  f.  anal.  Chem.  1,  21. 


738  SPECIAL    PART.  [§  215. 

according  to  GROLL,  does  not  exceed  0*3 — 0*5  per  cent.  This 
statement  probably  has  reference  only  to  ores  containing  relatively 
little  iron ;  where  much  iron  is  present  the  quantity  of  zinc  left 
behind  in  the  precipitate  may  be  not  inconsiderable.  The  error 
thus  arising  may  be  greatly  diminished  by  dissolving  the  slightly 
washed  iron  precipitate  in  hydrochloric  acid  and  adding  excess  of 
ammonia.  But  the  surer  mode  of  proceeding  is  to  add  to  the 
original  solution — after  evaporating  off  the  greater  part  of  the  free 
acid  as  above,  and  allowing  to  cool — dilute  sodium  carbonate  nearly 
to  neutralization,  then  to  precipitate  the  iron,  after  p.  517,  with 
sodium  acetate,  boiling,  to  filter,  and  wash.  The  washings,  after 
being  concentrated  by  evaporation,  are  added  to  the  filtrate  and 
the  whole  is  then  mixed  with  ammonia,  till  the  first-formed  pre- 
cipitate is  redissolved. 

If  the  ore  contains  manganese — provided  approximate  results 
will  suffice — digest  the  solution  of  the  ore  in  acids,  after  the  addi- 
tion of  excess  of  ammonia  and  water,  at  a  gentle  heat  for  a  long 
time,  and  then  filter  off,  with  the  iron  precipitate,  the  hydrated 
protosesquioxide  of  manganese  which  has  separated  from  the 
action  of  the  air.  The  safer  course — though  undoubtedly  les& 
simple — is,  after  separating  the  iron  with  sodium  acetate,  to  pre- 
cipitate the  manganese  by  passing  chlorine,  as  directed  p.  510,  or 
by  adding  bromine  and  heating. 

If  lead  is  present,  it  is  separated  by  evaporating  the  aqua  regia 
solution  with  sulphuric  acid,  taking  up  the  residue  with  water  and 
filtering ;  then  proceed  as  directed. 

I.  Preparation  and  standardising  of  the  sodium  sulphide 
solution. 

The  solution  of  sodium  sulphide  is  prepared  either  by  dissolving 
crystallized  sodium  sulphide  in  water  (about  100  grm.  to  1000 — 
1200  water),  or  by  supersaturating  a  solution  of  soda,  free  from 
carbonic  acid,  with  hydrogen  sulphide,  and  subsequently  heating 
the  solution  in  a  flask  to  expel  the  excess  of  hydrogen  sulphide. 
Whichever  way  it  is  prepared,  the  solution  is  afterwards  diluted, 
so  that  1  c.c.  may  precipitate  about  O'Ol  grm.  zinc.  Prepare  a 
solution  of  zinc,  by  dissolving  10  grm.  chemically  pure  zinc  in 
hydrochloric  acid,  or  44'122  grm.  dry  crystallized  zinc  sulphate  in 
water,  or  68-133  grm.  dry  crystallized  potassium  zinc  sulphate  in 


§  215.]  ASSAY    OF    ZIXC    ORES.  739 

water,  and  making  the  solution  in  either  case  up  to  1  litre  with 
water. 

Each-c.c.  of  this  solution  corresponds  to  0*01  grm.  zinc.  Now 
measure  off  30 — 50  c.c.  of  this  zinc  solution,  into  a  beaker,  add 
ammonia  till  the  precipitate  is  redissolved,  and  then  400 — 500  c.c.  dis- 
tilled water.  Run  in  sodium  sulphide  as  long  as  a  distinct  precipi- 
tate continues  to  be  formed,  then  stir  briskly,  remove  a  drop  of  the 
fluid  on  the  end  of  a  rod  to  a  porcelain  plate,  spread  it  out  so  that 
it  may  cover  a  somewhat  large  surface,  and  place  in  the  middle  a 
drop  of  pure  dilute  solution  of  nickel  chloride.  If  the  edge  of  the 
drop  of  nickel  solution  remains  blue  or  green,  proceed  with  the 
addition  of  sodium  sulphide,  testing  from  time  to  time,  till  at  last 
a  blackish  gray  coloration  appears  surrounding  the  nickel  solution. 
The  reaction  is  now  completed,  the  whole  of  the  zinc  is  precipi- 
tated, and  a  slight  excess  of  sodium  sulphide  has  been  added.  The 
precise  depth  of  color  of  the  nickel  must  be  observed  and  remem- 
bered, as  it  will  have  to  serve  as  the  stopping  signal  in  future 
experiments.  To  make  sure  that  the  zinc  is  really  quite  precipi- 
tated, you  may  add  a  few  tenths  of  a  c.c.  more  of  the  reagent,  and 
test  again,  of  course  the  color  of  the  nickel-drop  must  be  darker. 
Note  the  number  of  c.c.  used,  and  repeat  the  experiment,  running 
in  at  once  the  necessary  quantity  of  the  reagent,  less  1  c.c.,  and  then 
adding  0*2  c.c.  at  a  time,  till  the  end-reaction  is  reached.  The 
last  experiment  is  considered  the  more  correct  one.  The  sodium 
sulphide  solution  must  be  restandardized  before  each  new  series  of 
analyses. 

c.  Determination  of  the  zinc  in  the  solution  of  the  ore. 

Proceed  in  the  same  way  with  the  ammoniacal  solution  pre- 
pared in  a  as  with  the  known  zinc  solution  in  b.  Here  also  repeat 
the  experiment,  the  second  time  running  in  at  once  the  required 
number  of  c.c.,  less  1,  of  sodium  sulphide,  and  then  adding  0'2  c.c. 
at  a  time,  till  the  end-reaction  makes  its  appearance.  The  second 
result  is  considered  the  true  one.  There  are  three  different  ways 
in  which  this  repetition  of  the  experiment  may  be  made.  You 
may  either  weigh  out  at  the  first  two  portions  of  the  zinc  ore,  or 
you  may  weigh  out  double  the  quantity  required  for  one  experi- 
ment, make  the  ammoniacal  solution  up  to  1  litre  and  employ  i 
litre  for  each  experiment,  or  lastly,  having  reached  the  end-reaction 


740  SPECIAL    PART.  [§  216. 

in  the  first  experiment,  yon  may  add  1  c.c.  of  the  known  zinc  solu- 
tion, which  will  destroy  the  excess  of  sodium  sulphide,  and  then 
run  in  sodium  sulphide  in.  portions  of  O2  c.c.,  till  the  end-reaction 
is  again  attained.  Of  course,  in  this  last  process  to  obtain  the 
second  result,  you  deduct  from  the  whole  quantity  of  sodium  sul- 
phide used  the  amount  of  the  same,  corresponding  to  1  c.c.  of  the 
zinc  solution. 

If  the  ore  contains  copper,  remove  it  from  the  acid  solution  by 
hydrogen  sulphide,  evaporate  the  filtrate  with  nitric  acid,  dilute, 
treat  with  ammonia,  and  determine  the  zinc  as  above. 


[16.  PAETIAL  ANALYSIS   OF  IKON   OEES. 


For  the  purpose  of  ascertaining  the  quantity  and  more  especially 
the  quality  of  the  iron,  which,  can  be  produced  from  an  ore,  deter- 
minations of  iron,  phosphorus,  sulphur,  and  manganese,  without 
regard  to  other  constituents,  are  often  required.  An  examination 
of  the  ore  for  titanic  acid,  especially  if  it  is  a  magnetic  iron  ore,  is 
also  often  demanded.  Frequently  a  determination  of  only  two  or 
three  of  these  substances,  as  iron  and  phosphorus,  or  phosphorus 
and  sulphur,  is  required.  In  any  case  it  is  most  convenient  to  use 
a  separate  portion  of  the  ore  for  the  determination  of  each  sub- 
stance. 

» 

-v. 

IKON. 

Iron  may  be  determined  volumetrically  many  ways.  For  the 
present  purpose,  either  of  the  two  following  methods  may  be 
used. 

1.  Decompose  2  grm.  with  concentrated  hydrochloric  acid  by 
heating  gently  on  a  sand-bath  in  a  covered  beaker,  having  a  capac- 
ity of  not  less  than  half  a  litre.  If  the  ore  contains  carbonaceous 
matter,  the  weighed  portion  should  first  be  ignited  with  exposure 
to  the  air  until  the  carbon  is  burned  out.  Two  or  three  hours 
suffice  for  the  decomposition  of  most  limonites  and  magnetites,  but 
some  varieties  of  hematite  resist  the  action  of  acid  for  a  long  time. 
The  appearance  of  the  still  undissolved  residue,  which  may  consist 
of  quartz,  clay,  hornblende,  or  other  silicates,  will  indicate  when  the 


§216.]  PARTIAL    ANALYSIS    OF    IKON    ORES.  741 

oxide  (or  carbonate)  of  iron  in  the  ore  is  dissolved.*  Dilute  some- 
what and  filter,  add  to  the  filtrate  20  to  30  c.c.  of  strong  sulphuric 
acid,  or  an  equivalent  amount  of  dilute,  and  evaporate  till  hydro- 
chloric acid  is  all  removed,  avoiding  a  heat  much  above  100°  C. 
After  cooling,  add  about  100  c.c.  of  water  and  digest  till  the  ferric 
sulphate  has  gone  into  solution.  Then  pour  the  solution  into  a 
half-litre  flask,  without  filtering  from  a  slight  residue  of  silica 
which  may  have  separated,  dilute  up  to  the  mark,  mix  thoroughly, 
and  make  two  determinations  of  iron,  each  in  100  c.c.  of  this  solu- 
tion, by  reduction  to  ferrous  sulphate  and  titration  with  potassium 
permanganate  according  to  §  113,  3,  #,  p,  278. 

2.  Proceed  as  above  until  the  decomposition  with  hydrochloric 
acid  has  been  effected.  Now,  if  noferr&its  iron  is  present,  concen- 
trate, if  the  volume  of  the  liquid  is  greater,  to  20 — 30  e.c.  and  dilute 
without  filtering  in  a  half-litre  flask  to  500  c.c,,  and  determine  iron 
in  portions  of  100  c.c.  each,  according  to  113,  3,  1>  (titration  with 
standard  sodium  thiosulphate  and  iodine  solutions).  If  ferrous  iron 
is  present,  add,  a  little  at  a  time,  potassium  chlorate  (less  than  f  gr. 
for  2  grm.  ore  usually  suffices)  until  a  minute  portion  of  the 'solution 
taken  out  writh  pointed  glass  rod  and  tested  after  dilution  on  a 
watch-glass  with  fresh  solution  of  potassium  ferricyanide  gives  no 
blue  color.  The  unavoidable  excess  of  potassium  chlorate  must 
now  be  decomposed  by  heating  with  hydrochloric  acid,  and  the 
liberated  chlorine  removed  by  evaporating  off  about  half  the  solu- 
tion. Next  dilute  to  500  c..c.  and  determine  the  iron  by  the  process 
just  mentioned. 

PHOSPHORUS. 

Take  5  grm.  of  the  ore,  unless  it  is  known  to  contain  a  rather 
large  quantity  of  phosphoric  acicl,  in  which  case  2  or  3  grm.  should 
be  used.  Decompose  with  concentrated  hydrochloric  acid  in  a 
beaker  having  a  diameter  at  the  bottom  of  about  9  centimetres. 
The  solution,  without  filtering  from  the  insoluble  residue,  may  be 
allowed  to  evaporate  in  a  sand-bath  nearly  to  dry  ness,  but  before 
the  liquid  has  been  all  removed,  transfer  the  beaker  to  an  air- 

*  Some  iron  ores,  especially  magnetites,  contain  a  small  quantity  of  iron  exist- 
ing as  a  constituent  of  a  silicate  (e.g..  hornblende  or  garnet),  undecomposable 
by  hydrochloric  acid.  In  the  assay  of  iron  ores,  the  slight  inaccuracy  which 
on  this  account  results  is  usually  disregarded. 


742  SPECIAL   PART.  ["§  216. 

bath*  provided  with  a  thermometer,  and  continue  the  evaporation 
at  a  temperature  of  130°  to  140°  C.  until  the  mass  is  quite  dry  and 
appears  no  longer  sticky,  but  brittle  when  touched  with  a  glass  rod. 
Then,  after  cooling,  add  concentrated  nitric  acid  (40  to  50  c.c.)  and 
heat  on  a  sand-bath  until  the  iron  is  again  dissolved  and  only  a 
residue  similar  in  color  and  appearance  to  the  original  insoluble 
residue  remains.  This  solution  of  the  iron  in  nitric  acid  is  easily 
effected,  provided  the  heat  used  in  the  preceding  drying  operation 
has  not  exceeded  the  prescribed  limit.  The  excess  of  nitric  acid, 
however,  which  it  is  usually  necessary  to  use  for  this  purpose,  if 
allowed  to  remain  in  the  free  state,  retards  the  subsequent  precipi- 
tation of  phosphoric  acid  by  molybdic  acid  solution,  and  may  even 
cause  an  appreciable  error  by  retaining  a  portion  permanently  in 
solution.  Evaporate  off,  therefore,  a  part  of  the  nitric  acid,  reduc- 
ing the  volume  to  about  25  c.c.  If  the  evaporation  proceeds  too 
far,  basic  ferric  salts  containing  phosphoric  acid  will  remain  undis- 
solved  on  subsequent  addition  of  water.  After  proper  concentra- 
tion, add  100  c.c.  of  cold  water,  stir,  and  allow  the  insoluble  residue, 
which  must  not  show  evidence  of  containing  basic  ferric  salts,  to 
settle.  Filter  into  a  tall  narrow  beaker,  or  better  still  into  a  cone- 
shaped  flask.  To  the  filtrate  and  washings,  which  need  hardly 
exceed  200  c.c.,  add  100  c.c.  of  molybdic  acid  solution  (prepared  as 
directed  in  "Qual.  Anal.,"  p.  72).  Add  next  gradually  ammonia 
so  long  as  the  reddish-brown  precipitate,  which  it  forms,  dissolves 
very  readily  on  stirring.  A  few  cubic  centimetres  can  usually  be 
added  at  this  point,  without  danger  of  forming  a  permanent  iron 
precipitate,  on  account  of  the  free  nitric  acid  which  the  added 
molybdic  acid  solution  contained.  Stir  well  the  solution,  which 
should  now  occupy  a  volume  of  300  to  350  c.c.,  and  let  it  stand  at 
a  temperature  of  40°  to  50°  C.  at  least  24  hours.  The  greater  part 
of  the  solution  standing  over  the  precipitated  ammonium  phos- 
phomolybdate  can  be  removed  perfectly  clear  by  means  of  a  siphon. 

*  A  suitable  air-bath  may  be  easily  constructed  as  follows :  Procure  an  iron 
pot  having  its  diameter  greatest  at  the  rim  (about  12  inches),  fit  a  sheet  tin  cover 
to  it,  cut  circular  holes  (2  or  4)  in  the  cover  10  centimetres  in  diameter  to  receive 
the  beaker  (which  must  be  selected  of  a  proper  size),  and  also  a  small  hole  in  the 
centre  for  inserting  a  thermometer.  The  pot  is  heated  by  setting  it  into  a  sheet- 
iron  cylinder,  made  to  fit  it,  down  to  the  rim,  and  placing  a  Bunsen  burner  under 
it  within  the  cylinder. 


§  216.]  PARTIAL   ANALYSIS    OF   IKON    ORES.  74:? 

Collect  the  precipitate  on  a  small  filter  (2-J  inches  in  diameter) 
and  wash  it  with  the  same  molybdic  acid  solution  that  is  used  for 
precipitation,  diluted  with  an  equal  volume  of  water.  Allow  the 
filtrate  and  washings  to  stand  in  a  warm  place  several  hours  to 
-ascertain  whether  any  more  phosphoric  acid  can  be  precipitated. 
The  moist  precipitate  is  to  be  dissolved  on  the  filter  with  ammonia. 
It  is  advisable  to  have  the  ammonia  used  for  this  purpose  in  a 
.small  graduated  glass  cylinder  so  that  the  quantity  used  may  be 
observed.  Pour  2  or  3  c.c.  into  the  flask  in  which  the  precipita- 
tion has  been  effected  in  order  to  dissolve  what  may  adhere  to  it, 
then  pour  from  the  flask  upon  the  filter,  and  at  the  same  time  stir 
up  the  precipitate  with  a  jet  of  hot  water.  Repeat  this  operation 
till  complete  solution  takes  place.  By  cautious  use  of  ammonia 
solution  (sp.  gr.  -95)  its  volume  should  be  restricted  to  about  10  c.c. 
for  small  quantities  of  the  precipitated  phosphomolybdate,  while 
for  comparatively  large  quantities,  such  as  are  obtained  from  4  gr. 
of  ore  containing  upwards  of  '5  per  cent,  of  phosphoric  acid,  more 
may  be  used.  Usually  the  solution,  after  passing  through  the  fil- 
ter remains  clear  or  at  most  exhibits  but  a  slight  opalescence.  Occa- 
sionally it  is  turbid  to  such  extent  that  it  is  advisable  to  pass  it 
through  the  same  filter  again.  Wash  the  solution  out  of  the  filter 
paper  with  the  smallest  sufficient  volume  of  hot  water.  Add  now, 
according  to  the  quantity  of  the  dissolved  precipitate,  6  to  12  c.c. 
of  hydrochloric  acid  (sp.  gr.  1-1).  If  this  occasions  (by  super- 
saturation  of  the  ammonia)  a  permanent  precipitate  of  ammonium 
phosphomolybdate,  redissolve  it  with  a  slight  excess  of  ammonia, 
adding  enough  to  give  a  perceptible  odor  of  ammonia  to  the  solu- 
tion when  'cold.  This  addition  of  a  measured  volume  of  hydro- 
chloric acid  is  designed  to  form  a  moderate  quantity  of  ammonium 
chloride — not  enough  to  have  a  sensible  solvent  effect  on  the 
ammonium  magnesium  phosphate  which  is  next  to  be  precipitated, 
but  sufficient  to  prevent  the  coprecipitation  of  other  magnesium 
compounds.  Xext  precipitate  the  phosphoric  acid  with  "mag- 
nesium mixture"  (see  p.  113).  An  excess  of  this  solution  is 
required  to  effect  complete  precipitation  of  phosphoric  acid ;  8  to 
10  c.c.  may  be  used  in  any  case,  while  more  may  be  required  if 
the  ore  is  rich  in  phosphoric  acid.  Finally,  to  render  the  separa- 
tion of  ammonium  magnesium  phosphate  complete,  add  to  the 
solution  about  one-tenth  its  volume  of  ammonia  solution,  and  stir 


744  SPECIAL    PART.  [§  216. 

well.  The  preceding  operations  should  be  conducted  in  such  a 
manner  as  not  to  unnecessarily  increase  the  volume  of  the  solution. 
The  iinal  volume  after  addition  of  all  reagents  may  amount  to  40 
to  60  c.c.  in  ordinary  cases,  or  to  100  c.c.  for  ores  containing  an 
unusually  large  quantity  of  phosphorus.  Filter  the  solution  after 
standing  6  to  12  hours  in  the  cold,  wash  the  precipitate  with  dilute 
ammonia,  dry,  detach  from  the  filter  (unless  the  quantity  is  very 
small),  incinerate  the  filter  in  an  open  platinum  crucible,  add  the 
precipitate,  ignite,  weigh,  and  calculate  the  amount  of  phosphorus 
(or  if  required  P2Of))  in  the  ore. 

In  view  of  the  importance  of  accurate  determinations  of  phos- 
phorus in  iron  ores,  pig-iron,  &c.,  for  technical  purposes,  some 
further  explanation  may  here  be  properly  given  of  the  causes  of 
the  possible  errors  which  the  above  directions  are  intended  to- 
obviate.  If,  in  the  beginning  of  the  process,  HC1  is  not  removed 
by  evaporation  to  dryness,  it  may  prevent  complete  precipitation  of 
phosphoric  acid  by  the  molybdic  acid  solution/"  The  presence  of 
a  large  quantity  of  free  nitric  acid  also  prevents  precipitation  of 
the  last  traces  of  phosphoric  acid  by  the  molybdic  solution.  If,  in 
attempting  to  obviate  this  cause  of  error  by  evaporating  the  nitric 
acid,  the  evaporation  is  carried  too  far,  basic  ferric  nitrate  will 
be  formed,  which  will  retain1  phosphoric  acid.  If  too  great  heat 
is  used  in  precipitating  the  ammonium  phosphomolybdate,  free 
molybdic  acid  will  be  deposited  along  with  it.  A  slight  deposition 
of  molybdic  acid,  provided  the  precipitate  remains  pulverulent, 
may  have  no  sensible  injurious  effect ;  but  a  larger  amount,  espe- 
cially if  deposited  in  the  form  of  a  crust,  will  retain  iron  which 
cannot  be  washed  out  on  the  filter.  If  then  ammonia  is  applied 
to  dissolve  the  precipitate  on  the  filter,  a  ferric  compound  contain- 
ing phosphoric  acid  will  remain  on  the  filter  undissolved. 

In  order  to  insure  the  complete  precipitation  of  phosphoric 
acid,  it  is  necessary  to  use  not  only  enough  molybdic  solution  to 


*  It  is  true  that  after  evaporation  and  drying  at  a  temperature  between  130° 
and  140°  C.  some  chlorine,  still  remains  as  ferric  chloride,  wh ich  might  be  further 
decreased  or  entirely  removed  by  evaporating  again  the  nitric  acid  solution  to- 
dryness.  I  have  repeatedly  taken  this  course  and  compared  the  results  with 
those  obtained  without  evaporating  a  second  time ;  but  do  not  thereby  obtain  a 
larger  amount  of  phosphorus,  and  conclude  that  this  extra  precaution  is  unnec- 
essarv. — O.  D.  A. 


£  216.]  PARTIAL   ANALYSIS   OF   IRON    ORES.  745 

convert  it  into  ammonium  phosphomolybdate,  but  a  liberal  excess 
proportional  to  the  volume  of  the  solution.  It  may  occasionally  hap- 
pen, in  case  of  an  ore  or  a  sample  of  iron  unexpectedly  rich  in 
phosphorus,  that  100  c.c.  will  not  suffice.  But  since  more  inolybdic 
solution  is  added  in  the  process  of  washing  the  precipitate,  the 
formation  of  an  additional  precipitate  in  the  filtrate,  which  should 
l)e  kept  warm  f>  hours,  will  indicate  any  deficiency  in  the  quantity 
of  rnolybdic  solution  first  used. 

If,  in  the  final  precipitation  as  ammonium  magnesium  phos- 
phate, a  large  amount  of  free  ammonia,  and  no  ammonium  chloride, 
is  present  when  the  magnesia  mixture  is  added,  it  is  possible  that 
magnesium  oxide  or  basic  magnesium  phosphate  may  be  coprecipi- 
tated ;  while,  on  the  other  hand,  a  very  large  amount  of  ammonium 
chloride  may  retard  the  precipitation  of  phosphoric  acid.  If  the 
precipitation  is  attempted  in  too  large  a  volume  of  solution  there 
is  more  danger  that  it  may  not  be  complete,  and  also  more  diffi- 
culty in  removing  the  precipitate  from  the  sides  of  the  vessel,  to 
which  it  may  adhere  in  the  form  of  minute  transparent  crystals. 

Finally,  notwithstanding  the  use  of  all  due  precaution,  the 
weighed  magnesium  pyrophosphate  may  contain  a  trace  of  silica 
— so  slight  that  it  may  in  most  cases  be  neglected.  But  if  a  very 
accurate  determination  of  minute  quantities  of  phosphorus  in  the 
purer  kinds  of  ore,  iron,  &c.,  is  required,  it  is  advisable  to  dissolve 
the  weighed  precipitate  in  the  crucible  by  warming  with  nitric  or 
hydrochloric  acid,  collect  any  remaining  residue  on  a  very  small 
filter,  wash,  return  to  the  crucible,  ignite,  weigh,  and  deduct  the 
weight  of  the  crucible  +  silica  from  its  weight  +  first  ignited 
pyrophosphate. 

Sulphur.  If  any  considerable  quantity  of  metallic  sulphides 
is  visible  on  close  inspection  of  the  ore,  take  5  grm.  finely  pul- 
verized. If  no  sulphides  can  be  seen  take  7  to  10  grin.  Add  to 
the  ore  in  a  large  beaker  about  20  c.  c.  of  aqua  regia  for  each 
gramme  taken.  Allow  it  to  stand  at  common  temperature  of  the 
room  6  hours,  then  12  hours  longer  at  40°  to  50°  C.  Finally 
evaporate  to  dryness,  treat  the  residue  with  strong  hydrochloric 
acid,  dilute  to  200  to  300  c.c.,  filter,  concentrate  to  about  100  c.c.,, 
transfer  to  a  small  beaker,  add  while  hot  a  few  c.c.  of  barium 
chloride  solution.  If  the  ore  contains  much  sulphur,  the  greater 
part  of  the  sulphuric  acid  produced  from  it  will  be  at  once  precipi- 


746  SPECIAL    PART.  .[§  216. 

tated ;  a  quantity  far  too  great  to  neglect,  however,  will  remain  in 
solution  on  account  of  the  presence  of  free  acids  and  ferric  salts. 
If  the  ore  contains  a  comparatively  small  though  still  determinable 
amount  of  sulphur,  it  may  happen  that  no  precipitate  will  appear 
at  this  stage.  In  either  case,  therefore,  remove  the  free  acid  by 
evaporation,  after  the  addition  of  barium  chloride  so  far  as  it  can 
be  removed  without  the  formation  of  basic  ferric  salts  insoluble  in 
water.  The  last  part  of  the  evaporation  is  carried  on  best  by  heat- 
ing the  small  beaker  in  an  iron  plate.  The  solution  may  usually 
be  brought  thus  to  a  volume  of  10  or  15  c.c.  The  formation  of  a 
xlark  pellicle  on  the  surface  of  the  liquid  at  this  stage  can  usually 
be  observed,  and  is  a  sure  indication  that  further  evaporation 
would  render  the  iron  insoluble  in  water.  After  cooling,  add 
cold  water  (about  100  c.c.)  and  1  c.c.  dilute  HC1  to  dissolve  the 
soluble  saline  matter.  If  the  ore  contained  sulphur,  a  residue  of 
barium  sulphate  will  now  appear.*  (If  the  preceding  evaporation 
has  been  carried  too  far  a  bulky  mass  of  ferric  salts  will  remain 
undissolved,  in  which  case  add  hydrochloric  acid  freely  till  it  dis- 
solves, and  repeat  the  evaporation.)  The  barium  sulphate  thus 
obtained  usually  contains  iron  and  other  impurities.  Collect  it  on 
a  filter,  wash  till  the  greater  part  of  the  saline  matter  is  removed, 
ignite  in  an  open  platinum  crucible  till  carbon  is  burned  away, 
add  a  little  sodium  carbonate,  fuse,  warm  the  fused  mass  with 
water  in  the  crucible  until  it  becomes  disintegrated ;  pour  the 
contents  upon  a  small  filter,  wash  the  sodium  sulphate  out  of  the 
insoluble  part,  add  IIC1  to  the  filtrate  till  it  gives,  after  boiling,  an 
acid  reaction  with  test  paper  (avoiding  much  excess  of  acid),  and 
precipitate  wrhile  boiling  with  barium  chloride.  The  barium  sul- 
phate thus  obtained,  after  washing  first  by  decantation  2  or  3  times, 
and  afterwards  011  a  filter  with  boiling  water,  may  be  assumed  to 
be  sufficiently  pure.  "Weigh  it  and  calculate  percentage  of  sulphur 
in  the  ore. 


*  The  nitric  and  hydrochloric  acids  used  for  the  examination  must  always 
be  tested  for  sulphuric  acid  as  follows:  Evaporate  200  c.c.  (or  the  same  volume 
used  in  analysis)  of  the  mixed  acids,  with  addition  of  a  few  centigrammes  of 
pure  Na2CO3  till  only  some  half  dozen  drops  remain,  dilute,  add  barium 
chloride  while  hot.  If  a  weighable  amount  of  BaSO4  is  formed,  weigh  it.  If 
the  weight  of  BaSO4  from  the  200  c.c.  does  not  exceed  '002  or  -003  gr.,  the  acids 
may  be  used  with  the  required  correction  of  result. 


£  216.]  PARTIAL   ANALYSIS    OF    IKON    ORES.  747 

MANGANK*K. 

1.  Method  suitable  for  ores  not  t/n  usually  rich  in  manganese. 

The  most  reliable  methods  of  determining  manganese  in  iron 
ores  involve  the  precipitation  of  iron  as  basic  ferric  acetate.  In 
order  to  avoid  the  tedious  operation  of  washing  a  large  quantity  of 
iron  precipitated  in  this  form,  the  whole  volume  of  the  solution  in 
which  the  precipitate  is  formed  may  be  measured,  and  after  the 
precipitate  has  settled  a  measured  portion  of  the  nearly  clear 
supernatant  liquid  may  be  taken  for  the  determination  of  man- 
ganese. A  wide  graduated  cylinder  of  thin  glass  holding  1200  to 
1400  c.c.  is  required  for  measuring  the  solution.*  Take  4  or  5  grm. 
ore,  decompose  with  strong  hydrochloric  acid,  evaporate  to  dryness 
(with  addition  of  nitric  acid  if  ferrous  iron  is  present),  redissolve 
with  strong  hydrochloric  acid,  evaporate  off  the  greater  part  of  the 
excess  of  acid  used  for  redissolving,  dilute  and  filter  into  a  flask 
capable  of  holding  at  least  1500  c.c.,  previously  marked  at  a  height 
corresponding  to  1000  c.c. 

Precipitate  now  the  iron  by  the  successive  addition  of  sodium 
carbonate,  a  little  hycrochloric  acid,  acetic  acid,  sodium  acetate,  and 
boiling;  according  to  directions  given  in  §  160,  71.  The  final  vol- 
ume to  which  the  solution  is  brought  before  boiling  must  in  this 
case  be  limited  to  about  1000  c.c.  After  precipitation,  pour  the 
contents  of  the  flask  immediately  without  cooling  into  the  gradu- 
ated vessel,  rinse  the  flask  with  a  small  volume  of  water  which 
must  be  carefully  mixed  from  top  to  bottom  with  the  main  solu- 
tion by  stirring  with  a  long  glass  rod.  When  the  precipitate  has 
settled  to  such  an  extent  that  at  least  half  of  the  solution  can  be 
drawn  off  nearly  free  from  suspended  matter,  note  the  volume 
which  it  occupies,  and  siphon  off  the  nearly  clear  solution.  Note 
the  volume  remaining.  Suppose,  having  used  5  gr.  ore,  the  whole 
volume  was  1140  c.c.,  and  the  remaining  volume  420  c.c.  The 


*  If  a  suitable  measuring  vessel  is  not  at  hand,  one  which  will  suffice  may  be 
prepared  in  the  following  manner :  Procure  a  tall  narrow  beaker  (9 — 10  in.  in 
height,  3 — 3|  in.  in  diameter).  Run  50  c.c.  of  water  into  it  from  a  burette;  mark 
the  side  of  the  beaker  at  the  surface  of  the  liquid  with  a  writing  diamond  (or 
mark  with  a  pencil  a  vertical  strip  of  paper  fastened  to  the  beaker  with  shellac). 
Continue  adding  portions  of  50  c.c.  and  marking  till  the  vessel  is  filled.  After- 
wards graduate  the  portion  between  1000 c.c. and  1200  c.c.,  also  between  300  c.c. 
and  500  c.c.,  into  spaces  corresponding  each  to  10  c.c. 


748  SPECIAL    PART.  [§  216. 

volume  drawn  off  is  then  1140  —  420  =  720  c.c.,  corresponding  to 

720 

— - —  x  5  gr.  ore  ;  or  rather  the  720  c.c.  corresponds  approximately 

to  that  amount  of  ore.  For  no  account  is  taken  of  the  volume 
occupied  by  the  solid  ferric  acetate,  nor  can  very  accurate  measure- 
ments be  made  in  wide  graduated  glass  vessels.  But  these  sources 
of  error  have  no  appreciable  influence  on  the  final  result  unless  the 
ore  is  comparatively  rich  in  manganese  (containing  over  2  or  3  per 
cent.).  For  such  ores  it  is,  in  fact,  preferable  to  use  1  grm.  for  the 
determination,  and  wash  the  basic  ferric  acetate  in  the  ordinary 
manner. 

The  solution  which  is  drawn  off  by  means  of  a  siphon  may  con- 
tain, besides  a  little  suspended  iron  precipitate,  a  trace  of  iron  still 
in  solution,  calcium  and  magnesium,  and  a  large  amount  of  saline 
matter.  Concentrate  without  filtration  by  evaporation  in  a  beaker, 
or,  more  expeditiously.  by  boiling  in  a  flask  to  about  300  c.c. ; 
add  sodium  carbonate  to  alkaline  reaction,  boil  and  add  a  little 
sodium  hydroxide.  Manganese  is  thus  precipitated  along  with 
iron  calcium,  &c. ;  collect  the  precipitate  on  a  filter,  wash  slightly 
and  dissolve  on  the  filter  with  the  smallest  possible  quantity  of 
hydrochloric  acid.  If  the  precipitate  dissolves  with  difficulty  on 
account  of  the  presence  of  higher  oxides  of  manganese,  add  a  few 
drops  of  solution  of  sulphurous  acid.  Boil  the  filtrate  to  expel 
chlorine,  or  if  sulphurous  acid  has  been  used,  boil  with  addition  of 
a  few  drops  of  nitric  acid.  Add  sodium  carbonate  solution  till  a 
slight  deepening  of  color,  due  to  presence  of  ferric  chloride,  indi- 
cates that  the  solution  is  nearly  neutral.  (If  sufficient  iron  is  not 
already  present  to  give  this  indication,  two  or  three  drops  of  ferric 
chloride  solution  may  be  added.)  Add  next  sodium  acetate  and 
boil  to  precipitate  the  slight  quantit}'  of  iron  present,  and  filter  the 
hot  solution.  If  the  preceding  operations  have  been  properly  con- 
ducted, the  filtrate  and  washings  need  rarely  exceed  200  c.c.  Pre- 
cipitate the  manganese  in  it  by  adding  aqueous  solution  of  bromine 
and  keeping  it  warm  a  few  hours.  When  the  excess  of  bromine 
has  escaped,  filter  and  wash  with  hot  water.  Test  the  filtrate  for 
manganese  by  adding  a  little  more  bromine  solution  and  also  more 
sodium  acetate.  Ignite  the  precipitate  and  weigh  as  Mn3O4.  The 
manganese  protosesquioxide  thus  obtained  may  contain  a  trace  of 
soda ;  but  when  the  quantity  does  not  amount  to  more  than  2  or  % 


§216.]  PARTIAL    ANALYSIS    OF    JliOX    ORES.  749 

per  cent,  of  the  ore,  it  is  not  probable  that  greater  accuracy  would 
be  attained  by  dissolving  it  and  converting  the  manganese  into 
another  form  for  weighing.  But  it  should,  after  weighing,  be 
examined  to  ascertain  whether  it  contains  enough  cobalt  to  cause 
an  appreciable  error  in  the  estimation  of  manganese,  since  traces  of 
cobalt  are  frequently  present  in  iron  ores,  more  especially  in  brown 
hematites.  Dissolve  it  in  hydrochloric  acid,  evaporate  to  a  few 
drops.  If  the  bright  green  color,  which  even  a  very  small  amount 
of  cobalt  would  occasion,  does  not  appear,  it  may  be  assumed  that 
cobalt  is  not  present  in  sufficient  quantity  to  require  any  change  in 
the  percentage  of  manganese  calculated  from  the  weighed  pro- 
tosesquioxide.  But  if  the  color  indicates  presence  of  cobalt,  con- 
tinue the  evaporation  with  heat  not  exceeding  100°  C.  until  free 
acid  is  completely  removed.  Dissolve  the  residue  in  about  20  c.c. 
of  water  and  acidify  with  not  more  than  one  or  two  drops  of  acetic- 
acid,  add  sodium  acetate,  heat  and  pass  H2S  through  the  solution. 
Cobalt  will  then  be  precipitated  as  sulpide.  If  the  quantity  is 
sufficient,  the  cobalt  may  be  determined  by  converting  it  into 
cobalt  sulphate  (see  p.  -265);  or  manganese  may  be  determined  in 
the  filtrate  from  the  cobalt  sulphide,  by  precipitating  (after  boiling 
out  H2S)  with  sodium  carbonate,  igniting  and  weighing  again  as 
Mn,0, 


2.  Method  suitable  for  Ores  containing  larger  yminttfit-x  <>f 
Manganese. 

Weigh  out  from  '75  to  1*  gr.  and  proceed  as  in  the  above- 
described  process  so  far  as  the  precipitation  of  iron  as  basic  ferric 
acetate.  Filter,  wash  the  precipitate  (best  collected  on  two  filters) 
with  hot  water  containing  1  or  2  per  cent,  of  sodium  acetate.  Boil 
the  filtrate  and  washings,  and  filter  again  if  any  additional  flocks  of 
basic  ferric  acetate  separate.  Concentrate  the  filtrate  to  600  —  800 
c.c,,  transfer  about  one-half  of  the  solution  into  another  beaker, 
nearly  or  quite  neutralize  the  acetic  acid  which  it  contains  with 
sodium  carbonate,  add  to  it  the  remainder  of  the  solution  which 
still  contains  free  acid,  and  should  dissolve  any  slight  precipitate 
caused  by  sodium  carbonate.  Precipitate  next  manganese  with 
hromine  and  treat  the  precipitate  as  above  directed  in  1,  not  omit- 
ting examination  for  cobalt  ;  or,  if  great  accuracy  is  desired,  the 
manganese  may  be  converted  into  pyrophosphate  for  weighing. 


750  SPECIAL    PART.  [ 

TITANIC  ACID. 

Qualitative  examination.  Fuse  about  1  grm.  of  \hQJvtiely  pul- 
verized ore  with  potassium  disulphate  in  the  manner  described 
below  under  "  Quantitative  determination."  Treat  the  fused  mass 
with  boiling  dilute  hydrochloric  acid,  which  readily  dissolves  the 
iron  and  titanic  acid.  Boil  the  solution,  without  filtering  from  the 
insoluble  residue  which  usually  remains,  in  a  porcelain  casserole 
with  granulated  tin.  If  the  violet  color  indicating  titanium  does 
not  sooner  appear,  concentrate  by  rapid  boiling,  with  addition  of 
more  tin  in  case  the  first  portion  has  dissolved,  until  saline  matter 
begins  to  be  deposited  and  but  some  half-dozen  c.  c.  of  liquid 
remain.  If  no  decided  violet  color  now  appears  it  may  be  con- 
cluded that  either  no  titanium  or  but  very  little  is  present.  The 
only  certain  way  to  detect  minute  quantities  is  to  proceed  as  in 
quantitative  determinations,  which  indeed  requires  but  little  more 
time  if  the  method  of  decomposing  the  ore  with  hydrofluoric  acid 
is  employed. 

Quantitative  determination.  Fuse  1  grm.  of  the  very  finely 
pulverized  ore  with  potassium  disulphate.  The  potassium  disul- 
pliate  has  but  little  effect  on  the  ore  until  the  temperature 
approaches  dull  redness.  If  it  contains  too  much  sulphuric  acid 
it  will  froth  and  occasion  mechanical  loss  before  the  proper  tem- 
perature is  reached.  If  prepared  strictly  according  to  directions  in 
g  64,  7,  p.  115,  this  trouble  will  be  obviated.  After  the  bottom  of 
the  crucible  is  faint  red,  apply  no  more  heat  than  is  just  sufficient 
to  maintain  the  mass  in  a  state  of  fusion.  The  temperature  must 
be  gradually  increased,  since  the  sulphate  becomes  more  and  more 
infusible  as  fumes  of  sulphuric  acid  escape  with  formation  of  nor- 
mal sulphate.  When  the  mass  is  no  longer  fluid  at  a  full  red  heat, 
allow  it  to  cool ;  add  concentrated  sulphuric  acid  (2  or  3  c.  c.),  heat 
very  gradually  until,  aided  by  stirring  with  a  platinum  wire,  the 
fused  mass  becomes  disintegrated  and  mixed  with  the  acid.  The 
temperature  may  then  be  gradually  increased  as  before. 

The  progress  of  the  decomposition  may  be  ascertained  by  dip- 
ping a  thick  cold  platinum  wire  or  spatula  to  the  bottom  of  the 
crucible,  allowing  it  to  cool  and  repeating  the  dipping  a  few  times. 
By  inspection  of  the  sample  thus  taken  up  with  a  lens  one  can  see 
whether  undecomposed  particles  of  magnetite  are  present.  One 
addition  of  fresh  sulphuric  acid  often  suffices,  but  the  addition  of 


£216.]  PARTIAL   ANALYSIS    OF   IRON   ORES.  751 

acid  and  reheating  may  be  repeated  as  often  as  required.  It  is 
advisable  at  the  end  of  the  operation,  after  the  decomposition 
appears  complete,  to  incorporate  a  liberal  amount  of  sulphuric  acid 
uniformly  with  the  mass,  and  allow  the  greater  part  to  remain  in 
order  to  facilitate  subsequent  solution  of  the  mass  in  water.  After 
cooling,  digest  with  300  c.  c.  of  cold  water  until  all  soluble  matter 
(ferric  sulphate,  titanic  acid)  is  taken  up.  This  often  requires  a 
long  time,  usually  24  to  48  hours.  If  the  ore  contains  quartz  or 
silicates  an  insoluble  residue  is  sure  to  remain,  possibly  retaining  a 
small  quantity  of  titanic  acid.  Collect  it  on  a  filter,  incinerate  the 
filter,  and  fuse  the  residue  with  a  small  quantity  of  potassium 
disulphate,  and  at  the  end  of  the  operation  add>  after  the  mass  has 
sufficiently  cooled,  concentrated  sulphuric  acid  enough  to  retain 
the  potassium  salt  and  the  titanic  acid  permanently  in  solution. 
Heat  till  the  whole  is  liquid  with  exception  of  the  undecomposable 
parts  of  the  ore,  cool,  and  put  the  crucible  with  its  still  liquid  con- 
tents into  a  small  beaker  containing  just  sufficient  water  to  cover 
it.  If  titanic  is  present  it  will  now  readily  go  into  solution.  The 
filtered  solution  can  be  treated  for  titanic  separately  like  the  main 
solution,  or  it  may  be  added  to  the  main  solution.  To  separate 
titanic  acid  from  the  first  solution,  or  from  the  two  mixed  solu- 
tions, add  first  sodium  carbonate  so  long  as  it  can  be  added  without 
producing  a  permanent  precipitate,  then  3  c.  c.  of  pure  dilute  sul- 
phuric acid  and  100  to  150  c.  c.  strong  solution  of  sulphurous  acid ; 
expose  to  heat  of  40°  to  50°  C.  an  hour.  If  the  solution  continues 
to  smell  of  sulphurous  acid  enough  of  that  reagent  has  been  added, 
otherwise  more  should  be  added.  Dilute  to  TOO  to  800  c.  c.  in  a 
large  beaker  and  boil  steadily  2  hours,  covered  with  a  watch-glass* 
A  moderate  quantity  of  free  acid  must  be  present  to  prevent  iron 
from  being  precipitated.  The  iron  must  aiso  be  in  the  state  of 
ferrous  sulphate.  Too  much  free  acid  prevents  precipitation  of 
titanic  acid.  When  a  considerable  amount  of  titanic  acid  is  present 
the  formation  of  a  precipitate  on  heating  the  solution,  a  little 
before  the  actual  boiling  begins,  is  an  indication  that  the  free  acid 
present  does  not  exceed  the  proper  amount.  -  To  compensate  for 
the  water  lost  by  evaporation  during  the  boiling,  add  from  time  to 
time  hot  water  so  gradually  as  not  to  check  the  boiling.  A  little 
solution  of  sulphurous  acid  should  be  mixed  with  the  water  thus, 
added  to  keep  the  iron  in  the  state  of  ferrous  sulphate. 


752  SPECIAL    PART.  [§216. 

Allow  the  precipitated  titanic  acid  to  settle  till  the  solution 
above  it  is  perfectly  clear  (12  to  24  hours).  Filter  (not  with  a 
Bunsen  pump)  through  a  filter  carefully  fitted  to  the  funnel  and 
stir  the  precipitate  as  little  as  possible  during  the  washing,  as  it  is 
somewhat  inclined  to  pass  through  the  pores  of  the  filter  paper ;  if 
necessary,  ammonium  sulphate  may  be  added  to  the  water  used  for 
washing  to  prevent  this  tendency,  Ignite  the  precipitate  strongly, 
let  the  crucible  partially  cool,  throw  p  a  small  lump  of  clean 
ammonium  carbonate,  and  heat  rapidly  again  to  bright  redness  in 
order  to  remove  traces  of  sulphuric  acid.  The  weighed  titanic 
acid,  notwithstanding  all  precautions,  is  likely  to  contain  a  little 
ferric  oxide.  Fuse  it  with  sodium  carbonate,  add  gradually  to  the 
cold  fused  mass  in  the  crucible  5  or  6  c.  c.  strong  sulphuric  acid, 
heat  till  evolution  of  CO2  has  ceased  and  the  mass  has  dissolved. 
Add  then  more  strong  sulphuric  acid  (6 — 10  c.  c.)  and  dilute  with 
about  100  c.  c.  of  water.  Determine  the  iron  in  this  solution  by 
titration  with  potassium  permanganate,  with  previous  reduction  by 
H2S  according  to  §  113,  3.  (Zinc  cannot  in  this  case  be  employed 
for  the  reduction  since  it  reduces  also  titanic  acid.)  Calculate  the 
iron  found  as  ferric  oxide  and  subtract  it  from  the  impure  titanic- 
acid  weighed. 

If  the  t  analyst  has  at  hand  hydrofluoric  acid  and  a  platinum 
dish  capable  of  holding  100  to  200  c.  c.,  the  following  method  of 
decomposing  the  ore  may  be  substituted,  with  great  saving  of  time, 
for  the  fusion  with  disulphate.  Heat  the  ore  nearly  to  boiling  in 
the  platinum  dish  with  a  mixture  of  hydrofluoric  and  strong  hydro- 
chloric acids.  Magnetic  iron  ores,  in  which  it  is  oftenest  required 
to  determine  titanic  acid,  are  thus  usually  decomposed  in  a  few 
minutes.  Add  20  to  25  c.  c.  concentrated  sulphuric  acid  diluted 
with  half  its  volume  of  water,  and  concentrate  by  means  of  a  care- 
fully adjusted  flame  till  fumes  of  sulphuric  acid  begin  to  escape. 
It  is  of  utmost  importance  to  remove  every  trace  of  hydrofluoric 
acid.  The  appearance  of  fumes  of  sulphuric  acid  can  be  considered 
as  proof  that  this  has  been  effected  only  when  means  are  employed 
to  protect  the  sides  of  the  dish  above  the  liquid  from  heat  sufficient  to 
volatilize  sulphuric  acid,  since  the  mixed  acids  are  attracted  upward 
along  the  surface  of  the  platinum.  After  cooling  add  nearly  100 
c.  c.  of  water.  Either  at  once  or  in  a  few  hours  the  whole  dis- 
solves, with  exception  perhaps  of  a  slight  residue,  which  may,  if  it 


§  217.]  COMPLETE  ANALYSIS   OF   IRON   ORES.  753 

appears  too  considerable  to  be  neglected,  be  subjected  again  to  the 
same  treatment.*  The  solution  of  the  ore  obtained  in  this  way  is 
neutralized  with  sodium  carbonate  and  further  treated  in  the  same 
manner  as  a  solution  obtained  by  decomposing  with  potassium 
disulphate.] 


[IT.  COMPLETE  ANALYSIS  OF  IKON  OKES. 
§  217. 

(Process  adapted  to  all  iron  ores  except  such  as  contain  a  large 
amount  of  titanic  acid.) 

1.  Silica,  iron,  aluminium,  manganese,  calcium,  magnesium. 

Take  about  1  grm.  ore.  Add  concentrated  hydrochloric  acid  and 
heat  in  a  water  bath  or  sand  bath  nearly  to  boiling  one  or  two 
hours.  Evaporate  finally  to  dryness  and  expose  the  residue  to  a  heat 
slightly  exceeding  100°  C.  in  order  to  render  insoluble  any  silica 
which  may  have  been  dissolved.  A  porcelain  dish  may  be  used 
in  this  operation,  but  a  beaker  of  200  to  300  c.c.  capacity  is  more 
convenient,  especially  if  a  suitable  air  bath  is  at  hand  for  raising 
the  temperature  at  the  end  to  120  to  130°  C.  Add  two  or  three 
c.c.  concentrated  hydrochloric  acid  to  the  residue  and  warm  till 
the  iron  is  redissolved,  and  filter  at  oncef  after  suitable  dilution, 
carefully  removing  every  particle  of  the  residue  to  the  filter; 
wash  and  reserve  the  filtrate ;  ignite  the  filter  and  its  contents  till 
carbon  is  burned  away ;  add  then  to  the  residue  5  or  6  times  its 
weight  of  pure  sodium  carbonate  and  fuse ;  disintegrate  the 
fused  mass  by  heating  with  water,  acidify  with  hydrochloric  acid, 
and  separate  silica  by  evaporation  and  drying  in  the  usual  manner. 
The  filtrate  from  the  silica  is  now  added  to  the  other  reserved 
solution  of  basic  metals. 

Another  method  of  decomposing  the  ore  and  separating  silica 
is  to  fuse  directly  with  sodium  carbonate,  without  previous  treat- 

*  If  the  ore  contains  much  calcium,  a  residue  of  calcium  sulphate  insoluble  in 
the  limited  amount  of  water  above  recommended  must  be  expected. 

f  By  prolonged  digestion  of  this  residue  with  hydrochloric  acid,  traces  of 
silica  might  be  taken  up  from  certain  silicates  which  being  very  slowly  acted  on 
by  acid  may  have  escaped  complete  decomposition  by -the  first  treatment  with 
acid. 


754  SPECIAL   PART.  [§217. 

ment  with  hydrochloric  acid,  and  separate  silica  from  the  fused 
mass  in  the  ordinary  manner.  More  time,  however,  is  required  to 
disintegrate  the  mass  and  separate  the  silica,  more  saline  matter  is 
introduced  into  the  solution,  and  the  platinum  crucible  used  for  the 
fusion  is  likely  to  become  permeated  with  iron  to  such  an  extent 
that  for  a  long  time  it  is  unsuitable  for  most  other  uses.  These 
disadvantages  overbalance  the  apparent  greater  simplicity  of  this 
mode  of  proceeding. 

From  the  solution  of  basic  metals  precipitate  first,  the  iron  as 
basic  ferric  acetate  according  to  direction  given  in  §  160,  71,  p. 
517.  The  iron  may  be  precipitated  without  concentration  of  the 
two  mixed  filtrates  if  care  has  been  taken  to  avoid  too  large  a  vol- 
ume and  the  presence  of  an  unnecessary  amount  of  free  acidr 
otherwise  the  solution  should  be  concentrated  until  the  greater 
part  of  the  free  acid  is  removed.  It  is  usually  best  to  collect  the 
precipitated  ferric  acetate  on  two  filters.  Wash  at  first  with 
boiling  hot  water  containing  1  or  2  per  cent,  of  sodium  acetate 
until  a  few  drops  of  the  washings  give  but  a  slight  turbidity  when 
tested  with  silver  nitrate.  Reserve  the  filtrate  and  washings 
which  contain  manganese,  calcium  and  magnesium,  and  continue 
without  interruption  to  wash  the  precipitate  with  hot  water  to 
which  a  little  ammonium  acetate  has  been  added  until  a  drop  of 
the  washings  leaves  no  residue  on  evaporation  on  platinum  foil. 
The  last  washings  containing  ammonium  acetate  are  thrown  away. 
Dry  the  precipitate,  which  contains  besides  iron  the  aluminium  and 
phosphoric  acid  of  the  ore,  detach  from  the  filters,  incinerate  the 
latter  with  prolonged  exposure  to  the  air  at  a  full  red  heat  in  order 
to  convert  into  ferric  oxide  the  lower  oxides  of  iron  formed  by 
reducing  action  of  the  filter  paper.  Add  the  precipitate  and 
moisten  it  in  the  crucible  with  concentrated  nitric  acid,  dry  with 
gentle  heat,  repeat  the  moistening  with  nitric  acid  and  drying, 
ignite  and  weigh.  The  weighed  precipitate  should  exhibit  no 
magnetic  attraction  when  a  magnet  is  applied  externally  to  the 
bottom  of  the  crucible.* 

Dissolve  the  weighed  FeaO3,Al2O3  and  P2  O6in  strong  hydro- 

*  If  the  treatment  with  nitric  acid  is  omitted,  lower  oxides  of  iron  are  usually 
formed  by  ignition  of  basic  ferric  acetate  which  are  converted  into  ferric  oxide 
with  great  difficulty  by  prolonged  ignition.  Even  treatment  with  nitric  acid 
lias  but  little  oxidizing  effect  after  the  precipitate  has  once  been  ignited. 


§  217.]  COMPLETE  ANALYSIS   OF  IRON   ORES.  755 

chloric  acid,  add  10  to  15  c.c.  of  pure  dilute  sulphuric  acid,  remove 
all  the  hydrochloric  acid  by  evaporation,  and  dilute  moderately 
with  water.  Occasionally,  but  not  often,  a  residue  of  silica  may  be 
observed  at  this  point,  so  considerable  in  quantity  as  to  render  it 
advisable  to  collect  it  in  a  small  filter  and  deduct  its  weight  from 
the  precipitate  which  contained  it  and  add  it  to  that  of  the  main 
portion  of  silica,  It  is  necessary  now,  in  order  to  estimate  satisfac- 
torily the  comparatively  small  amount  of  aluminium  usually 
present,  to  determine  very  accurately  the  iron.  Titration  with 
potassium  permanganate  in  the  sulphuric  acid  solution  is  the  best 
of  all  volumetric  methods;  previous  reduction  with  hydrogen 
sulphide  according  to  directions  on  p.  729  is  to  be  recommended 
as  a  method  of  reduction  involving  least  sources  of  error.  The  A12 
O3  is  calculated  by  deducting  Fe2O3  found,  and  also  P3O5* 
(determined  in  another  portion  of  the  ore)  from  the  joint  weight 
of  the  three  substances. 

Concentrate  the  filtrate  from  the  basic  ferric  acetate  to  about 
600  c.c.  and  precipitate  manganese  with  bromine  water  after 
partial  neutralization  of  the  free  acetic  acid  as  directed  on  p. 
749  (second  method  of  determining  manganese).  Neutralize  the 
filtrate  from  the  manganese  dioxide  with  ammonia  and  precipitate 
calcium  with  ammonium  oxalate.  In  the  filtrate  from  calcium 
oxalate  precipitate  (without  concentration  unless  the  volume 
exceeds  600  c.c.)  the  magnesium  with  sodium  phosphate  adding  a 
liberal  quantity  of  ammonia  and  allowing  24  hours  for  complete 
separation  of  the  ammonium  magnesium  phosphate. 

2.  Alkalies. 

Small  quantities  of  potash  or  soda  are  sometimes  found  in 
magnetic  iron  ores  owing  to  the  presence  of  felspars.  More 
rarely  an  appreciable  amount  of  potash  may  be  found  in  brown 

*If  the  amount  of  P2O5  is  very  small,  not  exceeding  say  O'l  per  cent,  the 
precipitate  produced  by  boiling  with  sodium  acetate,  instead  of  being  treated  as 
here  recommended,  may  be  washed  sufficiently  to  free  it  from  appreciable 
quantities  of  manganese  and  alkali-earth  metals,  dissolved  in  hydrochloric  acid 
and  reprecipitated  with  ammonia.  The  ferric  and  aluminium  hydroxides  thus 
precipitated  are  easily  washed  free  from  saline  matter,  ignited  and  weighed. 
The  phosphoric  acid,  however,  is  liable  to  be  but  partially  precipitated  by 
ammonia  along  with  the  iron,  so  that  an  error  (not  exceeding  the  amount  of  PS 
O5)  will  result  in  calculating  the  A12O3  by  difference. 


756  SPECIAL    PART.  [§  217. 

hematite  on  account  of  intermixed  micaceous  minerals.  For 
qualitative  or  quantitative  examination  use  the  method  of  J.  L. 
SMITH.  See  p.  426. 

3.  Ferrous  and  Ferric  Oxides. 

Decompose  *5  grin,  by  boiling  in  a  large  covered  platinum  cruci- 
ble with  a  mixture  of  sulphuric  and  hydrofluoric  acids,  dilute  and 
determine  ferrous  iron  by  titration  with  potassium  permanganate. 
(See  p.  529).  The  amount  of  ferric  oxide  can  of  course  then  be 
calculated,  fhe  total  iron  having  being  previously  determined. 

4.  Carbonic  Acid. 

Determine  carbonic  acid  in  1  to  5  grm.  according  to  the  amount 
present  by  decomposing  with  hydrochloric  acid  and  weighing  the 
evolved  CO3  by  the  process  described  on  p.  413.  Or  determine 
carbonic  acid  and  water  at  the  same  time  by  igniting  in  a  com- 
bustion tube  with  lead  chromate  and  potassium  chromate.  (See 
Analysis  of  Silicates  and  Siliceous  Rocks,§  208,  p.  716).  The 
latter  method,  however,  cannot  be  used  when  the  ore  contains 
carbonaceous  matter. 

5.  Water. 

When  carbonic  acid  and  ferrous  oxide  are  absent,  water  is 
determined  by  loss  on  ignition.  Water  should  be  determined  in 
the  same  pulverized  sample,  kept  carefully  corked  in  a  tube, 
which  has  been  used  for  the  determination  of  the  chief  constit- 
uents. If  the  sample  has  not  been  previously  dried  at  100°  C., 
hygroscopic  and  combined  water  may  be  determined  separately  (if 
desired)  by  drying  a  weighed  portion  (about  1  grm.)  at  100°  C.  to 
constant  weight  in  a  platinum  crucible  and  afterwards  igniting. 

In  the  presence  of  carbonic  acid  or  ferrous  oxide  determine 
water  by  igniting  1  or  2  grm.  in  a  platinum  boat  in  a  combustion 
tube  and  collecting  the  water  in  a  calcium  chloride  tube,  a  slow 
current  of  dried  air  being  meanwhile  drawn  through  the  apparatus 
by  an  aspirator.  Or  the  water  and  at  the  same  time  carbonic 
acid  may  be  determined  as  suggested  above  (under  4.  Carbonic  Acid). 

6.  Presence  of  carbonaceous  or  bituminous  matter  interferes 
with  determination  of  water  by  either  of  the  above  methods,  and 
also  requires  a  modification  of  the  processes  used  for  determining 
some  of  the  other  constituents.     Sulphur  should  be  determined  in 


§  217.]  COMPLETE    ANALYSIS    OF   IKOX    ORES.  757 

the  ore  without  previous  ignition,  as  directed  in  §  216  ;  carbonic 
acid  by  decomposition  with  hydrochloric  acid,  and  weighing  the 
evolved  CO2,  as  described  p.  413.  In  determining  phosphorous 
according  to  §  216,  ignite  the  portion  weighed  out  in  an  open 
crucible  till  carbon  is  burned  out  before  dissolving  it.  Treat  also 
in  the  same  manner  the  weighed  portion  in  which  silica  and  the 
other  chief  constituents  are  to  be  determined. 

For  the  estimation  of  ferrous  &nd  ferric  oxides  decompose  *5  gr. 
with  a  mixture  of  hydrochloric  and  hydrofluoric  acids,  proceeding 
as  in  3.  Since  presence  of  organic  matter  may  interfere  with  the 
volumetric  determination  of  either  ferrous  or  ferric  iron,  separate 
ferric  iron  by  barium  carbonate  with  exclusion  of  air,  according  to 
§  160,  p.  513.  Determine  the  amount  of  ferric  iron  thus  precipi- 
tated by  dissolving  in  sulphuric  acid,  reduction  to  ferrous  sulphate, 
and  titration  with  potassium  permanganate. 

From  the  results  of  these  several  operations  the  composition  of 
the  ore  in  its  original  state  can  now  be  calculated,  with  the  excep- 
tion of  water  and  carbonaceous  matter. 

7.  Titanic  acid. 

It  is  rarely  or  never  necessary  to  make  complete  analyses  of  iron 
ores  containing  over  5  or  6  per  cent,  of  titanic  acid,  since  such  ores 
are  usually  rejected  as  unsuitable  for  smelting.  When  ores  con- 
taining this  amount  or  less  are  subjected  to  the  above-described 
process  of  analysis,  a  portion  of  the  titanic  acid  follows  the  silica 
and  is  weighed  along  with  it.  The  remainder  is  precipitated  with 
the  basic  ferric  acetate  and  is  weighed  with  ferric  oxide.  A 
method  of  separating  the  titanic  acid  from  these  two  products  is 
described  in  §  208  (Analysis  of  Silicates  and  Siliceous  Rocks),  p.  717. 
In  washing  silica  which  contains  titanic  acid,  the  latter  sometimes 
passes  through  the  pores  of  the  paper,  making  the  filtrate  turbid. 
This,  however,  will  occasion  no  error  if  the  filter  retains  the  silica. 

8.  Phosphoric  acid  must  be  determined  in  a  separate  portion 
of  the  ore  as  in  §  216. 

9.  Sulphur  must  also  be  determined  in  a  separate  portion  as  in 
216. 


758  SPECIAL   PART.  [§  218. 


[18.  ANALYSIS  OF  PIG-IKON,  STEEL,  AND  WROUGHT 

IRON. 

§  218. 

I.  PIG-IRON. 

Preparation  of  the  sample. 

The  chemist  usually  receives  for  analysis  a  short  section  broken 
from  a  pig.  If  the  iron  is  hard  and  brittle  (white  pig  or  spiegel), 
procure,  by  breaking  on  an  anvil  with  a  heavy  hammer,  some  frag- 
ments free  from  the  outer  surface,  to  which  sand  or  other  impuri- 
ties may  adhere.  Pulverize  these  fragments  to  a  coarse  powder  in 
a  mortar  of  the  hardest  steel.  If  the  sample  is  too  tough  to  be 
crushed,  it  must  be  reduced  to  a  suitable  condition  by  drilling.* 
To  obtain  the  necessary  quantity  (40  to  50  grm.)  bore  one  or  more 
holes  in  the  clean  broken  end  of  the  sample,  at  a  distance  half  way 
between  the  centre  and  outside.  Use  no  oil  or  water  in  the  process, 
and  cleanse  the  drill  from  oil  before  beginning.  The  borings  may 
be  taken  up  from  time  to  time  during  the  operation  with  a  magnet 
and  transferred  to  a  bottle  provided  with  a  glass  stopper. 

1.  Determination  of  the  total  amount  of  carbon. 

Method  of  BEKZELIUS  (somewhat  modified). 
The  determination  of  carbon  by  the  method  here  recommended 
requires  the  use  of  a  special  reagent,  viz.,  a  strong  solution  of 
cupric  ammonium  chloride  containing  no  free  acid.  This  solution 
may  be  prepared  as  follows :  Dissolve  common  blue  vitriol  (crys- 
tallized cupric  sulphate)  in  10  to  15  times  its  weight  of  water,  filter 
the  solution,  and  heat  to  boiling  in  a  copper  kettle.  Add  solution 
of  common  sal  soda  gradually  to  alkaline  reaction,  keeping  up 
meanwhile  the  boiling.  Basic  cupric  carbonate  (not  entirely  free 
from  basic  sulphate)  is  precipitated  in  a  dense  form  easy  to  wash 
by  decantation.  Wash  it  by  decantation  until  the  sodium  sul- 
phate is  nearly  all  removed.  Transfer  to  a  glass  or  porcelain 
vessel.  Reserve  about  one  tenth,  and  dissolve  the  remainder  in 
concentrated  hydrochloric  acid  ;  add  the  reserved  portion  which  is 


*  It  is  best  if  possible  to  employ  the  assistance  of  a  machinist  who  can  use  a 
drill  press  run  by  steam. 


§  21."-  FKr-iRox,  STP:KL.  AXD  WROUGHT  IRON.  759 

designed  to  neutralize  the  acid  completely.  Let  the  solution  stand 
<3old  several  hours  with  occasional  agitation.  A  portion  of  the 
basic  carbonate  should  remain  permanently  undissolved.  Filter, 
and  add,  for  five  parts  blue  vitriol  used,  two  parts  ammonium 
chloride  previously  dissolved  in  a  small  volume  of  hot  water  and 
filtered.  Care  should  be  taken  to  conduct  the  above  operations 
so  that  the  final  solution  obtained  may  not  be  too  dilute.  If  its 
volume  does  not  exceed  twice  the  volume  of  the  concentrated 
hydrochloric  acid  used  in  dissolving  the  carbonate,  it  is  satisfactory 
in  respect  to  strength. 

The  Process.  Pour  at  once,  not  gradually,  at  least  200  c.c.  of 
the  cupric  ammonium,  chloride  solution  upon  the  iron  borings  (3  or 
-i  grm.  may  be  taken)  in  a  large  beaker.  The  beaker  should  be  set 
in  a  vessel  of  cold  water,  and  the  contents  should  be  frequently 
stirred  during  the  first  15  or  20  minutes  to  prevent  too  great  ele- 
vation of  temperature  by  the  chemical  action ;  otherwise  a  slight 
evolution  of  hydrogen  might  take  place,  carrying  off  with  it  some 
hydrocarbon  compound.  (Evolution  of  hydrogen  and  loss  of  car- 
bon is  sure  to  result  if  the  cupric  ammonium  chloride  contains  free 
acid.)  Afterwards  the  beaker  is  allowed  to  remain  at  the  common 
temperature  of  the  room.  The  iron  dissolves  as  ferrous  chloride 
with  deposition  of  metallic  copper,  which,  in  presence  of  excess  of 
cupric  chloride,  is  converted  into  cuprous  chloride.  The  latter  is 
soluble  in  the  cupric  ammonium  chloride.  After  the  metallic  iron 
has  all  dissolved,  leaving  a  residue  which  crumbles  under  pressure 
(6  to  12  hours  may  be  required  according  to  fineness  of  the  borings), 
add  a  few  c.c.  of  hydrochloric  acid  to  dissolve  ferric  compounds 
which  may  be  deposited  by  the  action  of  the  air  on  the  ferrous 
chloride  in  solution.  If,  after  standing  several  hours  longer,  an  accu- 
mulation of  metallic  copper  or  cuprous  chloride  is  observed  remain- 
ing persistently  undissolved,  more  of  the  double  chloride  may  be 
added.  The  complete  solution  of  iron  and  copper  is  generally 
effected  in  48  hours,  and  often  much  sooner.  When  nothing 
remains  undissolved  except  a  black  carbonaceous  residue,  filter 
through  an  asbestos  filter  prepared  by  packing  well-disintegrated 
asbestos,  neither  too  closely  nor  too  loosely,*  in  a  tube  8  or  9  inches 


*  Let  the  first  2  cm.  of  the  filtering  tube  at  the  very  bottom  have  a  diameter 
of  4  cm.  and  the  next  2  cm.,  above  a  diameter  of  about  1  cm.  Leave  the  lower 
2  cm.  empty  and  fill  with  asbestos  to  a  point  a  little  above  where  the  tube  has 
its  full  diameter.  After  filling,  pour  water  into  the  tube;  if  it  runs  through  in 
a  continuous  stream,  the  packing  is  too  loose,  but  it  should  drop  rapidly. 


700  SPECIAL    PAKT. 

long  and  f  of  an  inch  in  diameter,  narrowed  at  one  end.  Wash  the 
carbon  residue  until  the  copper  solution  is  completely  removed.  It 
is  not  safe  to  apply  an  exhausting  apparatus  to  hasten  the  filtration 
with  a  filter  prepared  in  this  manner.*  Dilute  the  filtrate  with  dis- 
tilled (or  perfectly  clear)  water,  and  observe  whether  particles  of  the- 
carbon  residue  have  passed  through.  Dry  the  residue  in  the  tube  at 
100°,  and  determine  the  amount  of  carbon  in  it  by  combustion 
with  lead  chromate  mixed  with  potassium  dichromate  according 
to  §  ITT.  Remove,  for  this  purpose,  the  carbon  residue  together 
with  the  asbestos  from  the  tube  with  the  aid  of  a  steel  wire  slightly 
curved  at  the  end,  introducing  it  through  the  narrow  end  of  the 
tube,  loosening  and  pushing  the  w^hole  mass  out  into  a  small  porce- 
lain mortar  already  containing  some  of  the  chromates.  Rinse  out 
the  tube  with  the  remainder  of  that  portion  of  the  chromates 
which  is  to  be  mixed  with  the  substance,  and  mix  with  a  pestle  in 
the  mortar  till  the  asbestos  is  broken  up  to  such  an  extent  that  the 
mixture  can  be  introduced  into  the  combustion  tube  through  a 
funnel. 

2.  Determination  of  the  graphite. 

Treat  4  grm.  with  moderately  concentrated  hydrochloric  acid,  at 
a  gentle  heat,  until  no  more  gas  is  evolved;  filter  the  solution 
through  an  asbestos  filter  prepared  as  in  1 ;  wash  the  undissolved- 
residue,  first  with  boiling  water,  then  with  solution  of  potassa,  after 
this  with  alcohol,  and  lastly  with  ether ;  then  dry,  and  burn  after 
§  ITT.  Deduct  the  graphite  obtained  here  from  the  total  amount 
of  carbon  found  in  1  ;  the  difference  gives  the  combined  carbon. 

3.  Determination  of  Sulphur. 

The  general  plan  adopted  in  all  good  methods  of  determining 
sulphur  in  iron  is  to  dissolve  the  metal  as  completely  as  is  prac- 
ticable in  hydrochloric  acid,  whereby  the  greater  part  of  the  sul- 
phur, being  converted  into  hydrogen  sulphide,  passes  off  along 
with  a  large  volume  of  hydrogen  which  is  conducted  through  some- 
liquid  capable  of  absorbing  the  II8S.  For  this  purpose  bromine 
dissolved  in  hydrochloric  acid,  potassium  permanganate  solution,. 


*  J.  CREAGH  SMITH  has  devised,  and  described  in  the  America!  Chemical 
Journal,  vol.  i..  p.  368,  an  asbestos  filter  for  filtering  carbon  residues,  which  is 
simple  in  construction,  and  can  be  used  with  the  BUNSEN  pump. 


§  218.]  PIG-IKON,  STEEL,  AND  WROUGHT   IRON.  761 

alkaline  lead  solution,  ammoniacal  cadmium  solution,  ammoniacal 
silver  solution  have  all  been  employed,  some  suitable  method  in 
each  case  being  devised  for  bringing  the  absorbed  sulphur  into  a 
weighable  form.  Only  the  method  in  which  an  ammoniacal  silver 
is  used  will  here  be  described  in  detail. 

.  A  flask  of  300  to  350  c.c.  capacity  is  provided 
with  a  doubly  perforated  rubber  stopper.  Through  one  hole 
passes  a  funnel  tube  for  the  introduction  of  acid.  The  end  of  this 
tube,  which  should  reach  nearly  to  the  bottom  of  the  flask,  is  drawn 
out  narrower  and  bent  upward  with  a  short  curve  to  prevent  gas 
bubbles  from  entering  it  and  escaping.  For  absorbing  the  hydro- 
gen sulphide  from  the  evolved  gas  a  pair  of  connected  U-tubes  are 
used  like  those  in  fig.  64,  p.  435.  The  absorbing  tubes  are  con- 
nected with  the  flask  by  a  strong  (not  too  narrow)  tube  about  & 
inches  long,  bent  downward,  and  contracted  if  necessary,  at  each 
end,  so  as  to  fit  into  the  perforation  in  the  stopper. 

Treat  the  rubber  stoppers  used  in  making  connection  with  warm 
soda  solution,  and  carefully  rub  the  loosened  sulphur  from  the 
surface,  not  neglecting  the  perforations,  till  a  clean  black  surface 
is  obtained. 

The  process.  Dissolve  a  gramme  or  more  of  silver  nitrate  in 
15  to  20  c.c.  of  ammonia  solution.  Pour  at  least  10  c.c.  of  this 
solution  into  the  first  U-tube  and  the  remainder  into  the  second. 
A  little  water  may  be  added  if  the  size  and  form  of  the  U-tubes 
require  it,  in  order  to  secure  proper  contact  with  the  gas  bubbles 
which  are  to  pass  through  them.  Introduce  10  grm.  of  the  iron  and 
40 — 50  c.c.  water  into  the  flask.  Adjust  the  funnel  tube  so  that 
the  lower  end  may  be  under  the  surface  of  the  water.  Connect 
the  several  parts  of  the  apparatus,  and  add  concentrated  hydro- 
chloric acid  in  small  portions  at  a  time  so  as  to  produce  as  nearly 
as  practicable  a  constant  evolution  of  gas.  The  addition  of  acid 
may  be  regulated  according  to  the  appearance  of  the  §econd  IT-tnbe. 
The  first  tube  should  absorb  the  hydrogen  sulphide.  If  a  blacken- 
ing of  the  solution  in  the  second  tube  begins  to  appear,  add  the 
hydrochloric  acid  more  gradually.  When  (usually  after  4  or  5 
hours)  the  addition  of  more  hydrochloric  acid  fails  to  increase  the 
very  slow  evolution  of  gas,  heat  the  flask  gently,  but  not  to  boiling, 
20  or  30  minutes,  with  addition  of  more  hydrochloric  acid,  taking 
care  not  to  distil  over  enough  acid  to  neutralize  the  ammonia  in 
the  first  F-tube.  Collect  the  precipitate  formed  in  the  first  tube 


762  SPECIAL   PART.  [§  218. 

on  a  small  filter,  wash  slightly,  and  dry  at  100°  C.  Dry  also  the 
U-tnbe,  to  which  a  portion  of  the  precipitate  invariably  adheres. 
The  second  tube  will  not  contain  an  appreciable  quantity  of  silver 
sulphide  unless  too  rapid  a  current  of  gas  has  been  unintentionally 
produced.  Place  the  dry  filter  and  its  contents  in  a  small  dry 
beaker.  Dissolve  or  loosen  the  sulphide  of  silver  from  the  U-tube 
by  shaking  with  successive  portions  of  aqua  regia  and  pouring  into 
a  small  beaker,  using  in  all  about  20  c.c.  Then  put  into  the  beaker 
the  dried  silver  sulphide  with  the  filter. 

The  insoluble  residue  in  the  flask,  consisting  chiefly  of  graphite 
and  silica,  often  contains  sulphur,  and  should  never  be  neglected 
in  the  analysis  of  pig-irons.  Collect  it  on  a  filter  and  wash  out  the 
free  acid,  dry  on  the  filter  thoroughly  at  100°,  detach  from  the 
filter  carefully,  rub  the  mass  to  a  powder  in  a  beaker  with  a  glass 
rod,  and  add  aqua  regia. 

Allow  the  aqua  regia  to  act  on  the  two  products  at  the  common 
temperature  6  hours,  and  afterwards  12  to  24  hours,  at  40°  to  54°  C. 
Then  concentrate  to  one  third  the  first  volume,  dilute,  and  filter  each 
through  separate  filters  and  unite  the  filtrates.  After  concentrating 
to  about  50  c.c.  add  barium  chloride,  and  continue  the  concentration 
not  quite  to  dryness,  but  till  only  liquid  enough  remains  to  moisten 
the  residue.  Add  a  small  volume  of  water  and  5  or  6  drops  of 
hydrochloric  acid.  Treat  the  residue  of  impure  barium  sulphate 
thus  obtained  as  in  the  determination  of  sulphur  in  iron  ores  (p. 
746). 

The  aqua  regia  used  for  oxidizing  the  silver  sulphide  and  the 
insoluble  residue  must  be  tested  for  sulphuric  acid  as  directed  in 
"  Analysis  of  Iron  Ores,"  p.  746.  The  process  of  dissolving  the 
iron  in  the  flask  should  be  carried  on  without  interruption. 

This  method  gives  results  agreeing  with  remarkable  closeness 
when  repeated  determinations  are  made  in  the  same  sample. 

The  substitution  of  a  hydrochloric  acid  solution  of  bromine  for 
the  solution  of  silver  nitrate  in  ammonia  requires  no  essential 
change  in  the  details  of  the  process.  The  apparatus,  however, 
must  be  modified  so  as  to  avoid  much  contact  of  rubber  stoppers 
with  the  bromine  vapor.  The  bromine  solution  at  the  close  of  the 
operation  contains  the  sulphur  which  has  been  evolved  at  HaS 
already  in  the  form  of  sulphuric  acid,  which  can  be  determined 
simply  by  precipitation  with  barium  chloride  after  evaporating  off 
the  hydrochloric  acid  to  the  proper  extent.  But  since  the  insoluble 


§  218.]  PIG-IRON,    STEEL,  AND    WROUGHT   IROX.  763 

residue,  when  accurate  results  are  desired,*  must  be  treated  for 
sulphur,  as  before  described,  there  is  little  saving  of  time  or 
trouble  by  this  shorter  method  of  determining  the  sulphur  which 
passes  into  the  U-tube. 

4.  Determination  of  Phosphorus. 

If  the  iron  is  known  to  contain  over  0*5  per  cent,  of  phosphorus 
2  grm.  will  suffice.  If  less  is  present  4  grm.  may  be  taken  for  the 
determination. 

Dissolve  with  a  mixture  of  equal  parts  of  concentrated  nitric 
and  hydrochloric  acids,  using  about  30  c.c.  per  gramme  of  iron 
taken,  and  pouring  the  whole  quantity  upon  the  iron  at  once.f 

Proceed  further  in  all  details  precisely  as  directed  for  deter- 
mination of  phosphorus  in  iron  ores. 

5.  Determination  of  Silicon. 

The  residue  from  the  solution  used  for  determining  phosphorus 
may  be  used  for  determining  silicon.  Ignite  it  without  separation 
from  the  filter  until  the  graphite  is  partially  burned  away.  Fuse 
with  sodium  carbonate  mixed  with  a  little  potassium  nitrate,  suffi- 
cient to  effect  complete  combustion  of  the  carbon  still  present. 
Treat  the  fused  mass  first  with  boiling  water,  in  which  it  readily 
dissolves,  except  some  silica  in  light  flocculent  form,  and  traces  of 
metallic  oxides.  Acidify  with  hydrochloric  acid,  or  nitric  acid  in 
case  the  solution  is  to  be  in  contact  with  platinum,  and  separate 
silica  as  usual.  When  the  quantity  of  silica  is  not  over  1  per  cent., 
these  operations  may  be  most  conveniently  performed  in  a  large 
platinum  crucible  without  transferring  the  substance  to  any  other 
vessel. 

6.  Determination  of  Manganese. 

Dissolve  3  grm.  in  aqua  regia,  evaporate  to  dryness  to  separate 

*  I  have  frequently  determined  separately  the  sulphur  remaining  in  the 
insoluble  residue  obtained  by  treating  pig-iron  as  described  in  this  process,  and 
seldom  find  it  to  be  free  from  a  weighable  quantity  of  sulphur;  in  spme  cases 
amounting  even  to  one  third  of  the  total  amount  found. — O.  D.  A. 

f  If  the  mixture  of  acids  is  gradually  added  to  the  iron,  especially  if  a  larger 
proportion  of  hydrochloric  is  used,  a  possible  escape  of  phosphoretted  hydrogen 
may  be  apprehended. 


764  SPECIAL   PART.  [§  218, 

silica,  redissolve  with  hydrochloric  acid,  filter,  and  determine  man- 
ganese in  the  solution  as  in  iron  ores.     Method  1,  p.  747. 

In  spiegel-iron  the  manganese  may  be  more  accurately  deter- 
mined by  dissolving  *5  grm.,  evaporating  to  dryness,  redissolving 
with  hydrochloric  acid,  and  proceeding  with  the  solution  as  in 
Method  2  for  iron  ores  (p.  749). 

7.  Determination  of  Copper. 

If  a  determination  of  the  minute  quantity  of  capper  sometimes 
present  in  pig-iron  is  required,  it  may  be  done  in  the  same  portion 
used  for  sulphur.  Dilute  the  filtrate  from  the  first  insoluble 
residue  and  pass  hydrogen  sulphide  through  it  nearly  an  hour. 
More  or  less  sulphur  separates.  Allow  it  several  hours  to  settle. 
If  the  deposit  is  darker  in  color  than  pure  sulphur,  presence  of 
copper  is  indicated.  In  that  case  collect  it  on  a  filter  and  wash 
with  a  dilute  solution  of  hydrogen  sulphide.  Copper  is  also  often 
found  in  the  insoluble  residue.  When  this  residue  is  treated  with 
aqua  regia  to  extract  the  sulphur  possibly  retained  by  it,  the  copper 
is  dissolved  and  goes  finally  into  the  filtrate  from  the  impure 
barium  sulphate  first  obtained.  Pass  H2S  through  this  filtrate  and 
filter  off  any  precipitate  which  may  result. 

Incinerate  the  two  filters  containing  the  copper  precipitates  in 
a  porcelain  crucible.  Treat  the  residue  in  the  crucible  with  aqua 
regia,  add  finally  a  few  drops  of  sulphuric  acid,  remove  the  other 
acids  by  evaporation,  take  up  the  cupric  sulphate  in  a  small  volume 
of  water,  filter  and  precipitate  the  copper  again  with  H3S,  and 
weigh  it  as  cuprous  sulphide. 

8.  Presence  of  Other  Mements  in  Pig-Iron. 

Besides  the  above-mentioned  elements,  sodium,  potassium, 
lithium,  calcium,  magnesium,  aluminium,  chromium,  titanium, 
zinc,  cobalt,  nickel,  tin,  arsenic,  antimony,  vanadium,  and,  accord- 
ing to  some  authorities,  nitrogen,  may  occur  in  minute  quantities 
in  pig-iron.  Their  determination,  however,  is  rarely  undertaken  ; 
partly  because  it  is  not  known  whether  they  have  any  influence, 
good  or  bad,  on  the  quality  of  the  iron  when  present  in  such 
minute  proportions,  and  partly  because  it  is  very  difficult  to 
determine  them  accurately  on  account  of  lack  of  sufficiently 
pure  reagents,  the  action  of  solutions  on  the  vessels  used  in  the 
process,  &c. 


§  219.]  ANALYSIS    OF  ^COAL    AND    PEAT.  765 


II.  STEEL  AND  WROUGHT  IKON. 

Determine  carbon,  silicon,  sulphur,  phosphorus,  and  manganese 
as  in  pig-iron,  with  the  following  modifications  only  of  the  pro- 
cesses used  for  carbon,  silicon,  and  sulphur. 

Silicon  is  best  determined  in  a  separate  portion,  since  the  quan- 
tity used  for  phosphorus  does  not  afford  enough  silica  to  weigh 
accurately  ;  10  grm.  will  suffice.  Place  the  weighed  quantity  in  a 
platinum  (or  porcelain)  dish,  add  first  30  to  40  c.  c.  water ;  next, 
gradually,  concentrated  hydrochloric  acid  until  with  aid  of  heat 
the  metal  is  dissolved,  leaving  a  residue  of  more  or  less  carbona- 
ceous matter.  Evaporate  to  dry  ness,  expose  to  a  temperature  of 
120°  to  150°  C.  in  an  air-bath,  redissolve  the  iron  by  adding  first 
concentrated  hydrochloric  acid,  and  next  water.  Filter  through  a 
small  filter,  incinerate  the  filter  and  burn  the  carbon  out  of  the 
residue,  fuse  with  sodium  carbonate,  disintegrate  the  fused  mass 
with  water,  acidify  with  hydrochloric  acid,  and  separate  silica  by 
evaporating  in  the  crucible.  The  now  pure  silica  is  collected  in  a 
very  small  filter,  washed  and  weighed  in  the  usual  manner. 

In  the  analysis  of  Bessemer  steel,  or  any  steel  or  iron  which 
lias  been  melted,  it  may  be  assumed  that  the  silica  thus  obtained  is 
formed  by  oxidation,  in  the  process  of  analysis,  of  silicon  existing 
in  the  metal.  In  the  analysis  of  ordinary  wrought  iron  the  silica 
•obtained  may  come  partly  from  silicon  and  partly  from  mechani- 
cally mixed  particles  of  slag  in  which  it  existed  as  silica. 

Carbon.  Use  for  determination  6  to  10  grm.  of  steel  or  10  grm. 
of  wrought  iron. 

Sulphur.  Treat  the  comparatively  small  quantity  of  insoluble 
residue  collected  on  a  small  filter,  washed  and  dried,  directly  with 
aqua  regia  without  removing  from  the  filter.] 


19.  ANALYSIS  OF  COAL  AJSD  PEAT. 

§219. 

For  technical  purposes,  estimations  of  moisture,  ash,  coke,  and 
volatile  matters  usually  suffice.  Determination  of  sulphur  is  less 
frequently  required,  and  ultimate  analysis  is  only  resorted  to  in 
special  cases. 


766  SPECIAL   PABT.  [§  219. 

a.  Moisture.  The  finely  pulverized  coal  (3 — 5  grm.)  is  heated 
to  110° — 115°  for  an  hour  or  more  or  until  it  ceases  to  lose  weight 
(see  §  29).  Many  bituminous  coals  gain  weight  after  a  time  from 
oxidation  of  sulphides  or  hydrocarbons  (WHITNEY).  According 
to  HINKICHS,*  drying  the  coal  for  one  hour  effects  the  maximum 
loss. 

I.  Coke  and  volatile  matters.  The  dried  coal  of  a  is  sharply 
heated  in  a  closed  platinum,  or,  in  presence  of  sulphides,  in  a 
porcelain  crucible  as  long  as  combustible  matters  issue  from  it.  It 
is  then  cooled  quickly.  The  loss  is  set  down  as  volatile  matters. 
The  residue,  less  the  ash,  is. coke. 

G.  Ash.  The  residue  of  5  is  incinerated  in  a  crucible  placed 
aslant. 

d.  Carbon  and  hydrogen  are  determined  by  combustion  with 
chromate  of  lead  and  bichromate  of  potash,  §  177. 

e.  Sulphur  is  best  determined  according  to  §  186,  0,  2,  a,  p. 
658.     The  method  thus  described  gives  the  amount  of  ash  as  well 
as  sulphur. 

Or  the  following  simple  method  recommended  by  EscHKAf  may 
be  employed.  About  1  grm.  of  the  finely  -pulverized  substance  is 
intimately  mixed  by  stirring  with  a  platinum  wire  with  1  grm. 
burned  magnesia  (MgO)  and  '5  grm.  dry  sodium  carbonate  in  a 
platinum  crucible.  The  uncovered  crucible  is  then  heated  in  an 
inclined  position  with  an  alcohol  lamp  so  that  only  the  lower  half 
becomes  red  hot.  In  order  to  facilitate  combustion,  which  requires, 
according  to  the  nature  of  the  substance,  £  to  1  hour,  the  mixture  is 
frequently  stirred  with  a  platinum  wire.  After  the  carbon  is  con- 
sumed and  the  color  of  the  mass  has  changed  to  brownish  or 
yellowish,  \  to  1  grm.  of  pulverized  anhydrous  ammonium  nitrate 
is  added  and  intimately  mixed  with  the  contents  of  the  crucible. 
The  mixture  is  then  ignited  again,  in  the  covered  crucible,  from  5 
to  10  minutes.  Any  sulphites  which  may  have  been  formed  at 
first  are  hereby  converted  into  sulphates.  The  mixture,  which 
retains  its  pulverulent  form,  is  next  transferred  to  a  beaker  and 
warmed  with  150  c.  c.  of  water.  The  solution  is  filtered  and  acidi- 
fied with  hydrochloric  acid.  Sulphuric  acid  is  then  precipitated 
with  barium  chloride. 


Chemical  News,  19,  282.  f  Zeitschr.  f.  anal.  Chem.  13,  344. 


§  220.]          ANALYSIS   OF   COMMERCIAL   FERTILIZERS.  767 

All  the  sulphur,  whether  existing  in  the  form  of  calcium  sul- 
phate or  pyrites,  in  the  coal  is  obtained  by  this  method. 

The  sulphur  of  calcium  sulphate  in  coal  may  be  separately 
determined  by  boiling  24  hours  the  finely  powdered  coal  with  an 
equal  weight  of  sodium  carbonate  dissolved  in  water,  filtering, 
acidifying  with  hydrochloric  acid,  and  precipitating  with  barium 
chloride. 

The  calcium  sulphate  is  decomposed  by  the  sodium  carbonate, 
while  sulphides  of  iron  are  not  attacked. 


[20.  ANALYSIS  OF  COMMERCIAL  FERTILIZERS. 

§  220. 

1.  Preparation  of  the  sample.     Mix  the  sample  uniformly  and, 
if  need  be,  take  a  portion  of  20 — 50  grms.  which  shall  accurately 
represent  the  whole,  for  further  pulverization.     Bone,  dried  blood, 
guano,  &c.,  should  be  ground  or  pounded  fine  enough   to   pas* 
through  sieve  meshes  of  -^  in.  diameter. 

Superphosphates  should  be  merely  rubbed  in  a  mortar  to  crush 
lumps  and  secure  uniformity.  Grinding  of  superphosphates  may 
occasion  a  further  action  of  the  acid  on  the  undissolved  phosphate 
and  increase  the  per  cent,  of  soluble  phosphoric  acid. 

If  the  substance  is  very  moist  and  coarse  dry  20  to  50  grms.  at 
100°,  with  addition  of  a  weighed  amount  of  oxalic  acid  if  ammonia 
is  likely  to  escape,  till  it  can  be  easily  handled,  grind  fine  and  weigh. 
Make  nitrogen  determinations  in  this  portion  and  reckon  the  results 
back  to  the  original  material. 

ANALYSIS  OF  SUPERPHOSPHATE. 

2.  Soluble  Phosphoric  Acid.     Bring  20  giro,  into  a  litre  flask 
with  about  800  c.  c.  of  water  and  shake  frequently  (every  10  min- 
utes)  for   2   hours :    then   make  up  to  volume  of   1  litre ;  mix 
thoroughly,  pour  on  dry  filter  and  measure  off  100  c.  c.  =  2  grm. 
substance. 

3.  The  determination  of  phosphoric  acid  in  the  solution  thus 
obtained  may  be  made  most  accurately  by  the  molybdic  method. 
(See  p.  375). 

4.  A  simpler,  more  rapid  and  for  most   purposes  sufficiently 


768  SPECIAL   PART.  [§  220. 

accurate  process  is  the  following  "  citric  method,"  first  published 
in  its  present  form  by  PETERMANN,  but  worked  out  independently 
in  the  Connecticut  Agricultural  Experiment  Station,  as  follows : 

To  the  solution  add  55  c.  c.  solution  of  ammonium  citrate,* 
(equivalent  to  10  grin,  of  crystallized  citric  acid),  40  c.  c.  of  mag- 
nesia mixturef — in  all  cases  use  about  four  times  as  much  as 
would  be  required  to  combine  with  the  phosphoric  acid — and  then 
add  to  the  solution  75  c.  c.  of  water  and  90  c.  c.  of  ammonia  solu- 
tion of  sp.  gr.  0-96.  The  precipitate  should  be  distinctly  crystal- 
line ;  a  flocculent  precipitate  indicates  that  insufficient  ammonium 
citrate  has  been  added. 

Stir  vigorously  and  repeatedly  and  after  12  hours  filter,  wash 
with  dilute  ammonia,  ignite  and  weigh.  The  use  of  GOOCH'S  as- 
bestus  filter  greatly  facilitates  the  work. 

5.  Reverted  Phosphoric  Acid.     Place  2  grm.  of  substance  in 
a  mortar.     Take  100  c.  c.  of  neutral  or  slight  alkaline  ammonium 
citrate  solution,  sp.  gr.  1.09,  (the  commercial   citrate  is   strongly 
acid),  pour  50  c.  c.  on  the  substance,  add  dilute  ammonia  to  slight 
alkaline  reaction,  pulverize  the  substance,  let  the  coarser  parts  settle, 
pour  off  the  turbid  liquid  into  a  flask,  grind  the  residue  to  the 
finest  powder  and  wash  it  with  the  remaining  citrate  solution  into 
the  flask,  keep  the  contents  of  the  latter  at  30° — 40°  for  half  an 
hour,  with  very  frequent  shaking,  then  dilute  to  200  c.  c.,  pour 
upon  a  dry  filter,  take  100  c.  c.  of  filtrate =1  grm.  substance,  add  40 
c.  c.  magnesia  mixture,  120  c.  c.  water  and  100  c.  c.  ammonia,  stir, 
filter,  ignite,  etc.,  as  under  4. 

Deducting  the  soluble  phosphoric  acid  from  that  here  found 
gives  the  amount  of  "  reverted  phosphoric  acid" 

6.  Insoluble  Phosphoric  Acid.      5  grm.  of  the  superphosphate 
are  wet  with  5  c.  c.  solution  of  magnesium  nitrate,  sp.  gr.  1.3554 


*  Neutralize  185  grm.  citric  acid  with  ammonia  or  ammonium  carbonate,  in 
very  slight  excess,  and  bring  to  a  volume  of  1000  c.  c. 

f  HO  grm.  crystallized  MgCl26H2O,  140  grm.  NH4C1,  700  c.  c.  solution  of 
ammonia  sp.  gr.  0'96,  and  water  to  make  2  litres.  Instead  of  MgCl26H2O,  22 
grm.  of  calcined  magnesia  may  be  dissolved  in  the  equivalent  quantity  of  HC1, 
the  solution  boiled  with  a  little  calcined  magnesia  in  excess  and  filtered. 

\  Dissolve  160  grm.  calcined  MgO  in  the  equivalent  quantity  of  HNO3,  boil 
with  a  little  excess  of  MgO,  filter  and  bring  to  volume  of  1  litre.  5  c.  c.  of  this 
solution  is  enough  to  prevent  formation  of  pyrophosphate  in  5  grm.  of  any  com- 
mercial superphosphate.  If  not  enough  to  destroy  organic  matters,  moisten  the 
residue  of  ignition  with  HNOs  and  heat  again. 


§220.]  ANALYSIS    OF   COMMERCIAL   FERTILIZERS.  769 

evaporated  tp  dryness  and  gently  ignited.  The  residue  is  digested 
with  hydrochloric  acid,  diluted  to  500  c.  c.  and  filtered  on  a  dry 
filter.  To  100  c.  c.  of  filtrate  (=  1  grm.  substance)  are  added 
4»>  c.  c.  ammonium  citrate  solution,  25  c.  c.  magnesium  mixture, 
lUU  c.  c.  water  and  90  c.  c.  ammonia.  The  precipitate  is  treated 
as  under  4.  Subtracting  the  result  of  5  from  that  of  6,  gives  the 
"  insoluble  phosphoric  acid." 

7.  To  apply  the  molybdic  method  to  the  analysis  of  superphos- 
phates, determine  total  phosphoric  acid  in  2  grm.,  first  ignited  with 
addition  of  magnesium  nitrate,  then   treated  with  nitric  acid  to 
complete   solution    of   the    phosphates    and    diluted   to    500  c.  c. 
lot i  c,  c.  of  this  solution  are  used.     Determine  "insoluble  phos- 
phoric acid "   in  a  suitable  aliquot  of  the   nitric  solution  of  the 
insoluble  residue  of  5.   Reverted  phosphoric  acid  is  found  indirectly 
by  subtracting  from  the  total  the  sum  of  the  soluble  and  insoluble. 

8.  Potash.     Boil  10  grin,  with  water  for  10  minutes,  dilute  the 
solution  to  1000  c.c.  and  filter  through  a  dry  filter. 

The  error  of  measurement  due  to  the  presence  of  undissolved 
matters  is  inconsiderable  and  may  be  neglected.  Heat  100  c.c.  of 
the  filtrate  to  boiling,  precipitate  sulphuric  acid  by  barium  chloride 
and  magnesium  iron,  &c.,  together  with  phosphoric  acid  by  barium 
hydroxide  and  filter.  In  the  filtrate,  heated  nearly  to  boiling,  pre- 
cipitate the  barium  by  ammonium  carbonate  and  filter.  Evaporate 
the  filtrate  to  dryness,  expel  ammonium  salts  by  ignition,  dissolve 
the  residue  in  a  little  water  and  determine  the  potash  by  excess  of 
platinic  chloride  in  the  usual  way. 

When  the  substance  contains  much  soluble  organic  matters  it  is 
better  to  destroy  these  at  the  outset  by  heat,  which  should  be  very 
gentle  at  first  and  may  finally  reach  faint  redness. 

Nitrogen  may  exist  in  superphosphates  either  in  organic  com- 
bination, as  ammonium  salts,  or  as  nitrates. 

9.  The  nitrogen  of  ammonium  salts  is  determined  in  all  cases 
by  distilling  with   calcined  magnesia — proceeding  as  directed  p. 
220,  except  that  magnesia  must  be  used  instead  of  potash  or  lime. 

10.  The  nitrogen  in  organic  combination  when  alone  or  together 
with  ammonium  salts  is  determined  by  combustion  with  soda  lime 
(p.     644),    in   the    latter   case   subtracting    from    the   result    the 
amount  of  nitrogen  already  found  to  exist  in  ammonium  salts. 

11.  Nitrogen  in  the  form  of  nitrates  is  determined  by  SCHULZE'S 
method  as  described  on  p.  473. 


770  SPECIAL  PART.  [§  220. 

12.  "When    nitrates    and    nitrogenous   organic  matters   occur 
together,  it  is  necessary  to  determine  the  total  nitrogen  by  the 
absolute  method  as  described  on  p.  63755. 

The  determination  of  soluble,  reverted,  and  insoluble  phosphoric 
acid,  of  potash  and  of  nitrogen,  is  usually  sufficient  to  fix  the  com- 
mercial value  of  a  superphosphate.  It  is  sometimes  required,  how- 
ever, to  determine  water,  sulphuric  acid  and  chlorine. 

13.  Water.     Dry  one  gramme  for  three  hours  at  100°.     It  is 
often  impracticable,  and  for  commercial  purposes  is  unnecessary, 
to  make  an  accurate  water  determination.     Gypsum,  which  most 
superphosphates   contain  in  considerable  quantity,  does  not  part 
with  all  its  water  readily  or  completely  at  100°,  while  a  higher  heat 
to  some  extent  decomposes  the  organic  matters. 

14.  Sulphuric   acid.     Boil   one   grm.  with   water   acidulated 
with  hydrochloric  acid,  filter,  and  determine  sulphuric  acid  in  the 
filtrate  in  the  usual  way.     It  is  advisable  in  all  cases  to  purify  the 
precipitate  as  described  on  p.  366. 

15.  Chlorine  is  estimated  by  YOLHAKD'S  method,  or  by  precipi- 
tation with  silver  nitrate,  in  the  clear  hot  water  extract  of  1  grm. 

GUANO. 

16.  The  determinations  of  phosphoric  acid,  soluble,  "reverted," 
and  insoluble,  are  made  precisely  as  in  the  case  of  a  superphos- 
phate.    The  soluble  phosphoric  acid  consists  of  phosphates  of  the 
alkalies,  and  the  washings,  except  in  the  case  of  "  rectified"  guanos 
which  have  been  treated  with  oil  of  vitriol,  are  alkaline. 

17.  Determine  nitrogen  as  in  superphosphates.     Many  guanos 
contain  ammonium  carbonate  and  therefore  require  care  in  manipula- 
tion to  prevent  its  escape.     If  nitrates  are  present,  add  to  the  0-5 
gr.  taken  for  combustion  with  soda  lime  an  equal  weight  of  pure 
sugar  or  oxalic  acid.     The  quantity  of  nitrate  is  so  small  that  with 
this  precaution  accurate  results  are  obtained  without  resorting  to 
the  absolute  method. 

18.  Potash  is  determined  as  in  superphosphates. 

19.  If  a  determination  of  water  is  required,  weigh  the  guano  in 
a  boat  and  introduce  it  into  a  tube  which  is  heated  to  100°  in  an 
air  or  water  bath.     One  end  of  this  tube  is  connected  with  a  dry- 
ing apparatus  containing  oil  of  vitriol  or  calcium  chloride.     The 
other  is  provided  with  a  U-tube  and  standard  acid  for  receiving 


§  220.]          ANALYSIS    OF    COMMERCIAL    FERTILIZERS.  771 

ammonia,  and  an  aspirator  to  maintain  a  current  of  dry  air.  The 
volatilized  ammonia  is  measured  with  a  standard  alkali  and  taken 
into  account  in  reckoning  the  loss  of  weight. 

BONE. 

20.  Water.     Dry  1  grm.  at  100°,  and  determine  water  by  loss. 

21.  Fat.     Transfer  the  dry  bone  to  an  extraction  apparatus  and 
extract  with  absolute  ether  as  long  as  anything  is  removed. 

Evaporate  the  ether  extract,  dry  at  100°  for  two  hours  and 
weigh. 

22.  Carbonic  acid.     Determine  carbonic  acid  in  1  grm.  by  the 
method  described  on  p.  4120. 

23.  Ash.     Incinerate  1  grm.  till  the  ash  is  white  or  light  gray. 
Moisten  with  ammonium  carbonate  solution,  dry,  ignite  gently  and 
weigh. 

24-.  Phosphoric  acid.  Dissolve  the  ash,  prepared  as  above,  in 
hydrochloric  acid,  filter,  dilute  to  250-300  c.c.,  add  12-15  grm.  of 
citric  acid  as  ammonium  citrate  and  precipitate  with  magnesia 
mixture  in  the  manner  previously  described,  4,  or  dissolve  in 
nitric  acid  and  proceed  by  the  molybdic  process. 

25.  Nitrogen.     Determine   nitrogen  in  1  grm.  by  combustion 
with  soda  lime. 

For  most  purposes  the  determination  of  phosphoric  acid  and 
nitrogen  in  sufficient. 

POTASH  SALTS. 

26.  Boil  5  grm.  with  water  for  10  minutes,  dilute  to  1000  c.c. 
and  determine  potash  in  100  c.c.  as  described  under  8  or  29. 

27.  In  another  portion  of  100  c.c.,  determine  sulphuric  acid  by 
barium  chloride,  and  in  a  third  portion  chlorine  may  be  deter- 
mined by  precipitation  with  silver  nitrate,  or  more  conveniently 
by  VOLHARD'S  method. 

28.  Determine  water  by  heating  2-5  grm.  in  a  platinum  capsule 
to  dull  redness. 

29.  Potash.     STOHMANN  directs  to   boil  10  grm.  of  substance 
with  about  300  c.c.  of  water,  and  to  add  dropwise  BaCl2  solution 
until  no  further  precipitate  appears,  to  let  cool  and  dilute  to  1000 
c.c.,  and  after  subsidence  or  filtration  to  take  100  c.c.  of  the  clear 
solution,  add  a  large  excess  of  PtCl4  (equivalent  to  about  2  grm. 


772  SPECIAL  PART.  [§  222. 

Pt),  evaporate  and  proceed  as  usual  with  the  precipitate.  As  the 
alkali-earth  platinchlorides  are  all  soluble  in  alcohol,  the  results  are 
good. 

21.    ANALYSIS   OF  ATMOSPHEETC  AIE. 
§221. 

In  the  analysis  of  atmospheric  air  we  usually  confine  our  at- 
tention to  the  following  constituents :  oxygen,  nitrogen,  carbonic 
acid,  and  aqueous  vapor.  It  is  only  in  exceptional  cases  that  the 
exceedingly  minute  quantities  of  ammonia  and  other  gases— many 
of  which  may  be  assumed  to  be  always  present  in  infinitesimal 
traces — are  also  determined. 

It  does  not  come  within  the  scope  of  the  present  work  to  de- 
scribe all  the  methods  which  have  been  employed  in  the  capital 
investigations  made  in  the  last  few  years  by  BRUNNER,  BUNSEN, 
DUMAS  and  BOUSSINGAULT,  REGNAULT  and  REISET,  and  others.  To 
these  methods  we  are  indebted  for  a  more  accurate  knowledge  of 
the  composition  of  our  atmosphere,  and  excellent  descriptions  of 
them  will  be  found  in  the  works  below.* 

I  confine  myself  to  those  methods  which  are  found  most  con- 
venient in  the  analysis  of  the  air  for  medical  or  technical  purposes. 

A.   DETERMINATION  OF  THE  WATER  AND  CARBONIC  ACID. 

§222. 

It  was  formerly  the  custom  to  effect  these  determinations  by 
BRUNNER'S  method,  which  consisted  iii  slowly  drawing,  by  means 
of  an  aspirator,  a  measured  volume  of  air  through  accurately 
weighed  apparatuses  filled  with  substances  having  the  property 
of  retaining  the  aqueous  vapor  and  the  .carbonic  acid,  and  esti- 
mating these  two  constituents  by  the  increased  weights  of  the  ap- 
paratuses. 

Fig.  103  represents  the  arrangement  recommended  by  REG- 
NAULT. 

*Ausfiihrliches  Handbuch  der  analytischen  Chemie,  von  H.  Rose,  II.  853; 
Graham-Otto's  Ausf  uhrliches  Lehrbuch  der  Chemie,  Bd.  II.  Abth.  1,  S.  102  et  seq.; 
Handworterbuch  der  Chemie,  von  Liebig,  Poggendorff  und  Wohler,  2  Aufl.  Bd, 
II.  S.  431  et  seq.;  and  Bunsen's  Gasometry. 


§  222.]  ANALYSIS   OF  ATMOSPHERIC    AIR.  773 

The  vessel  V  is  made  of  galvanized  iron,  or  of  sheet  zinc ;  it 
holds  from  50  to  100  litres,  and  stands  upon  a  strong  tripod  in  a 
trough  large  enough  to  hold  the  whole  of  the  water  that  V  con- 
tains. At  a  a  brass  tube,  c,  with  stopcock,  is  firmly  fixed  in  with 
cement.  Into  the  aperture  &,  which  serves  also  to  fill  the  appara- 
tus, a  thermometer  reaching  down  to  the  middle  of  V  is  fixed  air- 
tight by  means  of  a  perforated  cork  soaked  in  wax. 

The  efflux  tube,  7',  which  is  provided  with  a  cock,  is  bent  slightly 
upward,  to  guard  against  the  least  chance  of  air  entering  the  vessel 


Fig.  103. 

from  below.  The  capacity  of  the  vessel  is  ascertained  by  filling  it 
completely  with  water,  and  then  accurately  measuring  the  contents 
in  graduated  vessels.  The  end  of  the  tube  c  is  connected  air-tight 
with  F,  by  means  of  a  caoutchouc  tube ;  the  tubes  A — F  are  simi- 
larly connected  with  one  another.  J.,  -B,  E,  and  F  are  filled  with 
small  pieces  of  glass  moistened  with  pure  concentrated  sulphuric 
acid,  C  and  D  with  moist  slaked  lime.*  Finally,  A  is  also  con- 


*  With  regard  to  C  and  Z>,  I  have  returned  to  lime,  preferring  it  to  purnice 
saturated  with  solution  of  potash,  because,  as  Hlasiwetz  (Chem.  Centralbl.  1856, 
575)  has  shown,  the  solution  of  potash  absorbs  not  only  carbonic  acid,  but  also 
oxygen.  Indeed,  H.  Rose  had  previously  made  a  similar  observation.  With  re- 
spect to  the  other  tubes,  I  prefer  the  concentrated  sulphuric  acid  to  calcium 
chloride  as  the  absorbent  for  water  (see  Pettenkofer,  Sitzungsber.  der  bayer 


774  SPECIAL   PART.  [§  222. 

nected  with  a  long  tube  leading  to  tlie  place  from  which  the  air 
intended  for  analysis  is  to  be  taken.  The  corks  of  the  tubes  are 
coated  over  with  sealing-wax.  The  tubes  A  and  B  are  intended 
to  withdraw  the  moisture  from  the  air ;  they  are  weighed  together. 
C,  D,  and  E  are  also  weighed  jointly.  C  and  D  absorb  the  car- 
bonic acid ;  E  the  aqueous  vapor  which  may  have  been  withdrawn 
from  the  hydrate  of  lime  by  the  dry  air.  F  need  not  be  weighed ; 
it  simply  serves  to  protect  E  against  the  entrance  of  aqueous  vapor 
from  V. 

The  aspirator  is  completely  filled  with  water ;  c  is  then  con- 
nected with.  F,  and  thus  with  the  entire  system  of  tubes ;  the  cock 
r  is  opened  a  little,  just  sufficiently  to  cause  a  slow  efflux  of  water. 
As  the  height  of  the  column  of  water  in  V  is  continually  dimiii- 
•ishing,  the  cock  must  from  time  to  time  be  opened  a  little  wider, 
to  maintain  as  nearly  as  possible  a  uniform  flow  of  water.  "When 
V  is  completely  emptied,  the  height  of  the  thermometer  and  that 
of  the  barometer  are  noted,  and  the  tubes  A  and  B,  and  (7,  Z>,  and 
^weighed  again. 

As  the  increase  of  weight  of  A  and  B  gives  the  amount  of 
water,  that  of  C,  D,  and  E  the  amount  of  carbonic  acid,  in  the  air 
which  has  passed  through  them ;  and  as  the  volume  of  the  latter 
(freed  from  water  and  carbonic  acid)  is  accurately  known  from  the 
ascertained  capacity  of  V*  the  calculation  is  in  itself  very  simple ; 
but  it  involves,  at  least  in  very  accurate  analyses,  the  following 
corrections : — 

of.  Reduction  of  the  air  in  I7",  which  is  saturated  with  aqueous 
vapor,  to  dry  air ;  since  the  air  which  penetrates  through  c  is  dry. 

/?.  Reduction  of  the  volume  of  dry  air  so  found  to  0°,  and 
Y60  mm. 

When  these  calculations  have  been  made  (see  "  Calculations  of 
Analyses,"  in  Appendix),  the  weight  of  the  air  which  has  pene- 
trated into  F  is  readily  found  from  the  datum  in  Table  Y.  at  the 

Akad.  1862,  II.  Heft  1,  S.  59).  Hlasiwetz's  statement,  that  concentrated  sul- 
phuric acid  also  takes  up  carbonic  acid,  I  nave  found  to  be  unwarranted. 
Calcium  chloride  does  not  dry  the  air  completely,  and,  besides,  Hlasiwetz  says 
that  when  it  is  used  a  trace  of  chlorine  is  carried  away  corresponding  to  tne 
amount  of  ozone  in  the  air  (op.  cit.  p.  517). 

*  Or  from  the  quantity  of  water  which  has  flown  from  V,  as  the  experiment 
may  be  altered  in  this  way,  that  a  portion  only  of  the  water  is  allowed  to  run 
out,  and  received  in  a  measuring  vessel. 


g  2*22.]  ANALYSIS    OF    ATMOSPHERIC    AIR.  77.") 

end  of  the  volume;  and  as  the  carbonic  acid  and  water  have  also 
been  weighed,  the  respective  quantities  of  these  constituents  of  the 
air  may  now  be  expressed  in  per  cents,  by  weight,  or,  calculating 
the  weights  into  volumes,  in  per  cents,  by  measure. 

Considering  the  great  weight  and  size  of  the  absorption  appara- 
tus, in  comparison  to  the  increase  of  weight  by  the  process,  at  least 
25,000  c.  c.  of  air  must  be  passed  through ;  the  air  inside  the  bal- 
ance-case must  be  kept  as  dry  as  possible  by  means  of  a  sufficient 
quantity  of  calcium  chloride,  and  the  apparatus  left  for  some  time 
in  the  balance-case  before  proceeding  to  weigh.  Neglect  of  these 
measures  would  lead  to  considerable  errors,  more  particularly  as 
regards  the  carbonic  acid,  the  quantity  of  which  in  atmospheric  air 
is,  on  an  average,  about  10  times  less  than  that  of  the  aqueous  vapor 
(comp.  HLASIWETZ,  loc.  cit.}. 

For  the  exact  determination  of  the  carbonic  acid  one  of  the  fol- 
lowing methods  is  far  better  suited  : — 

a.  Process  suggested  by  FK.  MOHR,  applied  and  carefully  tested 
l}ij  H.  v.  GILM."*  VON  GILM  employed  in  his  experiments  an  aspira- 
tor holding  at  least  30  litres,  which  was  arranged  like  that  shown 
in  fig.  103,  but  had  a  third  aperture,  bearing  a  small  manometer. 
The  air  was  drawn  through  a  tube,  1  metre  long  and  about  15  mm. 
wide ;  this  tube  wras  drawn  out  thin  at  the  upper  end,  and  at  the 
lower  end  bent  at  an  angle  of  140° — 150°.  It  was  more  than 
half  filled  with  coarse  fragments  of  glass  and  perfectly  clear  baryta 
water,  and  fixed  in  such  a  position  that  the  long  part  of  it  was 
inclined  at  an  angle  of  8° — 10°  to  the  horizontal.  A  narrow  glass 
tube,  fitted  into  the  undrawn-out  end  of  the  tube  by  means  of  a 
cork,  served  to  admit  the  air.  Two  small  flasks,  filled  with  baryta 
water,  were  placed  between  the  absorption  tube  and  the  aspirator ; 
these  were  intended  as  a  control,  to  show  that  the  whole  of  the 
carbonic  acid  had  been  retained.  When  about  60  litres  of  air  had 
slowly  passed  through  the  absorption  tube,  the  barium  carbon- 
ate formed  was  filtered  oft'  out  of  contact  of  air,  and  the  tube  as 
well  as  the  contents  of  the  filter  washed,  first  with  distilled  water 
saturated  with  barium  carbonate,  then  with  pure  boiled  water. 
The  barium  carbonate  in  the  filter  and  in  the  tube  was  then  dis- 
solved in  dilute  hydrochloric  acid,  the  solution  evaporated  to  dry- 

*  Chem.  Centralbl.  1857,  760. 


776 


SPECIAL   PART. 


[§  222. 


Fig.  104. 


ness,  the  residue  gently  ignited,  and  the  chlorine  of  the  barium 
chloride  determined  as  directed  §  141,  5,  a.  2  atoms  of  chlorine 
represent  1  mol.  carbonic  acid.  It  is  obvious  that  one  may  also 
determine  the  barium  in  the  hydrochloric  acid  solution  by  precipi- 
tating with  sulphuric  acid.  For  filtering  the  barium  carbonate, 
v.  GILM  employed  a  double  funnel  (fig.  104) ;  the  inner  cork  has, 
besides  the  perforation  through  which  the  neck  of  the  funnel 
passes,  a  lateral  slit,  which  establishes  a  commu- 
nication between  the  air  in  the  outer  funnel  and 
the  air  in  the  bottle. 

As,  with  the  absorption  apparatus  arranged 
as  described,  the  air  has  to  force  its  way  through 
a  column  of  fluid,  the  manometer  is  required  to  de- 
termine the  actual  volume  of  the  air ;  the  height 
indicated  by  this  instrument  being  deducted  from 
the  barometric  pressure  observed  during  the  pro- 
cess. 

FR.  MOHR  *  now  recommends  as  the  absorb- 
ent fluid  a  solution  of  barium  hydroxide  in  pot- 
ash. -This  is  prepared  by  dissolving  crystals  of  barium  hydroxide 
in  weak  solution  of  potash  with  the  aid  of  heat,  and  filtering  off 
the  barium  carbonate,  which  invariably  forms  in  small  quantity. 
The  clear  filtrate  is  accordingly  saturated  with  barium  carbonate. 
MOHR  now  leaves  out  the  fragments  of  glass. 

This  method  afforded  v.  GILM  very  harmonious  results.  Nev- 
ertheless, it  involves  one  source  of  error.  If  clear  baryta  water  is 
passed  through  paper  with  the  most  careful  possible  exclusion  of 
air,  and  the  filter  is  washed  till  the  washings  are  free  from  baryta, 
and  dilute  hydrochloric  acid  is  then  poured  upon  the  filter,  and  the 
filtrate  thus  obtained  is  evaporated,  a  small  quantity  of  barium 
chloride  will  be  left,  showing  that  a  little  baryta  was  kept  back  by 
the  paper.  AL.  MULLER  f  has  already  called  attention  to  the  capa- 
city of  filter  paper  for  retaining  baryta. 

1).  M.  PETTENKOFER'S  process. \ 

a.  Principle  and  Requisites.     A  known  volume  of  air  is  made 

*  Lehrbuch  der  Titrirmethode,  2d  ed.  446. 
•f  Journ.  f.  prakt.  Chem.  83,  384. 

\  Abhandl.  der  naturw.  u.  tcchn.  Commission  der  k.  bayer.  Akad.  der  Wiss. 
II.  1;  Annul,  d.  Chem.  u.  Pharm.  II.  Supplem.  Bd.  p.  1. 


§  222.]  ANALYSIS   OF   ATMOSPHERIC   AIE.  777 

to  act  upon  a  definite  quantity  of  standard  baryta  water  (standard- 
ized by  oxalic  acid  solution),  in  such  manner  that  the  carbonic  acid 
is  completely  bound  by  the  baryta.  The  baryta  water  is  then 
poured  out  into  a  cylinder,  and  allowed  to  deposit  with  exclusion 
of  air,  a  part  of  the  clear  fluid  is  then  removed,  and  the  baryta 
remaining  in  solution  is  determined.  The  difference  between  the 
oxalic  acid  required  for  a  certain  quantity  of  baryta  water  before 
and  after  the  action  of  the  air  represents  the  barium  carbonate 
formed,  and  consequently  the  carbonic  acid  present. 

Two  kinds  of  baryta  water  are  used:  one  contains  21  grm.  and 
the  other  7  grm.  crystallized  barium  hydroxide  *  in  the  litre  ;  these 
serve  for  the  determination  of  larger  and  smaller  quantities  of  car- 
bonic acid  respectively.  1  c.  c.  of  the  stronger  corresponds  to 
about  3  ingrm.  carbonic  acid,  of  the  weaker  1  c.  c.  corresponds  to 
about  1  mgrm.f 

The  oxalic  acid  solution  which  serves  for  standardizing  the 
baryta  water  contains  2'8636  grm.  cryst.  oxalic  acid  in  1  litre. 
1  c.  c.  corresponds  to  1  mgrm.  carbonic  acid.  The  baryta  water  is 
standardized  as  follows: — Transfer  30  c.  c.  of  it  to  a  flask,  and  then 
run  in  the  oxalic  acid  from  a  MOHR'S  burette  with  float ;  shake 
the  fluid  from  time  to  time,  closing  the  mouth  of  the  flask  with 
the  thumb.  The  vanishing  point  of  the  alkaline  reaction  is  ascer- 

*  The  barium  hydroxide  must  be  entirely  free  from  caustic  potash,  and  soda, 
the  smallest  quantities  of  which  render  the  volumetric  estimation  in  the  presence 
of  barium  carbonate  impossible,  since  the  normal  alkali  oxalates  decompose  the 
alkali-earth  carbonates.  When  a  trace  even  of  barium  carbonate  is  suspended 
in  the  fluid — and  this  is  always  the  case  when  a  baryta  water  which  has  been 
used  for  the  absorption  of  carbonic  acid  is  not  filtered — the  reaction  continues 
alkaline  if  the  smallest  trace  of  potash  or  soda  is  present,  because  the  alkali  oxa- 
late  formed  immediately  enters  into  decomposition  with  the  barium  carbonate. 
A  fresh  addition  of  oxalic  acid  converts  the  alkali  carbonate  again  into  oxalate. 
and  the  fluid  is  for  a  moment  neutral,  till,  on  shaking  with  air,  the  carbonic  acid 
escapes,  and  any  barium  carbonate  still  present  converts  the  alkali  oxalate  again 
into  carbonate.  To  test  a  baryta  water  for  caustic  alkali,  determine  the  alkalin- 
ity of  a  perfectly  clear  portion,  and  then  of  a  portion  that  has  been  mixed  with  a 
little  pure  precipitated  barium  carbonate.  If  you  use  more  oxalic  acid  in  the 
second  than  in  the  first  experiment,  caustic  alkali  is  present,  and  some  barium 
chloride  must  be  added  to  the  baryta  water  before  it  can  be  used. 

f  [The  baryta  water  is  kept  in  a  bottle  under  a  thin  stratum  of  kerosene 
(MOHR).  It  is  drawn  off  through  a  siphon  supported  in  the  stopper,  the  outer 
leg  of  which  is  recurved  upwards  and  closed  with  a  bit  of  rubber  tube  and  clip. 
By  having  this  leg  of  the  siphon  sufficiently  long  the  burette  may  be  filled  by 
inserting  its  delivery  end  in  the  rubber  tube  and  opening  both  clips.] 


778  SPECIAL    PART.  [§222. 

tained  with  delicate  turmeric  paper.  *  As  soon  as  a  drop  of  the 
fluid  placed  on  the  paper  does  not  give  a  brown  ring,  the  end  is 
attained.  If  you  were  obliged,  in  the  first  experiment,  to  take 
out  too  many  drops  for  testing  with  turmeric  paper,  consider  the 
result  as  only  approximate,  and  make  a  second  experiment,  adding 
at  once  the  whole  quantity  of  oxalic  acid  to  within  1  or  ^  c.  c.  and 
then  beginning  to  test  with  paper.  A  third  experiment  would  be 
found  to  agree  with  the  second  to  ^  c.  c.  The  reaction  is  so  sen- 
sitive that  all  foreign  alkaline  matter,  particles  of  ash,  tobacco 
smoke,  &c.,  must  be  carefully  guarded  against. 

/3.  The  actual  Analysis.  This  may  be  effected  in  two  differ- 
ent ways. 

aa.  Take  a  perfectly  dry  bottle,  of  about  6  litres  capacity,  with 
well-fitting  ground  glass  stopper,  and  accurately  determine  the 
capacity ;  fill  the  bottle,  by  means  of  a  pair  of  bellows,  with  the 
air  to  be  analyzed ;  add  45  c.  c.  of  the  dilute  standard  baryta  wrater, 
and  cause  the  baryta  water  to  spread  over  the  inner  surface  of  the 
bottle  by  turning  the  latter  about,  but  without  much  shaking.  In  the 
course  of  about  -J  an  hour  the  whole  of  the  carbonic  acid  is  absorbed. 
Pour  the  turbid  baryta  water  into  a  cylinder,  close  securely,  and 
allow  to  deposit ;  then  take  out,  by  means  of  a  pipette,  30  c.  c.  of 
the  clear  supernatant  fluid,  run  in  standard  oxalic  acid,  multiply 
the  volume  used  by  1*5  (as  only  30  c.  c.  of  the  original  45  are  em- 
ployed in  this  experiment),  and  deduct  the  product  from  the  c.  c. 
of  oxalic  acid  used  for  45  c.  c.  of  the  fresh  baryta  water;  the  dif- 
ference represents  the  quantity  of  baryta  converted  into  carbonate, 
and  consequently  the  amount  of  the  carbonic  acid.  If  the  air  is 
unusually  rich  in  carbonic  acid,  the  concentrated  baryta  water  is 
employed. 

bb.  Pass  the  air  through  a  tube  or  through  two  tubes  contain- 
ing measured  quantities  of  standard  baryta  water  and  finish  the 
experiment  as  in  aa.  For  passing  a  definite  quantity  of  air  we 
should  generally  employ  an.  aspirator  (p.  7Y3)  ;  PETTENKOFER  in  his 
experiments  with  the  respiration  apparatus  forced  the  air  by  means 
of  small  mercurial  pumps  first  through  the  tubes,  and  then  through 
an  apparatus  for  measuring  the  gas.  The  form  and  arrangement 


*  Prepared  with  lime-free  Swedish  filter  paper  and  tincture  of  turmeric.  The 
spirit  used  in  making  the  latter  must  be  free  from  acid.  Dry  the  paper  in  a  dark 
room,  and  keep  it  protected  from  the  light.  It  is  lemon  yellow. 


§  223.]  ANALYSIS    OF    ATMOSPHERIC    AIU.  779 

of  the  tubes  is  illustrated  by  tig.  105.  Two  such  tubes  were  used ; 
the  first  was  1  metre,  the  second  '3  metres  long ;  they  were  filled 
with  baryta  water — the  former  with  the  stronger  solution,  the  lat- 
ter with  the  weaker.  The  air  is  introduced  through  the  short 
limbs  of  the  tubes,  and  the  glass  tubes  themselves  are  so  inclined 


Fig.  105. 

that  the  bubbles  of  air  move  on  with  the  necessary  rapidity  with- 
out uniting.  The  motion  of  the  gas  bubbles  keeps  up  a  constant 
mixing  of  the  baryta  water. 


B.    DETERMINATION  OF  THE  OXYGEN  AND  NITROGEN. 
§223. 

The  method  I  shall  give  is  that  proposed  by  v.  LIEBIG.*  It  is 
based  upon  the  observation  made  by  CHEVREUL  and  DOBEREINER, 
that  pyrogallic  acid,  in  alkaline  solutions,  has  a  powerful  tendency 
to  absorb  oxygen. 

1.  A  strong  measuring  tube,  holding  30  c.  c.  and  divided  into 
^  or  yL  c.  c.,  is  filled  to  f  with  the  air  intended  for  analysis.     The 
remaining  part  of  the  tube  is  filled  with  mercury,  and  the  tube  is 
inverted  over  that  fluid  in  a  tall  cylinder,  widened  at  the  top. 

2.  The  volume  of  air  confined  is  measured  (§  12).      If  it  is 
intended  to  determine  the  carbonic  acid — which  can  be  done  with 
sufficient  accuracy  only  if  the  quantity   of  the  acid  amounts  to 
several  per  cents. — the  air  is  dried  by  the  introduction  of  a  ball  of  cal- 
cium chloride  before  measuring.    If  it  is  not  intended  to  determine 


Annal.  d.  Chem.  u.  Pharm.  77,  107. 


780  SPECIAL    PART.  [§  223. 

the  carbonic  acid  this  operation  is  omitted.    A  quantity  of  solution  of 
potassa  of  1*4  sp.  gr.  (1  part  of  dry  potassium  hydroxide  to  2 
parts  of  water),  amounting  to  from  ^  to  ^  of  the  volume 
of  the  air,  is  then  introduced  into  the  measuring  tube  by 
means  of  a  pipette  with  the  point  bent  upwards  (fig.  106), 
and  spread  over  the  entire  inner  surface  of  the  tube  by  shak- 
ing the  latter ;  when  no  further  diminution  of  volume  takes 
place,  the  decrease  is  read  off.     If  the  air  has  been  dried 
Fig.  106.  previously  with  calcium  chloride,  the  diminution  of  the 
volume  expresses  exactly  the  amount  of  carbonic  acid  con- 
tained in  the  air ;  but  if  it  has  not  been  dried  with  calcium  chloride, 
the  diminution  in  the  volume  cannot  afford  correct  information  as 
to  the  amount  of  the  carbonic  acid,  since  the  strong  solution  of 
potassa  absorbs  aqueous  vapor. 

3.  "When  the  carbonic  acid  has  been  removed,  a  solution  of 
pyrogallic  acid,  containing  1  grm.  of  the  acid*  in  5  or  6  c.  c.  of 
water,  is  introduced  into  the  same  measuring  tube  by  means  of 
another  pipette,  similar  to   the   one   used   in    2  (fig.  106) ;    the 
quantity  of  pyrogallic  acid  employed  should  be  half  the  volume  of 
the  solution  of  potassa  used  in  2.     The  mixed  fluid  (the  pyrogallic 
acid  and  solution  of  potassa)  is  spread  over  the  inner  surface  of  the 
tube  by  shaking  the  latter,  and,  when  no  further  diminution  of 
volume  is  observed,  the  residuary  nitrogen  is  measured. 

4.  The  solution  of  pyrogallic  acid  mixing  with  the  solution  of 
potassa  of  course  dilutes  it,  causing  thus  an  error  from  the  diminu- 
tion of  its  tension ;  but  this  error  is   so  trifling  that  it  has  no 
appreciable  influence  upon  the  results ;  it  may,  besides,  be  readily 
corrected,  by  introducing  into  the  tube,  after  the  absorption  of  the 
oxygen,  a  small  piece  of  hydrate  of  potassa  corresponding  to  the 
amount  of  water  in  the  solution  of  the  pyrogallic  acid. 

5.  There  is  another  source  of  error  in  this  method  ;  viz.,  on 
account  of  a  portion  of  the  fluid  always  adhering  to  the  inner  sur- 
face of  the  tube,  the  volume  of  the  gas  cannot  be  read  off  with 
absolute  accuracy.     In  comparative  analyses,  the  influence  of  this 
defect  upon  the  results  may  be   almost   entirely  neutralized,  by 
taking  nearly  equal  volumes  of  air  in  the  several  analyses.f 


*  Liebig  has  described  a  very  advantageous  method  of  preparing  pyrogallic 
acid.     See  Annal.  d.  Chem.  u.  Pharm.  101,  47. 

f  Bunsen  employs  for  the  absorption  of  oxygen  a  papier-mache  ball  saturated 


§  224.]  ARSENIC   IN    ORGANIC    MATTER.  781 

6.  Notwithstanding  these  sources  of  error,  the  results  obtained 
by  this  method  are  very  accurate  and  constant.  In  eleven 
analyses  which  v.  LIEBIG  reports,  the  greatest  difference  in  the 
amount  of  oxygen  found  was  between  20*75  and  21'03.  The  num- 
bers given  express  the  actual  and  uncorrected  results. 


[22.   DETECTION  AKD   ESTIMATION  OF  AKSEXIC  IX 
OBGAXIC  MATTER 


GAUTIER'S  Method  simplified  ty  JOHNSON  AND  CHITTENDEN. 

The  following  method  for  the  detection  and  estimation  of 
arsenic  in  organic  matter  is  a  modification  of  the  process  recently 
described  by  GAITTIER.*  GAUTIER'S  method  consists  in  treating  the 
substance  with  certain  quantities  of  nitric  acid,  and  afterwards  of 
sulphuric  acid,  at  a  high  temperature,  whereby  the  organic  matters 
are  partly  destroyed  and  converted  into  slightly  soluble  humus-like 
bodies,  from  which  all  the  arsenic  may  be  extracted  by  boiling 
water.  Gautier  treats  the  brown  'solution  thus  obtained  with 
"  sodium  bi-snlphate,  throws  down  the  arsenic  in  the  state  of  sul- 
phide, with  hydrogen  sulphide,  transforms  this  sulphide  into  arsenic 
acid  by  known  means,"  treats  the  solution  thus  obtained  in  the 
Marsh  Apparatus,  and  finally  weighs  the  arsenic  in  the  metallic 
state  as  below  described. 

JOHNSON  and  CHTITENDEN  dispense  with  the  use  of  all  reagents 
but  sulphuric  acid,  nitric  acid,  and  zinc  alloyed  with  a  little  pla- 
tinum, which  are  not  difficult  to  obtain  in  a  state  of  absolute  free- 
dom from  arsenic,  and  they,  together  with  DONALDSON,  have  dem- 
onstrated that  the  method,  thus  essentially  simplified,  gives  exact 
results.  The  following  account  of  the  process  is  from  a  paper  by 
CHITTENDEN  and  DoNALDSON.f 


with  a  concentrated  alkaline  solution  of  potassium  pyrogallate,  "which  he  intro- 
duces into  the  gaseous  mixture  attached  to  a  platinum  wire.  By  adopting  this 
proceeding  the  source  of  error  mentioned  in  5  is  avoided.  Bee  also  Russell, 
Jour.  Chem.  Soc.  1868,  pp.  130,  131. 

*  Bulletin  de  la  Societe  Chimique,  24,  250. 

f  American  Chemical  Journal,  vol.  ii.  p.  235. 


782 


SPECIAL   PAKT. 


I.  HEAGENTS  AND  APPARATUS. 

The  reagents  required  are  pure  granulated  zinc  alloyed  with  a 
small  quantity  of  platinum,  pure  concentrated  nitric  and  sulphuric 
acids,  and  three  dilute  sulphuric  acids  of  increasing  strength,  which, 
for  the  sake  of  convenience,  may  be  prepared  in  considerable  quan- 
tities. 


ISO  c.  c.  pure  cone.  II2SO4- 


-1000  c.  c.  H2O. 


Acid  No.  1. 

Acid  No*  2.     260  c.  c.  pure  cone.  1I2SO4+1000  c.  c.  H2O. 

Acid  No.  3.     425  c.  c.  pure  cone.  H2SO4+1000  c.  c.  H2O. 

The  form  of  MARSH  apparatus  used  is  shown  by  fig.  107. 

The  flask,  a  BUNSEN'S  wash-bottle  of  200  c.  c.  capacity,  is  pro- 


Fig.  107. 

vided  with  a  small  separating  funnel  of  65  c.  c.  capacity, 
with  glass  stopcock.  This  is  a  very  material  aid  to  the 
obtaining  of  a  slow  and  even  evolution  of  gas,  and  is  nearly 
indispensable  in  accurate  quantitative  work.  The  gas  generated 
is  dried  by  passing  through  a  calcium  chloride  tube,*  and  then 
passes  through  a  tube  of  hard  glass,  heated  to  a  red  heat  by  a  fur- 
nace of  three  BUNSEN  lamps  with  spread  burners,  so  that  a  contin- 
uous flame  of  six  inches  is  obtained,  and  with  a  proper  length  of 

*  OTTO  and  also  DRAGENDORFP  recommend  to  pass  the  gas  first  over  fragments 
of  caustic  potassa.  We  find,  however,  in  accordance  with  DOREMTJS,  that  arse, 
nic  is  arrested  by  caustic  alkali. — S.  W.  J.  and  R.  H.  C. 


§  224.]  AESENIC   IN   OEGANIC   31 ATTEE.  783 

cooled  tube  not  a  trace  of  arsenic  passes  by.  The  glass  tube  where 
heated  is  wound  with  a  strip  of  wire  gauze,  both  ends  being  sup- 
ported upon  the  edges  of  the  lamp  frame,  so  that  the  tube  does  not 
sink  down  when  heated.  The  small  furnace  is  provided  with  two 
appropriate  side  pieces  of  sheet  metal,  so  that  a  steady  flame  is 
always  obtained.  When  the  quantity  of  arsenic  is  very  small  the 
tube  is  naturally  so  placed  that  the  mirror  is  deposited  in  the  nar- 
row portion,  but  when  the  arsenic  is  present  to  the  extent  of  *005 
grin,  the  tube  should  be  6  millimetres  in  inner  diameter,  and  so 
arranged  that  fully  two  inches  of  this  large  tube  are  between  the 
flame  and  the  narrow  portion.  When  the  quantity  of  arsenic  is 
less  the  tube  can  naturally  be  smaller. 


II.  PROCESS. 

a.  Method  for  the  complete  extraction  of  arsenic  from  organic 
matter. 

100  grms  of  the  material  to  be  examined,  cut  into  small  pieces, 
are  placed  in  a  porcelain  casserole  of  600  c.  c.  capacity  and  provided 
with  a  stirring  rod  of  stout  glass.  23  c.  c.  of  pure  concentrated 
nitric  acid  are  added,  and  the  dish  placed  on  a  small  air-bath* 
provided  with  a  thermometer  and  a  single  BUXSEX  burner.  The 
m  ixture  is  then  heated  at  150° — 160°  C.,  with  occasional  stirring.  At 
first  the  tissue  takes  on  a  yellowish  color,  then  swells  up  somewhat, 
becoming  finally  quite  thick  ;  soon  changes  again,  becoming  liquid, 
and  then  generally  requires  heating  from  \\  to  2  hours,  the  tem- 
perature sometimes  being  raised  to  180°  C. 

At  this  point  the  mass,  being  now  quite  thick  again,  usually 
takes  on  a  deeper  yellow  color  or  orange  shade.  When  this  change 
of  color  is  noticed  the  casserole  is  taken  from  the  bath  and  3  c.  c.  of 
pure  concentrated  sulphuric  acid  added  and  the  mixture  stirred 
vigorously.  The  addition  of  concentrated  sulphuric  acid  to  the 
viscid  residue  rich  in  nitric  acid  and  nitro-com pounds  naturally 


*  For  air-bath  an  ordinary  flat-bottomed  tin  basin,  7  inches  in  diameter,  3 
inches  deep,  is  used  with  a  cover  provided  with  an  opening  5  inches  in  dia- 
meter. This  bath  is  set  in  an  iron  ring  fastened  to  a  stout  lamp-stand,  while  the 
end  of  the  thermometer  passes  through  a  small  hole  near  the  edge  of  the  cover  a 
short  distance  into  the  bath,  so  that  the  temperature  can  be  regulated. 


784  SPECIAL    PART.  [§  224. 

gives  rise,  especially  at  this  temperature,  to  a  considerable  com- 
motion: the  mass  becomes  brown,  swells  up,  nitrous  fumes  are 
copiously  evolved,  immediately  followed  by  dense  white  fumes  of 
suffocating  odor,  while  the  residue  in  the  dish  is  changed  either  into 
a  dry  carbonaceous  mass  or  a  black,  sticky,  tar-like  mass.  Although 
the  oxidation  is  so  powerful,  no  deflagration  takes  place,  and  the 
carbonization  is  effected  in  this  manner  without  the  volatilization 
of  any  arsenic.  The  casserole  is  again  placed  on  the  bath  and 
heated  for  a  few  minutes  at  180°  C.,  then,  while  still  on  the  bath, 
8  c.  c.  of  pure  concentrated  nitric  acid  are  added  drop  by  drop  with 
continual  stirring,  the  object  being  to  destroy  more  completely  the 
organic  matter,  arid  at  the  same  time  the  nitric  acid  falling  drop  by 
drop  on  the  carbonaceous  residue  tends  to  prevent  the  formation  of 
sulphurous  acid  and  the  consequent  formation  of  insoluble  arseni- 
ous  sulphide. 

After  the  addition  of  the  nitric  acid  the  dish  is  heated  at  200° 
C.  for  fifteen  minutes,  and  when  cold  a  hard  carbonaceous  residue 
is  the  result,  entirely  free  from  nitric  acid.  In  wror king  with  dif- 
ferent kinds  of  tissue,  slight  deviations  from  the  above  description 
will  frequently  be  observed.  When  much  bony  matter  is  present 
the  last  residue  takes  on  a  somewhat  different  character,  owing  to 
the  presence  of  calcium  sulphate,  and  occasionally  when  the  3  c.  c. 
of  sulphuric  acid  are  added  the  oxidation  does  not  at  once  take 
place,  but  requires  a  little  longer  heating  on  the  air-bath.  "When 
such  is  the  case  the  mixture  needs  constant  watching  in  order  to 
remove  the  dish  from  the  bath  at  the  first  approach  of  the  oxida- 
tion. 

The  arsenic  now  exists  as  arsenic  acid,  readily  soluble  in 
w^ater.  The  carbonaceous  residue  is  thoroughly  extracted  with 
boiling  water,  and  in  order  to  avoid  all  loss  is  not  previously  pul- 
verized, but  the  casserole  in  which  the  oxidation  took  place  is  filled 
with  water  and  heated  on  the  water-bath  for  several  hours.  The  hard 
mass  soon  softens,  and  by  repeated  treatment  in  this  manner  readily 
gives  up  all  its  arsenic  to  the  aqueous  solution ;  it  is,  however,  bet- 
ter to  have  the  carbonaceous  residue  in  contact  with  different  por- 
tions of  warm  water  for  about  24  hours  to  insure  the  complete 
extraction  of  the  arsenic. 

The  reddish-brown  fluid  containing  some  organic  matter  and 
arsenic  acid  is  now  evaporated  on  the  water-bath  to  dryness,  care 
being  taken  that  the  entire  residue  is  finally  obtained  in  one  cas- 


§  224.]  ARSENIC    IN   ORGANIC    MATTER.  785 

serole.  This  residue*  of  organic  matter  and  arsenic  is  warmed 
with  45  c.  c.  of  sulphuric  acid  No.  1,  and  the  clear  solution  so 
obtained,  or,  as  more  frequently  happens,  the  fluid  with  organic 
matter  in  suspension,  is  then  ready  for  introduction  into  the  MARSH 
apparatus. 

J.  Method  for  the  conversion  of  arsenic  acid  into  arsenetted 
hydrogen  and  then  into  metallic  arsenic. 

25-35  grms.  of  granulated  zinc  previously  alloyed  with  a  small 
quantity  of  platinum  are  placed  in  the  generator,  and  everything 
being  in  position,  the  MARSH  apparatus  is  filled  with  hydrogen  by  the 
use  of  a  small  quantity  of  acid  No.  1.  After  a  sufficient  time  has 
elapsed  the  gas  is  lighted  at  the  jet  and  the  glass  tube  heated  to  a 
bright  redness.  The  45  c.  c.  of  acid  No.  1  containing  the  arsenic 
is  then  poured  into  the  separating  funnel,  from  which  it  is  allowed 
to  flow  into  the  generator  at  such  a  rate  that  the  entire  fluid  is 
introduced  in  one  hour  or  one  hour  and  a  half ;  40  c.  c.  of  acid  No. 
2  are  then  poured  into  the  casserole,  to  which  considerable  organic 
matter  usually  adheres,  and  then  transferred  to  the  separating  fun- 
nel and  allowed  to  flow  slowly  into  the  generator,  and  lastly  45  c.  c. 
of  acid  No.  3.  In  this  manner  we  are  sure  to  have  all  of  Jfche 
arsenic  acid  dissolved  and  thus  carried  into  the  generator,  while  at 
the  same  time  the  stronger  acids  Nos.  2  and  3  ser\7e  as  a  rinse  fluid 
and  thereby  prevent  mechanical  loss,  while,  at  the  same  time,  the 
increasing  strength  of  acid  added  counteracts  the  diluting  effect  of 
the  reaction  so  that  the  strength  of  acid  remains  about  the  same 
during  the  entire  process  of  2^  to  3  hours  and  thereby  insures  a 
regular  flow  of  gas.  The  amount  of  time  required  will  vary  with 
the  amount  of  arsenic :  2 — 3  mgrms.  of  arsenic  will  require 
about  two  to  three  hours  for  the  entire  decomposition,  while  4 — 5 

*  When  the  residue  left  by  the  evaporation  of  the  water  is  quite  large,  it  is 
sometimes  better  to  reoxidize  it.  This  is  quickly  accomplished  by  adding  a  few 
cubic  centimetres  of  concentrated  nitric  acid  to  the  contents  of  the  casserole  and 
heating  on  the  air-bath  at  150° — 180°  C.  until  a  reddish  solution  is  obtained.  Then 
3 — 5  c.  c.  of  concentrated  sulphuric  acid  are  added  and  the  mixture  heated  at  the 
above  temperature  until  the  nitric  acid  is  completely  driven  off.  The  thin  black 
fluid  is  then  carefully  mixed  with  the  requisite  quantity  of  No.  1  acid,  and  intro- 
duced into  the  Marsh  apparatus.  Frequently  quite  a  heavy,  flocculent  precipitate 
separates  from  the  sulphuric  acid  solution.  This  does  not  interfere,  but  is  poured, 
together  with  the  fluid,  directly  into  the  receiving  bulb,  which  is  purposely  pro- 
vided with  a  delivery  tube  of  large  calibre. 


786  SPECIAL   PART.  [§  224. 

ingrmes.  will  need  perhaps  three  to  four  hours.  "Where  the 
amount  of  arsenic  is  small,  only  25  grms.  of  zinc  are  needed,  and 
but  45  c.  c.  of  acid  No.  1,  30  c.  c.  of  acid  No.  2,  and  30  c.  c.  of  acid 
No. -3  ;  but  when  4 — 5  mgrms.  of  arsenic  are  present  it  is  better 
to  take  the  first  mentioned  quantities  of  zinc  and  acids. 

The  arsenic  being  thus  collected  as  a  large  or  small  mirror  of 
metal,  the  tube  is  cut  at  a  safe  distance  from  the  mirror,  so  that  a 
tube  of  perhaps  2 — 6  grms.  weight  is  obtained.  This  is  carefully 
weighed  and  then  the  arsenic  removed  by  simple  heating ;  or,  if 
the  arsenic  is  to  be  saved  as  in  a  toxical  case,  dissolved  out  with 
strong  nitric  acid.  The  tube  is  then  cleaned,  dried,  and  again 
weighed,  the  difference  giving  the  weight  of  metallic  arsenic,  from 
which  by  a  simple  calculation  the  amount  of  arsenious  oxide  can 
be  obtained.  The  delicacy  of  the  method  is  shown  by  the  fact 
that  -00001  grm.  As2O3  when  introduced  into  100  grms.  of  beef 
yielded  by  this  method  a  distinct  mirror  of  metallic  arsenic.  In  a 
similar  manner  '000001  grm.  AsaO,  yielded  a  faint  mirror  of  arsenic, 
this  amount  appearing  to  be  the  limit. 

In  conducting  these  experiments  with  organic  matter,  after 
the  zinc  is  placed  in  the  generator,  15  drops  of  olive  oil 
are  allowed  to  flow  down  the  side,  and  this  as  the  fluid  is  intro- 
duced floats  on  top  and  thereby  prevents  any  troublesome  frothing. 
The  only  other  thing  to  be  guarded  against  is  the  too  rapid  intro- 
duction of  the  acids,  whereby  loss  as  well  as  frothing  of  the  mix- 
ture may  ensue,  and  secondly  the  heating  of  the  flask  by  the 
chemical  reaction.  If  necessary  this  latter  can  be  prevented  by 
placing  the  generator  in  a  glass  or  other  dish  so  that  a  stream  of 
cold  water  can  continually  play  about  it,  which  will  keep  the  flask 
sufficiently  cool  to  prevent  the  formation  of  any  hydrogen  sulphide 
which  might  sometimes  show  itself  in  slight  quantity. 

The  following  results  show  the  accuracy  of  the  method :  — 

Wt.  of  Metallic         Theoretical  Wt. 
Quantity  of  Arsenic  introduced.  Arsenic  found.       Metallic  Arsenic. 

100  grms.  beefsteak  with  .004  grm.  Asa08  '00300  '00303 


i 

< 


•004 
•004 
•003 
•005 
•005 


•00300  -00303 

•00290  -00303 

•00219  -00227 

•00369  -00378 

•00372  -00378] 


III. 


EXERCISES  FOR  PRACTICE. 


EXEEOISES  FOE  PRACTICE. 


THE  principal  point  kept  in  view  in  the  selection  of  these  exer- 
cises has  been  that  most  of  them,  and  more  particularly  the  first, 
should  permit  an  exact  control  of  the  results.  This  is  of  the 
utmost  importance  for  students,  since  a  well-grounded  self-reliance 
is  among  the  most  indispensable  requisites  for  a  successful  pursuit  of 
quantitative  investigations,  and  this  is  only  to  be  attained  by  ascer- 
taining for  one's  self  how  near  the  results  found  approach  the  truth. 

Xow  a  rigorously  accurate  control  is  practicable  only  in  the 
analysis  of  pure  salts  of  known  composition,  or  of  mixtures  com- 
posed of  definite  proportions  of  pure  bodies.  When  the  student 
has  acquired,  in  the  analysis  of  such  substances,  the  necessary  self- 
reliance,  he  may  proceed  to  the  analysis  of  minerals  or  products  of 
industry  in  which  such  rigorous  control  is  unattainable. 

The  second  point  kept  in  view  in  the  selection  of  these  exer- 
cises has  been  to  make  them  comprise  both  the  more  important 
analytical  methods  and  the  most  important  bodies,  so  as  to  afford 
the  student  the  opportunity  of  acquiring  a  thorough  knowledge  of 
every  branch  of  quantitative  analysis. 

Organic  analysis  offers  less  variety  than  the  analysis  of  inor- 
ganic substances ;  the  exercises  relating  to  the  former  branch  are 
therefore  less  numerous  than  those  relating  to  the  latter. 

I  would  advise  the  student  to  analyze  the  same  substance  re- 
peatedly, until  the  results  are  quite  satisfactory.  [It  is  a  good 
habit  always  to  carry  on  together  duplicate  analyses.  It  requires 
but  little  more  time  to  make  two  analyses  than  to  make  one,  and 
the  operator's  experience  is  thus  very  economically  doubled.] 

It  is  by  no  means  necessary  for  the  student  to  go  through  the 
whole  of  these  examples  ;  the  time  which  he  may  require  to  attain 
proficiency  in  analysis  depends,  of  course,  upon  his  own  abilities. 
One  may  be  a  good  analyst  without  having  tried  every  method  or 
determined  every  body.  A  few  substances  well  analyzed  yield 
more  profit  than  can  be  obtained  from  going  over  many  processes 
in  a  superficial  manner. 


790  EXEKCISES    FOK   PRACTICE. 

Finally,  the  student  is  warned  against  prematurely  attempting 
to  discover  new  methods ;  he  should  wait  until  he  has  attained  a 
good  degree  of  proficiency  in  general  chemistry,  and  more  particu- 
larly in  practical  analysis. 

EXEKCISES. 

A.  SIMPLE  DETERMINATIONS  IN  THE  GRAVIMETRIC  WAY,  IN- 
TENDED  TO  PERFECT  THE  STUDENT  IN  THE  PRACTICE  OP 
THE  MORE  COMMON  ANALYTICAL  OPERATIONS. 

[Ws  give  here,  in  the  first  place,  quite  full  details  of  all  the 
steps  in  the  estimation  of  chlorine  in  sodium  chloride,  including 
the  preparation  of  this  salt  in  a  state  of  purity.  This,  it  is  hoped, 
will  relieve  much  of  the  perplexity  which  the  beginner  must  at 
first  experience  in  making  out  a  scheme  of  operations  from  the 
various  separate  paragraphs  where  the  processes  are  described.  The 
student  should  not  fail,  however,  to  study  carefully  the  chapter  on 
operations  while  carrying  on  the  analysis,  nor  to  examine  every 
reference. 

1.  SODIUM  CHLORIDE. 

Preparation.  Sodium  chloride  is  far  less  soluble  in  hydro- 
chloric acid  than  in  water.  On  account  of  this  property  the  crude 
product — common  salt — may  be  purified  from  the  magnesium 
chloride  and  calcium  sulphate  which  it  contains  as  follows  : — To 
100  c.  c.  of  a  saturated  solution  add  very  gradually  an  equal  vol- 
ume of  pure  concentrated  hydrochloric  acid.  Drain  the  mass  of 
fine  crystals  which  separate  on  a  funnel,  the  throat  of  which  is 
loosely  closed  with  filter  paper.  Wash  with  a  small  volume  of 
pure  dilute  hydrochloric  acid,  and  at  last,  in  order  to  test  the  purity 
of  the  product,  allow  5  or  6  c.  c.  of  distilled  water  to  pass  through. 
Collect  the  water  that  runs  through  in  a  test  tube  separately,  and  add 
to  it  barium  chloride.  If  no  turbidity  results,  the  sodium  chloride 
is  free  from  sulphates  and  may  be  assumed  to  be  pure  enough  for 
analysis.  Kemove  it  from  the  funnel  and  dry  it  in  a  porcelain 
dish.  If  not  free  from  sulphates,  the  product  may  be  subjected  to 
a  repetition  of  the  process.  This,  however,  will  rarely  be  neces- 
sary.* 

*  When  large  quantities  of  pure  sodium  chloride  are  required,  it  is  more 
economical  to  prepare  it  from  a  solution  of  common  salt  by  saturating  the  solu- 
tion with  HC1  gas. 


EXERCISES    FOR   PRACTICE.  791 

A  portion*  of  the  salt  thus  obtained  is  heated  in  a  covered  cru- 
cible until  it  ceases  to  decrepitate,  but  not  to  fusion,  and  preserved 
in  a  weighing  tube  (like  a  small  test  tube,  but  not  flared  at  the 
mouth)  that  is  closed  with  a  soft,  well-fitting,  and  smooth  cork. 

ESTIMATION  OF  CHLORINE. 

1.  Weighing  out  the  substance.     The  tube  containing  the  pre- 
pared salt  is  wiped,  if  need  be,  from  dust.     The  cork  is  taken  out, 
and  by  means  of  a  bit  of  thin  paper,  or  a  clean  linen  handkerchief, 
any  particles  of  salt  adhering  to  the  cork,  and  to  the  inside  of  the 
tube  as  far  as  the  cork  reaches,  are  removed.     The  cork  is  replaced, 
and  the  whole  is  weighed  (see  §§  9  and  10),  the  weight  being  imme- 
diately recorded  in  the  note-book.     A  clean  beaker  or  assay-flask, 
of  about  200  c.  c.  capacity,  being  ready,  the  weighing-tube  is  held 
over  it  and  the  cork  carefully  removed.     A  portion  of  substance  is 
allowed  to  fall  in  the  vessel,  and,  the  cork  being  replaced,  the  tube 
is  again  counterpoised.     If  two  to  three  decigrammes  have  been 
emptied,  the  operator  is  ready  to  proceed.     If  less,  more  should  be 
transferred  from  the  tube  to  the  vessel.     If  more,  or  much  more, 
it  is  better  to  begin  anew,  by  weighing  off  another  portion  into 
another  beaker  or  flask.     In  this  manner  weigh  off  two  portions  in 
separate  vessels,  so  as  to  carry  together  duplicate  analyses.     Xow 
affix  a  piece  of  gummed  paper  to  each  vessel,  and  label  them  to 
correspond  with  their  designation  in  the  note-book. 

2.  Solution  and  precipitation.     Dissolve  the  weighed  portions, 
each  in  about  100  c.  c.  of  cold  distilled  water,  add  a  few  drops  of 
pure  nitric  acid,  and,  lastly,  clear  solution  of  silver  nitratef  until 
further  addition  no  longer  produces  a  precipitate. 

Agitate  the  mixture  well,  but  with  care  to  avoid  loss.  This  can 
be  done  by  shaking,  if  a  flask  be  in  use,  or  by  stirring  with  a  glass 
rod,  if  a  beaker  be  employed. 

Set  the  vessel  aside  in  a  dark  place,  covered  with  paper  or  a 
watch-glass  to  exclude  dust,  and  let  stand  for  about  12  hours,  or 
until  the  precipitate  has  subsided  and  the  liquid  above  it  is  perfect!  y 
clear,  then  add  a  drop  of  silver  nitrate  to  make  sure  that  the  pre- 
cipitation is  complete  (if  not  complete,  add  more  solution  of  silver, 
and  let  stand  again  for  some  hours). 

*  Pure  sodium  chloride  is  needed  in  other  analyses,  and  the  chief  part  of  what 
Is  thus  prepared  should  he  carefully  bottled  and  reserved  for  future  use. 

f  Solution  of  a  silver  coin  in  nitric  acid  answers  for  this  purpose  as  well  as 
pure  nitrate,  provided  it  be  clear  and  contain  but  little  free  acid. 


792  EXERCISES   FOR   PRACTICE. 

3.  Filtration.     A  filter  is  placed  in  a  funnel  at  least  J  inch 
deeper  than  itself,  and  moistened  with  water,  at  the  same  time 
being  carefully  pressed  down  so  that  its  edges  touch  the  glass  at  all 
points.     The  funnel  being  supported  on  a  stand,  a-  clean  beaker  or 
flask  is  put  beneath  it,  and  the  operator  proceeds  to  pour  the  liquid 
— on  whose  surface  some  particles  of  silver  chloride  usually  float — 
into  the  filter,  leaving  the  bulk  of  the  precipitate  undisturbed.    To 
do  this  without  loss  the  following  precautions  may  be  regarded :  a. 
Touch  the  edge  or  lip  of  the  vessel  with  a  very  slight  coat  of  tallow  (a 
small  bit  of  which  is  kept  at  hand  under  the  edge  of  the  work- 
table,  and  is  applied  with  the  finger),     b.  Pour  slowly  over  the 
greased  place,  along  a  glass  rod  held  nearly  vertical,  so  directing 
the  stream  that  it  shall  strike  against  the  side,  not  into  the  vertex 
of  the  filter,     c.  When  the  filter  is  filled  to  within  J  inch  of  the 
top  discontinue  the  pouring,  bringing  the  rod  into  the  vessel  con- 
taining the  precipitate,  after  it  has  drained  so  that  nothing  will  fall 
from  it. 

The  pouring-rod  may  be  simply  straight,  and  an  inch  longer  than  the  diago- 
nal of  the  vessel,  or  when  it  is  desirable  not  to  disturb  a  precipitate,  it  may  be 
3 — 4  inches  long  and  bent  siphon  fashion  so  as  to  hang  on  the  edge  of  a  beaker 
or  flask.  In  either  case  its  end  should  be  rounded  by  fusion,  and  those  portions 
along  which  the  liquid  flows  must  not  be  handled. 

The  vessel  containing  the  precipitate,  as  well  as  that  which 
receives  the  filtrate,  and  likewise  the  funnel,  should  be  kept  covered 
as  much  as  possible  in  all  cases  when  nicety  is  required,  to  prevent 
access  of  dust,  insects,  &c. 

The  most  convenient  covers  are  large  watch-glasses,  but  square  plates  of 
glass,  or  even  cards,  will  generally  answer. 

The  filtration  of  silver  chloride  should  be  conducted  without 
exposing  it  to  strong  light,  whereby  it  is  blackened,  with  loss  of 
chlorine,  p.  168. 

4.  When  all,  or  nearly  all,  the  liquid  has  passed  the  filter,  it 
remains  to  wash  and  to  transfer  the  precipitate. 

These  operations  may  be  carried  on  as  follows :  pour  about  100 
c.c.  of  cold  distilled  water  upon  the  precipitate,  which  mostly 
remains  in  the  vessel  where  it  was  formed,  and  agitate  vigorously, 
in  order  to  break  up  and  divide  the  lumpy  silver  chloride,  and  bring 
every  part  of  it  perfectly  in  contact  with  the  water. 


EXERCISES   FOR   PRACTICE.  793 

When  in  a  beaker,  the  agitation  must  be  made  with  great  caution,  by  means 
of  a  glass  stirring-rod ;  when  in  a  narrow-mouthed  flanged  flask,  this  may  be 
tightly  closed  by  a  perfectly  smooth  cork  (softened  for  the  purpose  by  squeezing) 
and  then  shaken  violently. 

The  water  and  precipitate  are  now  poured  together  upon  the 
niter,  with  the  precautions  before  detailed.  The  last  portions  of  the 
precipitate  are  removed  from  the  beaker  or  flask  by  repeated  rins- 
ings, in  which  a  wash-bottle  like  flg.  36,  p.  81,  may  be  conveniently 
employed. 

Any  portions  of  precipitate  that  adhere  to  the  sides  of  the  ves- 
sel too  strongly  to  be  removed  by  a  stream  from  the  wash-bottle 
must  be  nibbed  off.  For  this  purpose  the  feather  is  employed. 

It  is  made  from  a  goose-quill,  by  cutting  off  the  extreme  tip  for  an  inch  or 
so,  and  smoothly  trimming  away  the  beard,  except  a  portion  of  one  half-inch  in 
length  on  the  inside  of  the  curve.  The  tubular  part  may  be  removed  or  not, 
to  suit  the  depth  of  the  dish  which  is  to  be  washed. 

The  dish  being  wiped  clean,  externally,  a  little  water  is  put  in  it, 
and,  it  being  held  up  to  the  light,  its  whole  interior  surface  is  gently 
nibbed  with  the  feather,  then  rinsed,  rubbed  again  and  rinsed,  so 
long  as  careful  inspection  discovers  any  portions  of  adhering  pre- 
cipitate ;  finally,  the  feather  is  rinsed  in  a  stream  of  water,  the 
rinsings  in  each  case  being  poured  upon  the  filter. 

The  washing  is  now  continued  by  help  of  the  wash-bottle.  A 
jet  of  cold  water  is  directed,  first,  upon  the  interior  of  the  funnel, 
just  above  the  filter,  then  upon  the  edge  of  the  filter  itself.  If 
thrown  immediately  against  the  paper,  this  is  liable  to  be  perfo- 
rated. The  stream  of  water  is  carried  around  the  edge  of  the  filter 
until  the  latter  is  nearly  full,  and  the  liquid  is  then  allowed  to  drain 
off.  This  process  is  repeated  until  a  portion  of  the  wash-water, 
collected  to  the  depth  of  an  inch  in  a  test  tube  containing  a  drop 
of  hydrochloric  acid,  gives  no  turbidity  of  silver  chloride.  When 
this  is  accomplished,  the  precipitate  is  washed  down  into  the  ver- 
tex of  the  filter.  The  funnel  is  then  closely  covered  with  paper 
(p.  85),  labelled,  allowed  to  drain  thoroughly,  and  set  away  in  a 
warm  place  for  drying. 

5.  Drying  the  filter.  In  public  laboratories  a  heated  closet  is 
usually  provided  for  drying  filters.  Its  temperature  should  not 
exceed  100°  C.  In  default  of  such  special  arrangement,  the  dry- 
ing may  be  effected  over  the  register  of  a  hot-air  furnace,  or  over  a 
common  stove  or  kitchen  range. 


794  EXERCISES   FOR   PRACTICE. 

The  funnel  may  also  be  supported  on  a  retort-stand  over  a  sheet 
of  iron,  which  is  heated  beneath  by  a  lamp,  or  may  be  placed  at 
once  in  the  water-bath.  See  §  50. 

6.  When  the  precipitate  is  perfectly  dry  we  proceed  to  ignite 
it  for  weighing. 

A  small  porcelain  crucible  (platinum  must  not  be  used)  is 
cleaned,  gently  ignited,  and  when  cool  (after  15 — 20  minutes) 
weighed. 

The  work-table  being  clean,  two  small  sheets  of  fine  and  smooth 
writing  or  glazed  paper  are  opened  and  laid  down  side  by  side. 
The  filter  is  removed  from  the  funnel  and  carefully  inverted  upon 
one  of  the  papers.  The  precipitate  is  loosened  from  the  filter  by 
squeezing  and  rubbing  gently  between  the  fingers,  and  when  it  has 
mostly  separated  the  filter  is  lifted,  reversed,  and  any  portions  of 
silver  chloride  still  adhering  are  loosened  by  rubbing  its  sides 
together.  What  is  thus  detached  is  poured  or  shaken  out  on  the 
paper. 

The  filter  is  now  spread  out  as  a  half -circle  upon  the  other  sheet 
of  paper,  and,  beginning  with  the  straight  edge,  is  folded  up  into 
a  narrow  flattened  roll,  the  two  ends  of  which  are  then  brought 
together.  In  this  way  those  central  portions  of  the  filter  to 
which  particles  of  precipitate  adhere  are  thoroughly  enveloped  by 
the  exterior  parts,  so  that  in  the  subsequent  burning  nothing  can 
-easily  escape. 

The  crucible  being  placed  on  the  glazed  paper,  the  filter  is 
taken  by  the  two  free  ends  in  a  clean  pincers  or  tongs,  put  to  the 
flame  of  a  lamp  to  set  it  on  fire,  and  then  held  over  the  crucible 
until  it  is  completely  charred.  It  is  then  dropped  into  the  crucible 
and  moistened  with  two  or  three  drops  of  nitric  acid.  The  cruci- 
ble is  covered  and  placed  over  a  low  flame  until  its  contents  are  dry  ; 
it  is  then  heated  somewhat  stronger,  whereby  the  carbon  is  nearly 
or  entirely  consumed. 

The  crucible  being  allowed  to  cool,  one  more  drop  of  nitric 
acid,  and  afterwards  a  drop  of  hydrochloric  acid,  is  added  to  the 
residue,  and  it  is  heated  cautiously,  without  the  cover,  until  fumes 
cease  to  escape.  This  treatment  with  nitric  acid  serves  to  destroy 
carbon  and  convert  any  reduced  silver  to  nitrate,  which  the  hydro- 
'  -chloric  acid  in  turn  transforms  into  chloride.  When  the  crucible 
is  cool,  it  is  placed  again  on  the  paper,  and  the  precipitate  is  poured 
into  it  from  the  other  sheet,  the  last  particles  being  detached  by 


EXERCISES   FOR   PRACTICE.  795 

cautious  tapping  with  the  fingers  underneath,  or  by  the  use  of  a 
clean  camePs-hair  pencil. 

The  crucible  is  now  put  over  a  low  flame  and  heated  cautiously 
until  the  silver  chloride  begins  to  fuse  on  the  edges.  It  is  then 
covered  and  let  cool.  When  cold  it  is  weighed.  Read  §  115,  1, 
and  the  references  there  made. 

7.  ^Record  and  calculation  of  results.  The  amount  of  silver 
chloride  is  learned  by  subtracting  from  the  total  the  joint  weight 
of  the  crucible  and  filter-ash.  The  quantity  of  chlorine  is  obtained 
by  multiplying  the  amount  of  silver  chloride  by  the  decimal  0*2473. 
In  order  to  compare  results  they  are  reduced  to  per  cent,  statements 
by  the  following  proportion  : 

Substance  :  chlorine  in  substance  :  :  100  :  chlorine  in  100 ;  i.e. 
per  cent. 

The  record  may  be  made  as  follows :  It  is  well  to  work  out  the  calculations 
in  full  in  the  weight-book,  as  in  case  of  mistake  the  data  are  at  hand  for  revision. 

No.  1.  No.  2. 

NaCl  and  tube 6'615  6'180 

"    —substance 6'180  5'765 


Substance -435 

Crucible,  AgCl  and  Ash 15  '3630 

Cr 14-298    )  u.2<m  13'309 

Ash -0015  f  M  -0015 


AgCl 1-0635  1-0165 

0-2473  0-2473 


31905  30495 

74445  71155 

42540  40660 

21270  20330 


Cl. =  '26300355  -25138045 

•435)  26-300355  (60'46  '415)  25-138045  (60'57 

2610  2490 

2003  2380 

1740  2075 

2635  3054 

2610  2905 

Found.  Calculated. 

No.  1.  No.  2. 

Chlorine 60'46  60'57  60-62 

We  have  here  employed  the  simplest  arithmetical  calculation.  It  is  well  to 
duplicate  the  calculation  with  help  of  the  tables  given  in  the  Appendix. 

The  first  determination  given  above  is  not  only  fair  for  this  method,  but 
answers  all  ordinary  purposes.  The  second  is  very  good,  though  with  care  still 
closer  accordance  with  theory  can  be  easily  attained.] 


796  EXERCISES    FOR  PRACTICE. 

2.  IRON. 

Procure  10 — 15  grms.  of  fine  bright  pianoforte  wire,  cut  it  into 
lengths  of  about  O3  gran,  and  keep  it  free  from  rust  in  a  dry  bottle. 

Weigh,  on  a  watch-glass,  for  each  estimation,  about  0*3  grm. 
of  wire,  and  dissolve  in  hydrochloric  acid,  with  addition  of  nitric 
acid.  The  acids  are  diluted  with  a  little  water. 

The  solution  is  effected  by  heating  in  a  moderate-sized  beaker 
covered  with  a  watch-glass.  When  complete  solution  has  ensued, 
and  the  color  of  the  fluid  shows  that  all  the  iron  is  dissolved  as 
ferric  chloride  (if  this  is  not  the  case  some  more  nitric  acid  must 
be  added),  rinse  the  watch-glass,  dilute  the  fluid  to  about  150  c.c., 
heat  to  incipient  ebullition,  add  ammonia  in  moderate  excess, 
filter  through  a  filter  exhausted  with  hydrochloric  acid,  &c. 
(Comp.  §  113,  1,  a.}  If  BTJNSEN'S  filtering  apparatus  is  employed, 
proceed  as  described  on  p.  97. 

As  the  ferric  oxide  generally  contains  a  small  quantity  of  silica 
partially  arising  from  the  silicon  in  the  wire,  partially  taken  up 
from  the  glass  vessels),  after  it  is  weighed,  digest  with  fuming 
hydrochloric  acid  for  some  hours;  when  the  ferric  oxide  is  all 
dissolved,  dilute,  collect  the  silica  on  a  small  filter,  ignite  and 
weigh.  The  weight  is  the  silica  -f-  the  ashes  of  both  filters. 

The  records  are  made  as  follows : — 

Watch-glass  -|-  iron 10*3192 

"  empty 9*9750 


Iron -3442 

Crucible  -f-  ferric  oxide  +  silica  +  filter  ash.  17'0703 
empty . ....   16*5761 

•4942 
Ash  of  large  filter -0008 

Ferric  oxide  +  silica -4934 

Crucible  +  silica  +  ashes  of  both  filters 16*5809 

empty 16*5T61 

•0048 
Ashes  of  the  filters -0014 

Silica -0034 

•4934  —  -0034  =  -4900  ferric  oxide  =  -343  iron 
which  gives  99'65  per  cent. 


EXERCISES    FOR   PRACTICE.  797 


3.  LEAD  ACETATE. 

Determination  of  Lead. — Triturate  the  dry  and  non-effloresced 
crystals*  in  a  porcelain  mortar,  and  press  the  powder  between 
sheets  of  blotting  paper  until  fresh  sheets  are  no  longer  moistened 
by  it. 

a.  Weigh  about  1  grm.,  dissolve  in  water,  with  addition  of  a 
few  drops  of  acetic  acid,  and  proceed  exactly  as  directed  §  116, 1,  a. 

b.  Weigh  about  1  grm.,  and  proceed  exactly  as  directed  §  116, 4. 

PbO 223-00  58-84 

(C,H3O)aO     .    .     .      102-00  26-91 

3H,O 54-00  14-25 

379-00  100-00 


4.  POTASH  ALUM. 

Determination  of  Aluminium. — Press  pure  triturated  potash 
alum  between  sheets  of  blotting  paper ;  weigh  off  about  2  grm., 
dissolve  in  water,  and  determine  aluminium  as  directed  p.  241,  a. 

K2O 94-26  9-93 

A12O3   ....  103-00  10-85 

4SO, 320-00  33-71 

24H,O      ....  432-00  45-51 


949-26  100-00 


5.  POTASSIUM  DICHROMATE. 

Determination  of  Chromic  Acid. — Fuse  pure  potassium  dichro- 
mate  at  a  gentle  heat,  weigh  off  -4 — -6  grm.,  dissolve  in  water, 
reduce  with  hydrochloric  acid  and  alcohol,  and  proceed  as  directed 
§130,1.,  a,  a. 

K2O     .  94-26  31-93 

2CrO3       ....     200-96  68-07 

295-22  100-00 

*  Obtained  by  dissolving  the  pulverized  commercial  salt  in  hot  water  nearly 
to  saturation,  filtering,  adding  a  drop  or  two  of  acetic  acid  to  the  solution,  and 
slowly  evaporating  to  crystallization. 


798  EXERCISES    FOR   PRACTICE. 

6.  ARSENIOUS  OXIDE. 

Dissolve  about  0'2  grm.  pure  arsenious  oxide  in  small  lumps  in 
a  middle-sized  flask,  with  a  glass  stopper,  in  some  solution  of  soda, 
by  digesting  on  the  water-bath ;  dilute  with  a  little  water,  add 
hydrochloric  acid  in  excess,  and  then  nearly  fill  the  flask  with  clear 
hydrogen  sulphide  water.  Insert  the  stopper  and  shake.  If  the 
hydrogen  sulphide  is  present  in  excess,  the  precipitation  is  termi- 
nated ;  if  not,  conduct  an  excess  of  hydrogen  sulphide  gas  into  the 
fluid ;  proceed  in  all  other  respects  exactly  as  directed  §  127,  4. 

As, 150  75-76 

(X  48  24-24 


198  100-00 


B.  COMPLETE  ANALYSIS  OF  SALTS  IN  THE  GRAVIMETRIC  WAY; 
CALCULATION  OF  THE  FORMULAE  FROM  THE  RESULTS  OB- 
TAINED (see  "  Calculation  of  Analyses,"  in  the  Appendix). 

7.  CALCIUM  CARBONATE.* 

Heat  pure  calcium  carbonate  in  powder  (no  matter  whether 
Iceland  spar  or  the  artificially  prepared  substance,  see  "  QuaL 
Anal.,"  Am.  Ed.,  p.  87)  gently  in  a  platinum  crucible. 

a.  Determination  of  Calcium. — Dissolve  in  a  covered  beaker 
about  1  grm.  in  dilute  hydrochloric  acid,  heat  gently  until  the 
carbonic  acid  is  completely  expelled,  and  determine   calcium   as 
directed  §  103,  2,  £,  a. 

b.  Determination  of  Carbonic  Acid. — Determine  in  about  0*8 
grm.  the  carbonic  acid  after  §  139,  II.,  e. 

CaO 56  56-00 

CO, 44  44-00 

100  100-00 

8.  CTJPEIG  SuLPHATE.f 

Triturate  the  pure  crystals  J  in  a  porcelain  mortar,  and  dry  as 
directed  p.  47,  a. 

*  Ca  <  £J  >  CO.  f  Cu  <  £J  >  SOQ  +  5H2O. 

t  [Boil  a  solution  of  commercial  blue  vitriol  with  a  little  pure  binoxide  of 
lead  to  oxidize  the  iron,  then  with  a  little  barium  carbonate  to  precipitate  it, 
filter  and  crystallize.— H.  WURTZ,  Am.  Jour.  (2),  XXVI.  367.] 


EXERCISES   FOR    PRACTICE.  799 

a.  Determination  of  Water  of  Crystallization. — 1.  Weigh  off 
in  a  crucible  1 — 2  grm.  of  the  salt,  and,  having  first  heated  the  air- 
bath  (fig.  22,  p.  52)  so  that  the  thermometer  stands  steadily  at 
120° — 140°,  introduce  the  crucible,  uncovered,  and  maintain  the 
heat  for  two  hours.  Then  cool  the  crucible  in  a  desiccator  and 
weigh.  Heat  again  as  before,  for  an  hour,  and  weigh.  If  need  be, 
repeat  the  heating  until  no  more  loss  occurs.  The  loss  expresses 
the  amount  of  water  expelled  at  the  temperature  of  140°,  or  four 
molecules.  2.  Raise  the  temperature  of  the  air-bath  to  between 
250° — 260°  and  proceed  as  before.  The  loss  is  the  one  molecule 
of  strongly  combined  water  of  crystallization,  or,  as  some  term  it, 
water  of  halhydration. 

o.  Determination  of  Sulphuric  Acid. — In  another  portion  of 
the  copper  sulphate  (about  1*5  grm.)  determine  the  sulphuric  acid 
according  to  §  132,  I.,  1. 

d.  Determination  of  Copper. — In  about  1-5  grm.  determine 
the  copper  as  cuprous  sulphide,  as  directed  §  119,  3,  a. 

CuO 79-40  31-83 

SO, 80-00  32-08 

H2O 18-00  7-22 

4aHO 72-00  28.87 


249-40  100-00 

9.  CRYSTALLIZED  HYDROGEN  SODIUM  PHOSPHATE.* 

a.  Determination  of  the  Water  of  Crystallization.  —  Heat 
about  1  grm.  of  the  pure  uneffloresced  salt  in  a  platinum  crucible, 
slowly  and  moderately,  first  in  the  water-bath,  then  in  the  air-bath, 
and  finally  some  distance  above  the  lamp  (not  to  visible  redness) ; 
the  loss  of  weight  gives  the  amount  of  water  of  crystallization. 

I.  Determination  of  the  Hydrogen  in  the  Anhydrous  Salt. — 
Ignite  the  residue  of  a.  The  loss  is  water. 

c.  Determination  of  Phosphoric  Acid. 

a.  Treat  1-5 — 2  grm.  of  the  salt  as  directed  §  134,  J,  a. 
ft.  Treat  about  0'2  grm.  of  the  salt  as  directed  §  134,  £,  ft. 

I  recommend  the  student  to  perform  the  determination  by  each 
of  these  methods,  as  they  are  both  in  common  use  in  the  analytical 
laboratory. 

*  HO    \ 

NaO  -   -  PO  -f  24H2O. 
XaO  ^ 


800  EXERCISES    FOR   PRACTICE. 

d.  Determination  of  Sodium. — Treat  about  1*5  grm.  of  the 
salt,  according  to  §  135,  «,  a.  After  the  excess  of  lead  has  been 
separated  with  hydrogen  sulphide,  the  fluid  is  to  be  evaporated  to 
dryness  and  weighed  in  a  platinum  dish ;  comp.  §  69,  &,  and 

§  98,  2. 

P,0 142-00  19-83 

2NaaO 124-16  IT'34 

HaO        18-00  2-51 

24H,O    .....  432-00  60-32 


716-16         •   100-00 

10.  SILVER  CHLORIDE. 

Ignite  pure  fused  silver  chloride  in  a  stream  of  pure  dry  hydro- 
gen till  complete  decomposition  is  effected,  and  weigh  the  silver 
obtained.  The  ignition  may  be  performed  in  a  light  bulb  tube,  or 
in  a  porcelain  boat  in  a  glass  tube,  or  in  a  porcelain  crucible  with 
perforated  cover  (§  115,  4). 

The  chlorine  may  be  in  this  case  estimated  by  difference ;  if 
you  want  to  determine  it  directly,  proceed  as  directed  §  141,  II.,  £. 

Ag 107-93  75-27' 

01  35-46  24-73 


143-39  100-00 

11.  MERCURIC  SULPHIDE. 
Reduce  to  a  fine  powder,  and  dry  at  100°. 

a.  Determination    of   Sulphur. — Treat   about   0*5   grm.,    as 
directed  §  148,  /?,  p.  466,  using  nitric  acid  and  potassium  chlorate. 
Precipitate  with  barium  chloride,  and  after  decanting  the  clear 
liquid  into  a  filter,  boil  the  barium    sulphate  twice  with    dilute 
solution  of  ammonium  acetate  and  finally  wash  with  hot  water. 

b.  Determination  of  Mercury. — Dissolve  about  0*5   grm.  as 
before,  dilute,  and  allow  to  stand  in  a  moderately  warm  place 
until  the  smell  of  chlorine  has  nearly  gone  off ;  filter  if  necessary, 
add  ammonia  in  excess,  heat  gently  for  some  time,  add  hydro- 
chloric acid  until  the  white  precipitate  of  mercuric  chloride  and 
amide  of  mercury  is  redissolved,  and  treat  the  solution,  which  now 
no  longer  smells  of  chlorine,  as  directed  §  118,  3. 

Hg 200-00  86-21 

S      .     .  32-00  13-79 


232-00  100-00 


EXERCISES  FOR  PRACTICE.  801 


12.  CRYSTALLIZED  CALCIUM  SULPHATE.* 

Select  clean  and  pure  cystals  of  selenite,  triturate  to  a  coarse 
powder,  avoiding  as  much  as  possible  exposure  to  the  air,  and  cork 
up  in  a  weighing  tube. 

a.  Determination  of  Water. — After  §  35,  a,  a. 

o.  Determination  of  Sulphuric  Add  and  Calcium  (§  132, 
II,  &,  a). 

CaO 56  32-56 

SO,    .    '. 80  46-51 

2HaO 36  20-93 

172  100-00 


C.  SEPARATION  OF  TWO  BASIC  OR  TWO  ACID  RADICALS  FROM 
EACH  OTHER,  AND  DETERMINATIONS  IN  THE  VOLUMETRIC 
WAY. 

13.  SEPARATION  OF  IRON  FROM  MANGANESE. 

Dissolve  in  hydrochloric  acid  about  0'2  grm.  fine  pianoforte 
wire,  and  about  the  same  quantity  of  ignited  protosesquioxide  of 
manganese  (prepared  as  directed  §  109,  1,  a) ;  heat  with  a  little 
nitric  acid,  and  separate  the  two  metals  by  means  of  sodium  acetate 
(p.  517).  Determine  the  manganese  as  directed  §  109,  3. 


14.  VOLUMETRIC  DETERMINATION  OF  IRON  BY  SOLUTION  OF 
POTASSIUM  PERMANGANATE. 

a.  Graduation  of  the  Solution  of  Potassium  Perman- 
ganate. 

a.  By  metallic  iron  (fine  piano  wire)  dissolved  in  dilute  sul- 
phuric acid  (p.  268). 

ft.  By  ammonium  oxalate  (p.  270). 

o.  Determination  of  Iron  in  Ammonium  Ferrous  Sul- 
phate. 

In  solution  acidified  with  sulphuric  acid  (p.  272,  ft). 
The  formula  requires  18-37  per  cent,  of  FeO. 


*Ca 


802  EXERCISES    FOR    PRACTICE. 

c.  .Determination  of  the  Iron  in  a  Limonite. 
Powder  finely,  dry  at  100°,  weigh  off  2  grm.,  heat  with  strong 
hydrochloric  acid  till  the  ferric  oxide  is  completely  dissolved,  dilute 
the  acid  solution  with  twice  its  volume  of  water,  filter,  evaporate 
with  sulphuric  acid,  dilute  the  ferric  sulphate  to  500  c.c.,  and  in 
two  or  three  portions  of  100  c.c.  each  reduce  ferric  to  ferrous 
sulphate,  and  determine  iron  as  directed  in  §  113,  &,  p.  278. 

i 

15.  VOLUMETRIC  DETERMINATION  OF  IRON  WITH   SODIUM 
THIOSULPHATE. 

a.  Graduation  of  the  Solution  of  Sodium  Thiosulphate. 

a.  By  solution  of  ferric  chloride  (p.  280). 
ft.  By  ammonia-iron-alum  (p.  119).      2  grms.  to  be  weighed 
off,  dissolved  in  water  with  addition  of  hydrochloric  acid. 

h.  Determination  of  Iron  in  Limonite. 

Decompose  2  to  3  grms.  with  concentrated  hydrochloric  acid. 
Transfer  to  a  500  c.c.  flask,  mix  well  the  solution  diluted  to 
500  c.c.,  and  determine  repeatedly  iron  in  portions  of  100  c.c. 
each,  after  §  113,  3,  b.  (If  the  ore  contains  ferrous  iron,  oxidize  the 
hydrochloric  acid  solution  with  potassium  chlorate,  avoiding  need- 
less excess,  and  concentrate  it  one  half  to  remove  excess  of  chlorine. 
See  §  112,  1,  p.  266.) 

16.  DETERMINATION  OF  NITRIC  ACID  IN  POTASSIUM  NITRATE. 

Heat  pure  nitre,  not  to  fusion,  and  transfer  it  to  a  tube  provided 
with  a  cork. 

Treat  0*5  grm.  as  directed  p.  4Y3,  ft. 

K2O 94-26  46-59 

N,O§ 108-08  53-41 

202-34  .  100-00 

IT.  SEPARATION  OF  MAGNESIUM  FROM  SODIUM. 

Dissolve  about  0-4  grm.  pure  recently  ignited  magnesia  and 
about  0-5  grm.  pure  well-dried  sodium  chloride  in  dilute  hydro- 
chloric acid  (avoiding  a  large  excess),  and  separate  by  one  of  the 
methods  described  in  §  153,  4. 


EXERCISES   FOR   PRACTICE.  803 


18.  SEPARATION  or  POTASSIUM  FROM  SODIUM. 

Triturate  crystallized  sodium  potassium  tartrate  (Rochelle  salt), 
press  between  blotting  paper,  weigh  off  about  1*5  grm.,  heat  in  a 
platinum  crucible,  gently  at  first,  then  for  some  time  to  gentle 
ignition.  The  carbonaceous  residue  is  first  extracted  with  water, 
finally  with  dilute  hydrochloric  acid,  the  acid  fluid  is  evaporated  in 
a  weighed  platinum  dish,  and  the  chlorides  are  weighed  together 
(§  97,  2).  Then  separate  them  by  platinic  chloride  (p.  481, 1),  and 
calculate  from  the  results  the  quantities  of  soda  and  potassa  sever- 
ally contained  in  the  Rochelle  salt. 

K3O 94-26  16-70 

Na2O 62-08  11-00 

C8H8O10  ....  264-00  46-78 

8ILO  144-00  25-52 


564-34      100-00 

19.  VOLUMETRIC  DETERMINATION  OF  CHLORINE  IN  CHLORIDES. 

a.  Preparation  and  examination  of  the  solution  of  silver  nitrate 
(§  141,  L,  J,  «). 

~b.  Indirect  determination  of  the  sodium  and  potassium  in 
Rochelle  salt,  by  volumetric  estimation  of  the  chlorine  in  the 
alkali  chlorides  prepared  as  in  No.  18.  For  calculation,  see  "  Cal- 
culation of  Analyses,"  in  the  Appendix. 

20.  ACIDIMETRY. 

a.  Preparation  of  standard  acid  and  alkali  solutions.  Sulphuric 
acid  and  potash,  or  hydrochloric  acid  and  ammonia  may  be  used 
(§  192). 

5.  Determination  of  acid  in  hydrochloric  acid,  by  the  specific 
gravity  (p.  677). 

c.  Determination  of  acid  in  the  same  hydrochloric  acid,  by  an 
alkaline  fluid  of  known  strength  (p.  684). 

d.  Determination  of  acid  in  colored  vinegar,  by  saturation  with 
a  standard  alkaline  solution.     (Application  of  test-papers,  p.  684). 

21.  ALKALIMETRY. 

a.  Preparation  of  the  normal  acid  after  DESCROIZILLES  and 
GAY-LUSSAC  (§  195). 


804  EXERCISES    FOR    PRACTICE. 

I.  Valuation  of  a  soda-ash  after  expulsion  of  the  water  by  gentle 
ignition. 

a.  After  DESCROIZILLES  and  GAY-LUSSAC  (§  195). 
/3.  After  MOHR  (§  196). 

22.  DETERMINATION  OF  .  AMMONIUM. 

Treat  about  O8  grm.  chloride  of  ammonium  as  directed  §  99, 
3,  a. 


4    .  .  18-04  .  .  33-72   •      NH3    .  .  .  17'04  .  .  31-85 
Cl          .  35-46  .  .  66-28          HC1    .  .  .  36*46  .  .  68-15 


53-50       100-00  53-50       100-00 

I).  ANALYSIS   OF  ALLOYS,   MINERALS,  INDUSTRIAL   PRODUCTS, 
&c.,  IN  THE  GRAVIMETRIC  AND  VOLUMETRIC  WAY. 

23.  ANALYSIS  OF  BRASS. 

Brass  consists  of  from  25  to  35  per  cent,  of  zinc  and  from  75  to 
65  per  cent,  of  copper.  It  also  contains  usually  small  quantities  of 
tin  and  lead,  and  occasionally  traces  of  iron. 

Dissolve  about  2  grm.  in  nitric  acid,  evaporate  on  the  water- 
bath  to  dryness,  moisten  the  residue  with  nitric  acid,  add  some 
water,  warm,  dilute  still  further,  and  filter  off  any  residual  meta- 
stannic  acid  (§  126,  1,  a).  Add  to  the  filtrate,  or,  if  the  quantity 
of  tin  is  very  inconsiderable,  directly  to  the  solution,  about  20  c.c. 
dilute  sulphuric  acid  ;  evaporate  to  dryness  on  the  water-bath,  add 
50  c.c.  water,  and  apply  heat.  If  a  residue  remains  (lead  sul- 
phate), filter  it  off,  and  treat  it  as  directed  §  116,  3.  In  the  filtrate, 
separate  the  copper  from  the  zinc  by  sodium  thiosulphate  (p.  540). 
If  the  quantity  of  iron  present  can  be  determined,  determine  it  in 
the  weighed  oxide  of  zinc  (§  160).  ^ 

24.  ANALYSIS  OF  SOLDER  (TiN  AND  LEAD). 

Introduce  about  1-5  grm.  of  the  alloy,  cut  into  small  pieces, 
into  a  flask,  treat  it  with  nitric  acid,  and  proceed  as  directed  p.  339, 
to  effect  the  separation  and  estimation  of  the  tin. 

Mix  the  filtrate  in  a  porcelain  dish  with  pure  dilute  sulphuric 
acicf,  evaporate  the  nitric  acid  on  the  water-bath,  and  proceed  with 
the  lead  sulphate  obtained  as  directed  §  116,  3.  Test  the  fluid 


EXERCISES    FOR   PRACTICE.  805 

filtered  from  the  lead  sulphate  with  hydrogen  sulphide  and  ammo- 
nium sulphide  for  the  other  metals  which  the  alloy  might  contain 
besides  tin  and  lead.  The  stannic  oxide  may  contain  small  quan- 
tities of  iron  or  copper ;  it  is  tested  for  these  by  fusion  with 
sodium  carbonate  and  sulphur  (p.  558). 
• 

25.  ANALYSIS  OF  A  DOLOMITE. 
See  §  210. 

26.  ANALYSIS  OF  FELSPAR. 

a.  Decomposition  by  sodium  carbonate  (§  140,  II.,  b) ;  removal 
of  the  silicic  acid ;  precipitation  of  the  aluminium  with  the  small 
quantity  of  iron  as  hydroxides  by  ammonia  (in  platinum  or  Berlin 
porcelain,  not  in  glass   vessels)  after  §  156,  1,  (37) ;  separation  of 
barium,  if  present,  from  the  filtrate  with  dilute  sulphuric  acid,  and 
then  of  calcium  with  ammonium  oxalate,  §  154  (28).    Finally,  solu- 
tion of  the  weighed    alumina  in   concentrated  hydrochloric  acid, 
separation  and  weighing  of  traces  of  silica  if  present ;  evaporation 
with  sulphuric  acid  and  volumetric  determination  of  iron,  generally 
present  in  small  quantities  after  §  113,  p.  279. 

b.  Decomposition  by  SMITH'S  method,  p.  426.      Separate  the 
alkalies  after  §  152,  1. 

-  c.  Determine  loss  by  ignition. 

27.  ASSAY  OF  A  CALAMINE  OR  SMrrHSONTTE. 

After  §  215. 

Volumetric  determination  of  the  zinc. 

28.  ASSAY  OF  GALENA. 
Determination  of  the  lead,  as  directed  §  213. 

29.  VALUATION  OF  CHLORIDE  OF  LIME  (§  199). 

a.  After  PENOT  (p.  699). 

b.  After  OTTO  (p.  701). 

30.  VALUATION  OF  MANGANESE  (§  202). 

a.  After  FKESEXIUS  and  WILL  (p.  705).     The  evolved  CO,  to 
be  weighed  (p.  708). 

b.  After  BUNSEN  (p.  709). 

c.  By  means  of  iron  (p.  709). 


806  EXERCISES   FOB   PRACTICE. 

31.  COMPLETE  ANALYSIS  OF  IRON  ORE  (§  217). 
E.  DETERMINATION  OF  THE  SOLUBILITY  OF  SALTS. 

32.  DETERMINATION  OF  THE  DEGREE  OF  SOLUBILITY  OF  COMMON 

SALT. 

a.  At  boiling  heat. — Dissolve  perfectly  pure  pulverized  sodium 
chloride  in  distilled  water,  in  a  flask,  heat  to  boiling,  and  keep  in 
ebullition  until  part  of  the  dissolved  salt  separates.     Filter  the 
fluid  now  with  the  greatest  expedition,  through  a  funnel  surrounded 
with  boiling  water  and  covered  with  a  glass  plate,  into  an  accu- 
rately tared  capacious  measuring  flask.     As  soon  as  about  100  c.c. 
of  fluid  have  passed  into  the  flask,  insert  the  cork,  allow  to  cool, 
and  weigh.     Fill  the  flask  now  up  to  the  mark  with  water,  and 
determine  the  salt  in  an  aliquot  portion  of  the  fluid,  by  evaporating 
in  a  platinum  dish  (best  with  addition  of  some  ammonium  chloride, 
which  will,  in  some  measure,  prevent  decrepitation) ;  or  by  deter- 
mining the  chlorine  (§  141). 

b.  At  14:°. — Allow  the  boiling  saturated  solution  to  cool  down 
to  this  temperature  with  frequent  shaking,  and  then  proceed  as 
in  a. 

100  parts  of  water  dissolve  at  109*7°. . .  .40*35  of  sodium  chloride. 
100  "  "  14°     35*87  "  " 

33.  DETERMINATION  OF  THE  DEGREE  OF  SOLUBILITY  OF  CALCIUM 

SULPHATE. 

a.  At  100°. 

I.  At  12°. 

Digest  pure  pulverized  calcium  sulphate  for  some  time  with 
water,  in  the  last  stage  of  the  process  at  40° — 50°  (at  which  tempera- 
ture sulphate  of  lime  is  most  soluble)  ;  shake  the  mixture  frequently 
during  the  process.  Decant  the  clear  solution,  together  with  a 
little  of  the  precipitate,  into  two  flasks,  and  boil  the  fluid  in  one  of 
them  for  some  time ;  allow  that  in  the  other  to  cool  down  to  12°, 
with  frequent  shaking,  and  let  it  stand  for  some  time  at  that 
temperature.  Then  filter  both  solutions,  weigh  the  filtrates,  and 
determine  the  amount  of  calcium  sulphate  respectively  contained 
in  them,  by  evaporating  and  igniting  the  residues. 

100  parts  of  water  dissolve  at  100°    0'217  of  anhydrous  calcium  sulphate. 

100  "  "  12°     0-233 

34.  ANALYSIS  OF  ATMOSPHERIC  AIR. 
See  §  221. 


c  

48 

H     .     . 

6 

o 

96 

EXERCISES-  FOR   PRACTICE.  807 


F.   ORGANIC   ANALYSIS   AND   ANALYSES   IN   WHICH    ORGANIC 
ANALYSIS  IS  APPLIED. 

35.  ANALYSIS  OF  TARTARIC  ACID. 

Select  clean  and  white  crystals.     Powder  and  dry  at  100°. 

a.  Burn   with    lead    chromate   after   §  177.      For   details   of 
manipulation  see  §§  174  and  175. 

b.  Burn  with  oxygen  gas  in  a  tray,  §  178. 

32 
4 
64 

150  100 

36.  DETERMINATION   OF  THE  NITROGEN  IN  CRYSTALLIZED  POTAS- 

SIUM  FERROCYANIDE. 

Triturate  the  perfectly  pure  crystals,  press  in  blotting  paper, 
and  determine  the  nitrogen  as  directed  §  185.  (Combustion  with 
soda  lime.)  The  formula  requires  19*93  per  cent,  of  nitrogen. 

37.  ANALYSIS  OF  URIC  ACID  (or  any  other  perfectly  pure  organic 

compound  of  carbon,  hydrogen,  oxygen,  and  nitrogen). 

Dry  pure  uric  acid  at  100°. 

a.  Determination  of  the  carbon  and  hydrogen  (§  183). 

b.  Determination  of  the  nitrogen. 

a.  After  §  185. 
ft.  After  §  184,  II. 

C5 60-00  35-68 

N4 56-16  33-40* 

H4 4-00  2-38 

O, 48-00  28-54 


168-16  100-00 

38.  ANALYSIS  OF  A  SUPERPHOSPHATE  (§  220). 

39.  ANALYSIS  OF  COAL  (§  219.) 

40.  ANALYSIS  OF  A  CAST  IRON. 


After  §  218. 


*  Taking  14  for  the  atomic  weight  of  N  gives  33'33  per  cent,  of  nitrogen. 


APPENDIX, 


ANALYTICAL  EXPERIMENTS.* 

1.  ACTION  OP  WATER  UPON  GLASS  AND  PORCELAIN  VESSELS,  IN  THE; 
PROCESS  OP  EVAPORATION  (to  §  41). 

A  large  bottle  was  filled  with  water  cautiously  distilled  from  a  copper  boiler 
with  a  tin  condensing  tube.  All  the  experiments  in  1  were  made  with  this 
water. 

a.  300  c.c.,  cautiously  evaporated  in  a  platinum  dish,  left  a  residue  weighing, 
after  ignition,  0*0005  grm. =0*0017  per  1000. 

b.  600  c.c.  were  evaporated,  boiling,  nearly  to  dryness,  in  a  wide  flask  of 
Bohemian  glass ;  the  residue  was  transferred  to  a  platinum  dish,  and  the  flask 
rinsed  with  100  c.c.  distilled  water,  which  was  added  to  the  residue  in  the  dish ; 
the  fluid  in  the  latter  was  then  evaporated  to  dryness,  and  the  residue  ignited. 

The  residue  weighed 0'0104  gnn. 

Deducting  from  this  the  quantity  of  fixed  matter  originally 
contained  in  the  distilled  water,  viz ..  0'0012     " 


There  remains  substance  taken  up  from  the  glass 0'0092     " 

=0-0153  per  1000. 

In  three  other  experiments,  made  in  the  same  manner,  300  c.c.  left,  in  two 
0-0049  grm.,  in  the  third  0'0037  grm. ;  which,  calculated  for  600  c.c.,  gives  art 

average  of 0'0090  grm. 

And  after  a  deduction  of ..0-0012     " 


0-0078     " 
=0-013  per  1000. 

We  may  therefore  assume  that  1  litre  of  water  dissolves,  when  boiled  down- 
to  a  small  bulk  in  glass  vessels,  about  14  milligrammes  of  the  constituents  of  the- 
glass. 

c.  600  c.c.  were  evaporated  nearly  to  dryness  in  a  dish  of  Berlin  porcelain,  and 
in  all  other  respects  treated  as  in  b. 

The  residue  weighed 0*0015  grm. 

Deducting  from  this  the  quantity  of  fixed  matter  contained  in 
the  distilled  water,  viz 0'0012     " 

There  remains  substance  taken  up  from  the  porcelain 0*0003     " 

=0-0005  per  1000. 

*  The  experiments  are  numbered  as  in  the  original  edition,  but  some  are  omitted. 


810  ANALYTICAL   EXPERIMENTS. 

2.  ACTION  OF  HYDROCHLORIC,  ACID  UPON  GLASS  AND  PORCELAIN  VESSELS, 
IN  THE  PROCESS  OF  EVAPORATION  (to  §  41). 

The  distilled  water  used  in  1  was  mixed  with  y1^  of  pure  hydrochloric  acid. 

a.  300  grin.,  evaporated  in  a. platinum  dish,  left  0'002  grm.  residue. 

b.  300  grm.,  evaporated  first  in  Bohemian  glass  nearly  to  dryness,  then  in  a 
platinum  dish,  left  0*0019  residue;  the  dilute  hydrochloric  acid,  therefore,  had 
not  attacked  the  glass. 

c.  300  grm.,  evaporated  in  Berlin  porcelain,  &c.,  left  0*0036  grm.,  accordingly 
after  deducting  0-002,  0-0016=0 '0053  per  1000. 

d.  In  a  second  experiment  made  in  the  same  manner  as  in  c.,  the  residue 
amounted  to  0'0034,  accordingly  after  deducting  0*002,  0 '0014=0-0047  per  1000. 

Hydrochloric  acid,  therefore,  attacks  glass  much  less  than  water,  whilst 
porcelain  is  about  equally  affected  by  water  and  dilute  hydrochloric  acid.  This 
shows  that  the  action  of  water  upon  glass  consists  in  the  formation  of  soluble 
basic  silicates. 

3.  ACTION    OF    SOLUTION   OF   AMMONIUM    CHLORIDE    UPON    GLASS  AND 
PORCELAIN  VESSELS,  IN  THE  PROCESS  OF  EVAPORATION  (to  §  41). 

In  the  distilled  water  of  1,  ^  of  ammonium  chloride  was  dissolved,  and  the 
solution  filtered. 

a.  300  c.c.,  evaporated  in  a  platinum  dish,  left  O'OOG  grm.  fixed  residue. 

b.  300  c.c.,  evaporated  first  nearly  to  dryness  in  Bohemian  glass,  then  to  dry 
ness  in  a  platinum  dish,  left  0'0179  grm. ;  deducting  from  this  0*006  grm.,  there 
remains  substance  taken  up  from  the  glass,  0-0119=0-0397  per  iOOO. 

c.  300  c.c.,  treated  in  the   same  manner  in  Berlin  porcelain,  left  0-0178 
deducting  from  this  0'006,  there  remains  0-0118=0-0393  per  1000. 

Solution  of  ammonium  chloride,  therefore,  strongly  attacks  both  glass  and 
porcelain  in  the  process  of  evaporation. 

4.  ACTION  OF  SOLUTION  OF  SODIUM  CARBONATE  UPON  GLASP  AND  PORCE- 
LAIN VESSELS  (to  §  41). 

In  the  distilled  water  of  1,  TV  of  pure  crystallized  sodium  carbonate  was  dis- 
solved. 

a.  300  c.c.,  supersaturated  with  hydrochloric  acid  and  evaporated  to  dryness 
in  a  platinum  dish,  &c.,  gave  0'0026  grm.  silica=0'0087  per  1000. 

b.  300  c.c.  were  gently  boiled  for  three  hours  in  a  glass  vessel,  the  evaporat- 
ing water  being  replaced  from  time  to  time;  the  tolerably  concentrated  liquid 
was  then  treated  as  in  a;  it  left  a  residue  weighing  0'1376  grm. ;  deducting  from 
this  the  0-0026  grm.  left  in  a,  there  remains  0  135  grm.  =0  450  per  1000. 

c.  300  c.c.,  treated  in  the  same  manner  as  in  b,  in  a  porcelain  vessel,   left 
0-0099;  deducting  from  this  0*0026  grm.,  there  re  mains  0-0073=0-0243  per  1000. 

Which  shows  that  boiling  solution  of  sodium  carbonate  attacks  glass  very 
strongly,  and  porcelain  also  in  a  very  marked  manner. 

5.  WATER  DISTILLED  FROM  GLASS  VESSELS  (to  §  56,  1). 

42'41  grm.  of  water  distilled  with  extreme  caution  from  a  tall  flask  with  a 
LIEBIG'S  condenser,  left  upon  evaporation  in  a  platinum  dish,  a  residue  weighing, 
after  ignition,  O'OOIS  grm.,  consequently 


ANALYTICAL    EXPERIMENTS.  811 

6.  POTASSIUM  SULPHATE  AND  ALCOHOL  (to  §  68,  a). 

a.  Ignited  pure  potassium  sulphate  was  digested  cold  with  absolute  alcohol, 
for  several  days,  with  frequent  shaking;  the  fluid  was  filtered  off,  the  filtrate 
diluted  with  water,  and  then  mixed  with  barium  chloride.     It  remained  perfectly 
clear  upon  the  addition  of  this  reagent,  but  after  the  lapse  of  a  considerable  tune 
it  began  to  exhibit  a  slight  opalescence.     Upon  evaporation  to  dryness,  there 
remained  a  very  trifling  residue,  which  gave,  however,  distinct  indications  of  the 
presence  of  sulphuric  acid. 

b.  The  same  salt  treated  in  the  same  manner,  with  addition  of  some  pure 
concentrated  sulphuric  acid,  gave  a  filtrate  which,  upon  evaporation  in  a  plati- 
num dish,  left  a  clearly  perceptible  fixed  residue  of  potassium  sulphate. 

7.  DEPORTMENT  OF  POTASSIUM   CHLORIDE  IN   THE  AIR  AND  AT  A  HIGH 

TEMPERATURE  (to  §  68,  b). 

(V9727  grm.  of  ignited  (not  fused)  pure  potassium  chloride,  heated  for  10 
minutes  to  dull  redness  in  an  open  platinum  dish,  lost  0'0007  grm.;  the  salt  was 
then  kept  for  10  minutes  longer  at  the  same  temperature,  when  no  further  dimi- 
nution of  weight  was  observed.  Heated  to  bright  redness  and  semi-fusion,  the 
salt  suffered  a  further  loss  of  weight  to  the  extent  of  0'0009  grm.  Ignited 
intensely  and  to  perfect  fusion,  it  lost  0-0034  grm.  more. 

Eighteen  hours'  exposure  to  the  air  produced  not  the  slightest  increase  of 
weight. 

8.  SOLUBILITY  OF  POTASSIUM  PLATINIC  CHLORIDE  IN  ALCOHOL  (to  §  68,  c). 
a.  In  absence  of  free  Hydrochloric  Acid. 

a.  An  excess  of  perfectly  pure,  recently  precipitated  potassium  platinic 
chloride  was  digested  for  6  days  at  15 — 20°,  with  alcohol  of  97%5  per  cent.,  in  a 
stoppered  bottle,  with  frequent  shaking.  72'5  grm.  of  the  perfectly  colorless 
filtrate  left  upon  evaporation  in  a  platinum  dish  a  residue  which,  dried  at  100°, 
weighed  0'006  grm.;  1  part  of  the  salt  requires  therefore  12083  parts  of  alcohol 
of  97'5  per  cent,  for  solution. 

ft.  The  same  experiment  was  made  with  alcohol  of  76  per  cent.  The  filtrate 
might  be  said  to  be  colorless;  upon  evaporation,  slight  blackening  ensued,  on 
which  account  the  residue  was  determined  as  platinum.  75 '5  grm.  yielded 
O'OOS  grm.  platinum,  corresponding  to  0'02  grm.  of  the  salt.  One  part  of  the 
salt  dissolves  accordingly  in  3775  parts  of  alcohol  of  76  per  cent. 

y.  The  same  experiment  was  made  with  alcohol  of  55  per  cent.     The  filtrate 
was  distinctly  yellowish.     63'2  grm.  left  0"0241  grm.  platinum,  corresponding  to 
0'06  grm.  of  the  salt.     One  part  of  the  salt  dissolves  accordingly  in  1053  parts  of 
alcohol  of  55  per  cent. 
b.  In  presence  of  free  Hydrochloric  Acid. 

Recently  precipitated  potassium  platinic  chloride  was  digested  cold  with 
alcohol  of  76  per  cent. ,  to  which  some  hydrochloric  acid  had  been  added.  The 
solution  was  yellowish;  67  grm.  left  0'0146  grm.  platinum,  which  corresponds  to 
0-0365  grm.  of  the  salt.  One  part  of  the  salt  dissolves  accordingly  in  1835  parts 
of  alcohol  mixed  with  hydrochloric  acid. 

9.  SODIUM  SULPHATE  AND  ALCOHOL  (to  §  69,  a). 

Experiments  made  with  pure  anhydrous  sodium  sulphate,  in  the  manner 


812  ANALYTICAL   EXPERIMENTS. 

described  in  6,  showed  that  this  salt  comports  itself  both  with  pure  alcohol,  and 
with  alcohol  containing  sulphuric  acid,  exactly  like  potassium  sulphate. 

10.  DEPORTMENT  OP  IGNITED  SODIUM  SULPHATE  IN  THE  Am  (to  §  69,  a). 

25169  grm.  anhydrous  sodium  sulphate  were  exposed,  in  a  watch-glass,  to 
the  open  air  on  a  hot  summer  day.  The  first  few  minutes  passed  without  any 
increase  of  weight,  but  after  the  lapse  of  5  hours  there  was  an  increase  of  0*0061 
grm. 

12.  DEPORTMENT  OF  SODIUM  CHLORIDE  IN  THE  AIR  (to  §  69,  b). 

4-3281  grm.  of  chemically  pure,  moderately  ignited  (not  fused)  sodium 
chloride,  which  had  been  cooled  under  a  bell-glass  over  sulphuric  acid,  acquired 
during  45  minutes'  exposure  to  the  (somewhat  moist)  air  an  increase  of  weight 
of  0-0009  grm. 

13.  DEPORTMENT   OP   SODIUM   CHLORIDE  UPON  IGNITION  BY  ITSELF  AND 
WITH  AMMONIUM  CHLORIDE  (to  §  69,  b). 

4*3281  grm.  chemically  pure,  ignited  sodium  chloride  were  dissolved  in 
water,  in  a  moderate-sized  platinum  dish,  and  pure  ammonium  chloride  was 
added  to  the  solution,  which  was  then  evaporated  and  the  residue  gently  heated 
until  the  evolution  of  ammonium  chloride  fumes  had  apparently  ceased.  The 
residue  weighed  4 '3334  grm.  It  was  then  very  gently  ignited  for  about  2  minutes, 
and  after  this  re-weighed,  when  the  weight  was  found  to  be  4*3314  grm.  A  few 
minutes'  ignition  at  a  red  heat  reduced  the  weight  to  4*3275  grm.,  and  2  minutes' 
further  ignition  at  a  bright  red  heat  (upon  which  occasion  white  fumes  were 
seen  to  escape),  to  4 '3249  grm. 

14.  DEPORTMENT  OF  SODIUM  CARBONATE  IN  THE  AIR  AND  ON  IGNITION 
(to  §  69,  c). 

2*1061  grm.  of  moderately  ignited  chemically  pure  sodium  carbonate  were 
exposed  to  the  air  in  an  open  platinum  dish  in  July  in  bad  weather;  after  10 
minutes  the  weight  was  2-1078,  after  1  hour,  21113,  after  5  hours,  2-1257. 

1  -4212  grm.  of  moderately  ignited  chemically  pure  sodium  carbonate  were 
ignited  for  5  minutes  in  a  covered  platinum  crucible ;  no  fusion  took  place,  and 
the  weight  was  unaltered.  Heated  more  strongly  for  5  minutes,  it  partially 
fused,  and  then  weighed  1*4202.  After  being  kept  fusing  for  5  minutes,  it 
•weighed  1-4135. 

15.  DEPORTMENT    OF    AMMONIUM    CHLORIDE    UPON   EVAPORATION   AND 
DRYING  (to  §  70,  a). 

0"5625  grm.  pure  and  perfectly  dry  ammonium  chloride  was  dissolved  in 
water  in  a  platinum  dish,  evaporated  to  dryness  in  the  water-bath  and  com- 
pletely dried;  the  weight  was  now  found  to  be  0'5622  grm.  (ratio  100:99'94).  It 
was  again  heated  for  15  minutes  in  the  water-bath,  and  afterwards  re-weighed, 
when  the  weight  was  found  to  be  0'5612  grm.  (ratio  100:99-77).  Exposed  once 
more  for  15  minutes  to  the  same  temperature,  the  residue  weighed  0'5608  grm. 
(ratio  100:99-69). 

16.  SOLUBILITY  OF  AMMONIUM  PLATINIC  CHLORIDE  IN  ALCOHOL  (to  §  70,  6). 
a.  In  absence  of  free  Hydrochloric  Acid. 

a.  An  excess  of  perfectly  pure,   recently  precipitated   ammonium  platinic 


ANALYTICAL   EXPERIMENTS.  813 

chloride  was  digested  for  6  days,  at  15 — 20°,  with  alcohol  of  97'5  per  cent.,  in  a 
stoppered  bottle,  with  frequent  agitation. 

74'3  grm.  of  the  perfectly  colorless  nitrate  left,  upon  evaporation  and  ignition 
in  a  platinum  dish,  O0012  grm.  platinum,  corresponding  to  0'0028  of  the  salt. 
One  part  of  the  salt  requires  accordingly  26535  parts  of  alcohol  of  97*5  per  cent. 

ft.  The  same  experiment  was  made  with  alcohol  of  76  per  cent.  The  filtrate 
was  distinctly  yellowish. 

81 '75  grm.  left  0'0257  platinum,  which  corresponds  to  0-0584  grm.  of  the  salt. 
One  part  of  the  salt  dissolves  accordingly  in  1406  parts  of  alcohol  of  76  per  cent. 

y.  The  same  experiment  was  made  with  alcohol  of  55  per  cent.  The  filtrate 
was  distinctly  yellow.  Slight  blackening  ensued  upon  evaporation,  and  56 '5 
grm.  left  0'0364  platinum,  which  corresponds  to  0'08272  grm.  of  the  salt.  Con- 
sequently, 1  part  of  the  salt  dissolves  in  665  parts  of  alcohol  of  55  per  cent. 

b.  In  presence  of  Hydrochloric  Acid. 

The  experiment  described  in  ft  was  repeated,  with  this  modification,  that 
some  hydrochloric  acid  was  added  to  the  alcohol.  76'5  grm.  left  0'0501  grm.  of 
platinum,  which  corresponds  to  0'1139  grm.  of  the  salt.  672  parts  of  the  acidi- 
fied alcohol  had  therefore  dissolved  1  part  of  the  salt. 

17.  SOLUBILITY  OF  BARIUM  CARBONATE  IN  WATER  (to  §  71,  b). 

a.  In  Cold  Water. — Perfectly  pure,  recently  precipitated  Ba  CO3  was  digested 
for  5  days  with  water  of  16 — 20°,  with  frequent  shaking.     The  mixture  was 
filtered,  and  a  portion  of  the  filtrate  tested  with  sulphuric  acid,  another  portion 
with  ammonia;  the  former  reagent  immediately  produced  turbidity  in  the  fluid, 
the  latter  only  after  the  lapse  of  a  considerable  time.     84*82  grm.  of  the  solution 
left,  upon  evaporation,  0'0060  Ba  CO3.     One  part  of  that  salt  dissolves  conse- 
quently in  14137  parts  of  cold  water. 

b.  In  Hot  Water. — The  same  barium  carbonate  being  boiled  for  10  minutes 
with  pure  distilled  water,  gave  a  filtrate  manifesting  the  same  reactions  as  that 
prepared  with  cold  water,  and  remaining  perfectly  clear  upon  cooling.     84 '82 
grm.  of  the  hot  solution  left,  upon  evaporation,  0'0055  grm.  of  barium  carbonate. 
One  part  of  that  salt  dissolves  therefore  in  15421  parts  of  boiling  water. 

18.  SOLUBILITY  OF  BARIUM  CARBONATE  IN  WATER  CONTAINING  AMMONIA 
AND  AMMONIUM  CARBONATE  (to  §  71,  b). 

A  solution  of  chemically  pure  barium  chloride  was  mixed  with  ammonia  and 
ammonium  carbonate  in  excess,  gently  heated  and  allowed  to  stand  at  rest  for  12 
hours;  the  fluid  was  then  filtered  off;  the  filtrate  remained  perfectly  clear  upon 
addition  of  sulphuric  acid;  but  after  the  lapse  of  a  very  considerable  time,  a 
hardly  perceptible  precipitate  separated.  84 '82  grm.  of  the  filtrate  left,  upon 
evaporation  in  a  small  platinum  dish,  and  subsequent  gentle  ignition,  0'0006 
grm.  One  part  of  the  salt  had  consequently  dissolved  in  141000  parts  of  the 
fluid. 

19.  SOLUBILITY  OF  BARIUM  SILICO-FLUORIDE  IN  WATER  (to  §  71,  c). 

a.  Recently  precipitated,  thoroughly  washed  barium  silico-fluoride  was 
digested  for  4  days  in  cold  water,  with  frequent  shaking;  the  fluid  was  then 
filtered  off,  and  a  portion  of  the  filtrate  tested  with  dilute  sulphuric  acid,  another 


814  ANALYTICAL   EXPERIMENTS. 

portion  with  solution  of  calcium  sulphate ;  both  reagents  produced  turbidity — 
the  former  immediately,  the  latter  after  one  or  two  seconds — precipitates  sepa- 
rated from  both  portions  after  the  lapse  of  some  time.  84.82  grm.  of  the  filtrate 
left  a  residue  which,  after  being  thoroughly  dried,  weighed  0-0223  grm.  One 
part  of  the  salt  had  consequently  required  3802  parts  of  cold  water  for  its  solu- 
tion. 

b.  A  portion  of  another  sample  of  recently  precipitated  barium  silico-fluoride 
was  heated  with  water  to  boiling,  and  the  solution  allowed  to  cool  (upon  which 
a  portion  of  the  dissolved  salt  separated).  The  cold  fluid  was  left  for  a  consider- 
able time  longer  in  contact  with  the  undissolved  salt,  and  was  then  filtered  off. 
The  filtrate  showed  the  same  deportment  with  solution  of  sulphate  of  lime  as 
that  of  a.  84-82  grm.  of  it  left  0  '025  grm.  One  part  of  the  salt  had  accordingly 
dissolved  in  3392  parts  of  water. 

20.  SOLUBILITY  OF  BARIUM  SILICO-FLUORIDE  IN  WATER  ACIDIFIED  WITH 
HYDROCHLORIC  ACID  (to  §  71,  c). 

a.  Recently  precipitated  pure  barium  silico-fluoride  was  digested  with  frequent 
agitation  for  3  weeks  with  cold  water  acidified  with  hydrochloric  acid.     The 
filtrate  gave  with  sulphuric  acid  a  rather  copious  precipitate.     84'82  grm.  left 
01155  grm.  of  thoroughly  dried  residue,  which,  calculated  as  barium  silico- 
fluoride,  gives  733  parts  of  fluid  to  1  part  of  that  salt. 

b.  Recently  precipitated  pure  barium  silico-fluoride  was  mixed  with  water 
very  slightly  acidified  with  hydrochloric  acid,  and  the  mixture  heated  to  boiling. 
Cooled  to  12°,  84-82  grm.  of  the  filtrate  left  a  residue  of  0*1322  grm.,  which  gives 
640  parts  of  fluid  to  1  part  of  the  salt. 

N.B.  The  solution  of  barium  silico-fluoride  in  hydrochloric  acid  is  not  effected 
without  decomposition;  at  least,  the  residue  contained,  even  after  ignition,  a 
rather  large  proportion  of  barium  chloride. 

21.  SOLUBILITY  OF  STRONTIUM  SULPHATE  IN  WATER  (to  §  72,  a). 

a.  In  Water  of  14°. 

84 '82  grm.  of  a  solution  prepared  by  4  days'  digestion  of  recently  precipitated 
strontium  sulphate  with  water  at  the  common  temperature,  left  0'0123  grm.  of 
strontium  sulphate.  One  part  of  strontium  sulphate  dissolves  consequently  in 
6895  parts  of  water. 

b.  In  Water  of  100°. 

84 '82  grm.  of  a  solution  prepared  by  boiling  recently  precipitated  strontium 
sulphate  several  hours  with  water,  left  0'0088  grm.  Consequently  1  part  of 
strontium  sulphate  dissolves  in  9638  parts  of  boiling  water. 

22.  SOLUBILITY  OF  STRONTIUM  SULPHATE  IN  WATER  CONTAINING  HYDRO- 
CHLORIC ACID  AND  SULPHURIC  ACID  (to  §  72,  a). 

a.  84'82  grm.  of  a  solution  prepared  by  3  days'  digestion,  left  0'0077  grm. 
SrSO4. 

b.  42-41  grm.  of  a  solution  prepared  by  4  days'  digestion,  left  0-0036  grm. 

c.  Pure  strontium  carbonate  was  dissolved  in  an  excess  of  hydrochloric  acid, 
and  the  solution  precipitated  with  an  excess  of  sulphuric  acid  and  then  allowed 
to  stand  in  the  cold  for  a  fortnight.     84*82  grm.  of  the  filtrate  left  0'0066  grm. 


ANALYTICAL    EXPERIMENTS.  815 

In  a.  I  part    of   SrSO4  required  11016  parts. 

b.  1  "  ".       11780      " 

c.  1  "  "        12791      " 


Mean 11862  parts. 

23.  SOLUBILITY  OF  STRONTIUM  SULPHATE  IN  DILUTE  NITRIC  Aero,  HYDRO- 
CHLORIC ACID,  AND  ACETIC  ACID  (to  §  72,  a). 

a.  Recently  precipitated  pure  strontium  sulphate  was  digested  for  2  days  in 
the  cold  with  nitric  acid  of  4*8  per  cent.     150  gun.  of  the  nitrate  left  0*3431  grm. 
One  part  of  the  salt  required  accordingly  435  parts  of  the  dilute  acid  for  its 
solution ;  in  another  experiment  i  part  of  the  salt  was  found  to  require  429  parts 
of  the  dilute  acid.     Mean,  432  parts. 

b.  The  same. salt  was  digested  for  2  days  in  the  cold  with  hydrochloric  acid 
'of  8*5  per  cent.     100  grm.  left  0*2115,  and  in  another  experiment,  0'2104grm. 

One  part  of  the  salt  requires,  accordingly,  in  the  mean,  474  parts  of  hydrochloric 
acid  of  8*5  per  cent,  for  its  solution. 

c.  The  same  salt  was  digested  for  2  days  in  the  cold  with  acetic  acid  of  15  '6 
per  cent.  C2H4O2.     100  gnn.  left  0*0126,  and  in  another  experiment,  0*0129  grm. 
One  part  of  the  salt  requires,  accordingly,  in  the  mean,  7843  parts  of  acetic  acid 
of  15*6  per  cent. 

24.  SOLUBILITY  OF  STRONTIUM  CARBONATE  m  COLD  WATER  (to  §  72,  b). 

Recently  precipitated,  thoroughly  washed  strontium  carbonate  was  digested 
several  days  with  cold  distilled  water,  with  frequent  shaking.  84*82  grm.  of  the 
filtrate  left,  upon  evaporation,  a  residue  weighing,  after  ignition,  0*0047  grni. 
One  part  of  strontium  carbonate  requires  therefore  18045  parts  of  water  for  its 
solution. 

25.  SOLUBILITY  OF  STRONTIUM  CARBONATE  IN  WATER  CONTAINING  AMMONIA. 
AND  AMMONIUM  CARBONATE  (to  §  72,  b). 

Recently  precipitated,  thoroughly  washed  strontium  carbonate  was  digested 
for  4  weeks  with  cold  water  containing  ammonia  and  ammonium  carbonate, 
with  frequent  shaking.  84*82  grm.  of  the  filtrate  left  0*0015  grm.  SrCO3. 
Consequently,  1  part  of  the  salt  requires  56545  parts  of  this  fluid  for  its  solution. 

If  solution  of  strontium  chloride  is  precipitated  with  ammonium  carbonate 
and  ammonia  as  directed  §  102,  2,  a,  sulphuric  acid  produces  no  turbidity  in  the 
filtrate,  after  addition  of  alcohol. 

26.  SOLUBILITY  OF  CALCIUM  CARBONATE  LN  COLD  AND  IN  BOILING  WATER 
(to  §  73,  b). 

a.  A  solution  prepared  by  boiling  as  in  26,  b,  was  digested  in  the  cold  for  4 
weeks,  with  frequent  agitation,  with  the  undissolved  precipitate.     84*82  grm. 
left  0*0080  CaCO3.     One  part  therefore  required  10601  parts. 

b.  Recently  precipitated  calcium  carbonate  was  boiled  for  some  time  with 
distilled  water.      42*41  grm.  of  the  filtrate  left,  upon  evaporation  and  gentle 
ignition  of  the  residue,  0*0048  CaCO3.     One  part  requires  consequently  8834 
parts  of  boiling  water. 


S16  ANALYTICAL   EXPERIMENTS. 

27.  SOLUBILITY  OF  CACO3  IN  WATER  CONTAINING  AMMONIA  AND  AMMO- 
NIUM CARBONATE  (to  §  73,  b). 

Pure  dilute  solution  of  calcium  chloride  was  precipitated  with  ammonium 
carbonate  and  ammonia,  allowed  to  stand  24  hours,  and  then  filtered.  84 '82 
grm.  left  0*0013  grm.  Ca  CO3.  One  part  requires  consequently  65246  parts. 

28.  DEPORTMENT  OF  CALCIUM  CARBONATE  UPON  IGNITION  IN  A  PLATINUM 
CRUCIBLE  (to  §  73,  b). 

0'7955  grm.  of  perfectly  dry  calcium  carbonate  was  exposed,  in  a  small  and 
thin  platinum  crucible,  to  the  gradually  increased  and  finally  most  intense  heat 
of  a  good  BERZELIUS'  lamp.  The  crucible  was  open  and  placed  obliquely. 
After  the  first  15  minutes  the  mass  weighed  0'6482 — after  half  an  hour  0'6256 — 
after  one  hour  0*5927,  which  latter  weight  remained  unaltered  after  15  minutes' 
additional  heating.  This  corresponds  to  74 '5  per  cent.,  whilst  the  proportion  of 
CaO  in  the  carbonate  is  calculated  at  56  per  cent. ;  there  remained  therefore 
evidently  still  a  considerable  amount  of  the  carbonic  acid. 

29.  COMPOSITION  OF  CALCIUM  OXALATE  DRIED  AT  100°  (to  §  73,  c). 

0'8510  grm.  of  thoroughly  dry  pure  calcium  carbonate  was  dissolved  in 
hydrochloric  acid;  the  solution  was  precipitated  with  ammonium  oxalate  and 
ammonia,  and  the  precipitate  collected  upon  a  weighed  filter  and  dried  at  100°, 
until  the  weight  remained  constant.  The  calcium  oxalate  so  produced  weighed 
1  -2461  grm.  Calculating  this  as  CaC2O4  +  H2O,  the  amount  found  contained 
0-4772  CaO,  which  corresponds  to  56 '07  per  cent,  in  the  calcium  carbonate;  the 
calculated  proportion  of  CaO  in  the  latter  is  56  per  cent. 

30.  DEPORTMENT  OF  MAGNESIUM  SULPHATE  IN  THE  AIR  AND  UPON  IGNI- 
TION (to  §  74,  a). 

0'8135  grm.  of  perfectly  pure  anhydrous  MgSO4  in  a  covered  platinum 
crucible  acquired,  on  a  fine  and  warm  day  in  June,  in  half  an  hour,  an  increase 
of  weight  of  0'004  grm.,  and  in  the  course  of  12  hours,  of  0'067  grm.  The  salt 
could  not  be  accurately  weighed  in  the  open  crucible,  owing  to  continual  increase 
of  weight. 

0'8135  grm.,  exposed  for  some  time  to  a  very  moderate  red  heat,  suffered  no 
diminution  of  weight ;  but  after  5  minutes'  exposure  to  an  intense  red  heat,  the 
substance  was  found  to  have  lost  0'0075  grm'. ,  and  the  residue  gave  no  longer  a 
clear  solution  with  water.  About  0'2  grm.  of  pure  magnesium  sulphate  exposed 
in  a  small  platinum  crucible,  for  15  to  20  minutes,  to  the  heat  of  a  powerful 
blast  gas  lamp,  gave,  with  dilute  hydrochloric  acid,  a  solution  in  which  barium 
chloride  failed  to  produce  the  least  turbidity. 

31.  SOLUBILITY  OF  AMMONIUM  MAGNESIUM  PHOSPHATE  IN  PURE  WATER 
(to  §  74,  ft). 

a.  Recently  precipitated  ammonium  magnesium  phosphate  was  thoroughly 
washed  with  water,  then  digested  for  24  hours  with  water  of  about  15°,  with 
frequent  shaking. 

84-42  grm.  of  the  filtrate  left . . ; 0'0047  grm. 

of  magnesium  pyrophosphate. 


ANALYTICAL   EXPERIMENTS.  817 

b.  The  same  precipitate  was  digested  in  the  same  manner  for  72 
hours. 

84-42  grm.  of  the  filtrate  left 0-0043     " 

Mean 0'0045     " 

which  corresponds  to  0*00552  grm.  of  the  anhydrous  double  salt.     One  part  of 
that  salt  dissolves  therefore  in  15293  parts  of  pure  water. 

The  cold  saturated  solution  gave,  with  ammonia,  after  the  lapse  of  a  short 
time,  a  distinctly  perceptible  crystalline  precipitate; — on  the  addition  of  sodium 
phosphate,  it  remained  perfectly  clear,  and  even  after  the  lapse  of  2  days  no 
precipitate  had  formed;— ammonium  sodium  phosphate  produced  a  precipitate 
as  large  as  that  by  ammonia. 

32.  SOLUBILITY  OF  AMMONIUM  MAGNESIUM  PHOSPHATE  IN  WATER  CON- 
TAINING AMMONIA  (to  §  74,  b). 

a.  Pure  ammonium  magnesium  phosphate  was  dissolved  in  the  least  possible 
amount  of  nitric  acid ;  a  large  quantity  of  water  was  added  to  the  solution,  then 
ammonia  in  excess.     The  mixture  was  allowed  to  stand  at  rest  for  24  hours, 
then  filtered;  its  temperature  was  14°.     84 '42  grm.  left  O'OOIS  magnesium  pyro- 
phosphate,  which  corresponds  to  0 '00184  of  the  anhydrous  double  salt.     Conse- 
quently 1  part  of  the  latter  requires  45880  parts  of  ammoniated  water  for  its 
solution. 

b.  Pure  ammonium  magnesium  phosphate  was  digested  for  4  weeks  with 
ammoniated  water,  with  frequent  shaking;  the  fluid  (temperature  14°)  was  then 
filtered  off;  126 '63  grm.  left  0'0024  magnesium  pyrophosphate,  which  corresponds 
to  0-00296  of  the  double  salt.     One  part  of  it  therefore  dissolves  in  42780  parts  of 
ammoniated  water.     Taking  the  mean  of  a  and  b,  1  part  of  the  double  salt 
requires  44330  parts  of  ammoniated  water  for  its  solution. 

33.  ANOTHER  EXPERIMENT  ON  THE  $AME  SUBJECT  (to  §  74,  b). 

Recently  precipitated  ammonium  magnesium  phosphate,  most  carefully 
washed  with  water  containing  ammonia,  was  dissolved  in  water  acidified  with 
hydrochloric  acid,  ammonia  added  in  excess,  and  allowed  to  stand  in  the  cold 
for  24  hours.  169 -64  grm.  of  the  filtrate  left  0'0031  magnesium  pyrophosphate, 
corresponding  to  0'0038  of  anhydrous  ammonium  magnesium  phosphate.  One 
part  of  the  double  salt  required  therefore  44600  parts  of  the  fluid. 

34.  SOLUBILITY  OF  AMMONIUM   MAGNESIUM  PHOSPHATE   m  WATER  CON- 
TAINING AMMONIUM  CHLORIDE  (to*  §  74,  b). 

Recently  precipitated,  thoroughly  washed  ammonium  magnesium  phosphate 
was  digested  in  the  cold  with  a  solution  of  1  part  of  ammonium  chloride  in  5 
parts  of  water.  18 '4945  grm.  of  the  filtrate  left  0  "002  magnesium  pyrophosphate, 
which  corresponds  to  0 '00245  of  the  double  salt.  One  part  of  the  salt  dissolves 
therefore  in  7548  parts  of  the  fluid. 

35.  SOLUBILITY  OF  AMMONIUM   MAGNESIUM   PHOSPHATE  IN  WATER  CON- 
TAINING AMMONIA  AND  AMMONIUM  CHLORIDE  (to  §  74,  6). 

Recently  precipitated,  thoroughly  washed  ammonium  magnesium  phosphate 
was  digested  in  the  cold  with  a  solution  of  1  part  of  ammonium  chloride  in  7 
parts  of  ammoniated  water.  23 1283  grm.  of  the  filtrate  left  0'0012  magnesium 


818  ANALYTICAL    EXPERIMENTS. 

pyrophosphate,  which  corresponds  to  0 '00148  of  the  double  salt.     One  part  of 
the  double  salt  requires  consequently  15627  parts  of  the  fluid  for  its  solution. 

36.  DEPORTMENT   OF  ACID   SOLUTIONS  of  MAGNESIUM  PYROPHOSPHATE 
WITH  AMMONIA  (to  §  74,  c). 

0'3985  grm.  magnesium  pyrophosphate  was  treated  for  several  hours,  at  a  high 
temperature,  with  concentrated  sulphuric  acid.  This  exercised  no  perceptible 
action.  It  was  only  after  the  addition  of  some  water  that  the  salt  dissolved. 
The  fluid,  heated  for  some  time,  gave,  upon  addition  of  ammonia  in  excess,  a 
crystalline  precipitate,  which  was  filtered  off  after  18  hours;  the  quantity  of 
magnesium  pyrophosphate  obtained  was  0'3805  grm.,  that  is,  95 '48  per  cent. 
Sodium  phosphate  produced  in  the  filtrate  a  trifling  precipitate,  which  gave 
0*0150  grm.  of  magnesium  pyrophosphate,  that  is,  3*76  per  cent. 

0-3565  grm.  magnesium  pyrophosphate  was  dissolved  in  3  grm.  nitric  acid, 
of  1-2  sp.  gr. ;  the  solution  was  heated,  diluted,  and  precipitated  with  ammonia: 
the  quantity  of  magnesium  pyrophosphate  obtained  amounted  to  0'3485  grm., 
that  is,  98 '42  per  cent.;  0"4975  grm.  was  treated  in  the  same  manner  with  7'6 
grm.  of  the  same  nitric  acid:  the  quantity  re-obtained  was  0'4935  grm.,  that  is, 
99 '19  per  cent. 

0'786  grm.  treated  in  the  same  manner  with  16 '2  grm.  of  nitric  acid,  gave 
Q'7765  grm.,  that  is,  98'79  per  cent. 

The  result  of  these  experiments  may  be  tabulated  thus: 

Proportion  of  Mg2P2O 

to  nitric  acid.  Re-obtained.  Loss. 

1:    9  98-42  per  cent.  1-58 

1  :  15  99-19      "  0-81 

1  :  20  98-79      "  1'21 

37.  SOLUBILITY  OF  PURE  MAGNESIA  IN  WATER  (to  §  74,  d). 
a.  In  Cold  Water. 

Perfectly  pure  well-crystallized  magnesium  sulphate  was  dissolved  in  water, 
and  the  solution  precipitated  with  ammonium  carbonate  and  caustic  ammonia ; 
the  precipitate  was  thoroughly  washed — in  spite  of  which  it  still  retained  a  per- 
ceptible trace  of  sulphuric  acid — then  dissolved  in  pure  nitric  acid,  an  excess  of 
acid  being  carefully  avoided.  The  solution  was  then  re-precipitated  with  ammo- 
nium carbonate  and  caustic  ammonia,  and  the  precipitate  thoroughly  washed. 
The  so-prepared  perfectly  pure  magnesium  carbonate  was  ignited  in  a  platinum 
crucible  until  the  weight  remained  constant.  The  residuary  pure  magnesia  was 
then  digested  in  the  cold  for  24  hours  with  distilled  water,  with  frequent  shaking. 
The  distilled  water  used  was  perfectly  free  from  chlorine,  and  left  no  fixed 
residue  upon  evaporation. 

a.  84*82  grm.  of  the  filtrate,  cautiously  evaporated  in  a  platinum  dish,  left  a 
residue  weighing,  after  ignition,  0*0015  grm.  One  part  of  the  pure  magnesia 

dissolved  therefore  in 56546 

parts  of  cold  water. 

The  digestion  was  continued  for  48  hours  longer,  when 

(3.  84-82  grm.  left  0'0016  grm.     One  part  required  therefore 53012 

y.  84-82  grm.  left  0-0015  grm.     One  part  required 56546 

Average 55368 


ANALYTICAL   EXPERIMENTS.  819 

The  solution  of  magnesia  prepared  in  the  cold  way  has  a  feeble  yet  distinct 
alkaline  reaction,  which  is  most  easily  perceived  upon  the  addition  of  very 
faintly  reddened  tincture  of  Jitmus;  the  alkaline  reaction  of  the  solution  is 
perfectly  manifest  also  with  slightly  reddened  litmus  paper,  or  with  turmeric 
or  dahlia  paper,  if  these  test-papers  are  left  for  some  time  in  contact  with  the 
solution. 

Alkali  carbonates  fail  to  render  the  solution  turbid,  even  upon  boiling. 

Sodium  phosphate  also  fails  to  impair  the  clearness  of  the  solution,  but  if 
the  fluid  is  mixed  with  a  little  ammonia  and  shaken,  it  speedily  becomes  turbid, 
and  deposits  after  some  time  a  perceptible  precipitate  of  ammonium  magnesium 
phosphate. 

b.  In  Hot  Water. 

Upon  boiling  pure  magnesia  with  water,  a  solution  is  obtained  which  com- 
ports itself  in  every  respect  like  the  cold-prepared  solution  of  magnesia.  A 
hot-prepared  solution  of  magnesia  does  not  become  turbid  upon  cooling,  nor 
does  a  cold-prepared  solution  upon  boiling.  84*82  grm.  of  hot-prepared  solution 
of  magnesia  left  0'0016  grm.  MgO. 

38.  SOLUBILITY  OP  PURE  MAGNESIA  IN  SOLUTIONS  OF  POTASSIUM  CHLORIDE 
AND  SODIUM  CHLORIDE  (to  §  74,  d). 

3  flasks  of  equal  size  were  charged  as  follows : — 

1.  With  1  grm.  pure  potassium  chloride,  200  c.c.  water  and  some  perfectly 
pure  magnesia. 

2.  With  1  grm.  pure  sodium  chloride,  200  c.c.  water  and  some  pure  magnesia. 

3.  With  200  c.c.  water  and  some  pure  magnesia. 

The  contents  of  the  3  flasks  were  kept  boiling  for  40  minutes,  then  filtered, 
and  the  clear  filtrates  mixed  with  equal  quantities  of  a  mixture  of  sodium 
phosphate,  ammonium  chloride  and  ammonia.  After  12  hours  a  very  slight 
precipitation  was  visible  in  3,  and  a  considerably  larger  precipitation  had  taken 
place  in  1  and  2. 

39.  PRECIPITATION  OP  ALUMINIUM  BY  AMMONIA.  ETC.  (to  §  75,  a). 

a.  Ammonia  produces  in  neutral  solutions  of  aluminium  salts  or  of  alum,  as 
is  well  known,  a  gelatinous  precipitate  of  aluminium  hydroxide.    Upon  further 
addition  of  ammonia  in  considerable  excess,  the  precipitate  redissolves  gradually, 
but  not  completely. 

b.  If  a  drop  of  a  dilute  solution  of  alum  is  added  to  a  copious  amount  of 
ammonia,  and  the  mixture  shaken,  the  solution  appears  almost  perfectly  clear; 
however,  after  standing  at  rest  for  some  time,  slight  flakes  separate. 

c.  If  a  solution  of  aluminium,  mixed  with  a  large  amount  of  ammonia,  is 
filtered,  and 

«.  The  filtrate  boiled  for  a  considerable  time,  flakes  of  aluminium  hydroxide 
separate  gradually  in  proportion  as  the  excess  of  ammonia  escapes. 

ft.  The  filtrate  mixed  with  solution  of  ammonium  chloride,  a  very  percep- 
tible flocculent  precipitate  of  aluminium  hydroxide  separates  immediately;  the 
whole  of  the  aluminium  present  in  the  solution  will  thus  separate  if  the 
ammonium  chloride  be  added  in  sufficient  quantity. 

y.  The  filtrate  mixed  with  ammonium  sesquicarbonate,  the  same  reaction 
takes  place  as  in  ft. 


820  ANALYTICAL    EXPERIMENTS. 

8.  The  filtrate  mixed  with  solution  of  sodium  chloride  or  of  potassium 
,  chloride,  no   precipitate   separates,    but,    after   several  days'   standing,    slight 
flakes   of  aluminium  hydroxide   subside,  owing   to   the  loss  of  ammonia  by 
evaporation. 

d.  If  a  neutral  solution  of  aluminium  is  precipitated  with  ammonium  car 
bonate,  or  if  a  solution  strongly  acidified  with  hydrochloric  or  nitric  acid  is 
precipitated  with  pure  ammonia,  or  if  to  a  neutral  solution  a  sufficient  amount 
of  ammonium  chloride  is  added  besides  the  ammonia;  even  a  considerable 
excess  of  the  precipitants  will  fail  to  redissolve  the  precipitated  aluminium 
hydroxide,  as  appears  from  the  continued  perfect  clearness  of  the  filtrates  upon 
protracted  boiling  and  evaporation. 

40.  PRECIPITATION  OP  ALUMINIUM  BY  AMMONIUM  SULPHIDE  (to  §  75,  a). 
(Experiments  made  by  Mr.  J.  FUCHS,  formerly  Assistant  in  my  Laboratory.) 

a.  50  c.c.  of  a  solution  of  pure  ammonium-alum,  which  contained  0'3939 
A12O3,  were  mixed  with  50  c.c.   water  and  10  c.c.  solution  of  ammonium 
sulphide,  and  filtered  after  ten   minutes.     The  ignited  precipitate  weighed 
0-3825  grm. 

b.  The  same  experiment  was  repeated  with  100  c.c.  water;  the  precipitate 
weighed  0-3759  grm. 

c.  The  same  experimeut  was  repeated  with  200  c.c.  water;  the  precipitate 
weighed  0*3642  grm. 

41.  PRECIPITATION  OF  CHROMIUM  BY  AMMONIA  (to  §  76,  a). 

Solutions  of  chromic  chloride  and  of  chrome-alum  (concentrated  and  dilute, 
neutral  and  acidified  with  hydrochloric  acid)  were  mixed  with  ammonia  in 
excess.  All  the  filtrates  drawn  off  immediately  after  precipitation  appeared 
red,  but  when  filtered  after  ebullition,  they  all  appeared  colorless,  if  the  ebullition 
had  been  sufficiently  protracted. 

42.  SOLUBILITY  OF  THE  BASIC  ZINC  CARBONATE  IN  WATER  (to  §  77,  a). 
Perfect^  pure,  recently  (hot)  precipitated  basic  zinc  carbonate  was  gently 

'heated  with  distilled  water,  and  subsequently  digested  cold  for  many  weeks, 
with  frequent  shaking.  The  clear  solution  gave  no  precipitate  with  ammonium 
sulphide,  not  even  after  long  standing. 

84-82  grm.  left  0'0014  grm.  zinc  oxide,  which  corresponds  to  0'0019  basic 
zinc  carbonate  (74  per  cent,  of  ZnO  being  assumed  in  this  salt).  One  part  of 
the  basic  carbonate  requires  therefore  44642  parts  of  water  for  solution. 

IN  EACH   OF   THE   THREE    FOLLOWING  NUMBERS  THE  SULPHIDE  WAS  PRECIPI- 

tated  from  the  solution  of  the  normal  salt  with  addition  of  ammonium  chloride 
by  yellow  ammonium  sulphide,  and  allowed  to  stand  in  a  closed  vessel.  After 
24  hours  the  clear  fluid  was  poured  on  to  6  filters  of  equal  size,  and  the 
precipitate  was  then  equally  distributed  among  them.  The  washing  was  at 
once  commenced  and  continued,  without  interruption,  the  following  fluids 
being  used: — 

I.  Pure  water. 
II.  Water  containing  hydrogen  sulphide. 

III.  Water  containing  ammonium  sulphide. 

IV.  Water  containing  ammonium  chloride,  afterwards  pure  water. 


ANALYTICAL   EXPERIMENTS.  821 

V.  Water  containing  hydrogen  sulphide  and  ammonium  chloride,  after- 
wards water  containing  hydrogen  sulphide. 

VI.  Water  containing  ammonium  sulphide  and  ammonium  chloride,  after- 
wards water  containing  ammonium  sulphide. 

43.  DEPORTMENT  OF  ZINC  SULPHIDE  ON  WASHING  (to  §  77,  c). 

The  filtrates  were  at  first  colorless  and  clear.  On  washing,  the  first  three 
filtrates  ran  through  turbid,  the  turbidity  was  strongest  in  II.  and  weakest  in 
III. ;  the  last  three  remained  quite  clear.  On  adding  ammonium  sulphide  no 
change  took  place;  the  turbidity  of  the  first  three  was  not  increased,  the  clearness 
of  the  last  three  was  not  impaired.  Ammonium  chloride  therefore  decidedly 
exercises  a  favorable  action,  and  the  water  containing  it  may  be  displaced  by 
water  containing  ammonium  sulphide. 

44.  DEPORTMENT  OP  MANGANESE  SULPHIDE  ON  WASHING  (to  §  78,  e). 
The  filtrates  were  at  first  clear  and  colorless.     But  after  the  washing  had 

been  continued  some  time,  I.  appeared  colorless,  slightly  opalescent;  II.  whitish 
and  turbid;  III.  yellowish  and  turbid;  IV.  colorless,  slightly  turbid;  V.  slightly 
yellowish,  nearly  clear;  VI.  clear,  yellowish.  To  obtain  a  filtrate  that  remains 
clear,  therefore,  the  wash-water  must  at  first  contain  ammonium  chloride. 
Addition  of  ammonium  sulphide  also  cannot  be  dispensed  with,  as  all  the 
filtrates  obtained  without  this  addition  gave  distinct  precipitates  of  manganese 
sulphide  when  the  reagent  was  subsequently  added  to  them. 

45.  DEPORTMENT  OP  NICKEL  SULPHIDE  (ALSO  OP  COBALT  SULPHIDE  AND 
FERROUS  SULPHIDE)  ON  WASHING  (to  §  79,  e). 

In  the  experiments  with  nickel  sulphide  the  clear  filtrates  were  put  aside, 
and  then  the  washing  was  proceeded  with.  The  washings  of  the  first  3  ran 
through  turbid,  of  the  last  three  clear.  When  the  washing  was  finished,  I.  was 
colorless  and  clear;  II.  blackish  and  clear;  III.  dirty  yellow  and  clear;  IV. 
colorless  and  clear;  V.  slightly  opalescent;  VI.  slightly  brownish  and  opal- 
escent. On  addition  of  ammonium  sulphide,  I.  became  brown;  II.  remained 
unaltered;  III.  remained  unaltered;  IV.  became  black  and  opaque;  V.  became 
brown  and  clear;  VI.  became  pure  yellow  and  clear. 

Cobalt  sulphide  and  ferrous  sulphide  behaved  in  an  exactly  similar  manner. 
It  is  plain  that  these  sulphides  oxidize  more  rapidly  when  the  wash-water  con- 
tains ammonium  chloride,  unless  ammonium  sulphide  is  also  present.  Hence 
it  is  necessary  to  wash  with  a  fluid  containing  ammonium  sulphide;  and  the 
addition  of  ammonium  chloride  at  first  is  much  to  be  recommended,  as  this 
diminishes  the  likelihood  of  our  obtaining  a  muddy  filtrate. 

46.  DEPORTMENT  OP  COBALTOUS  HYDROXIDE  PRECIPITATED  BY  ALKALIES 

(to  §  80,  a}. 

A.  solution  of  cobaltous  chloride  was  precipitated  boiling  with  solution  of 
soda,  and  the  precipitate  washed  with  boiling  water  until  the  filtrate  gave  no 
longer  the  least  indication  of  presence  of  chlorine.  The  dried  and  ignited 
residue,  heated  with  water,  manifested  no  alkaline  reaction.  It  was  reduced  by 
ignition  in  hydrogen  gas,  and  the  metallic  cobalt  digested  hot  with  water.  The 
decanted  water  manifested  no  alkaline  reaction,  even  after  considerable  con- 
centration ;  but  the  metallic  cobalt,  brought  into  contact,  moist,  with  turmeric 
paper,  imparted  to  the  latter  a  strong  brown  color. 


'822  ANALYTICAL   EXPERIMENTS. 

47.  SOLUBILITY  OF  LEAD  CARBONATE  (to  §  83,  a). 
a.  In  pure  Water. 

'  Recently  precipitated  and  thoroughly  washed  pure  lead  carbonate  was 
digested  for  8  days  with  water  at  the  common  temperature,  with  frequent 
shaking.  84 '42  grm.  of  the  filtrate  were  evaporated,  with  addition  of  some 
pure  sulphuric  acid;  the  residuary  lead  sulphate  weighed  0'0019  grm.,  which 
corresponds  to  0 '00167  lead  carbonate.  One  part  of  the  latter  salt  dissolves 
therefore  in  50551  parts  of  water.  The  solution,  mixed  with  hydrogen  sulphide 
water,  remained  perfectly  colorless,  not  the  least  tint  being  detected  in  it,  even 
upon  looking  through  it  from  the  top  of  the  test-cylinder. 

b.  In  Water  containing  a  little  Ammonium  Acetate  and   also  Ammonium 

Carbonate  and  Ammonia. 

A  highly  dilute  solution  of  pure  lead  acetate  was  mixed  with  ammonium 
carbonate  and  ammonia  in  excess,  and  the  mixture  gently  heated  and  then 
allowed  to  stand  at  rest  for  several  days.  84'42  grm.  of  the  filtrate  left,  upon 
evaporation  with  a  little  sulphuric  acid,  0'0041  grm.  lead  sulphate,  which 
corresponds  to  0'0036  of  the  carbonate.  One  part  of  the  latter  salt  requires 
accordingly  23450  parts  of  the  above  fluid  for  solution.  The  solution  was 
mixed  with  hydrogen  sulphide  water;  when  looking  through  the  fluid  from  the 
top  of  the  test-cylinder,  a  distinct  coloration  was  visible;  but  when  looking 
through  the  cylinder  laterally,  this  coloration  was  hardly  perceptible.  Traces 
of  lead  sulphide  separated  after  the  lapse  of  some  time. 

c.  In  Water  containing  a  large  propoi'tion  of  Ammonium  Nitrate,  together 

with  Ammonium  Carbonate  and  Caustic  Ammonia. 

A  highly  dilute  solution  of  lead  acetate  was  mixed  with  nitric  acid,  then 
with  ammonium  carbonate  and  ammonia  in  excess;  the  mixture  was  gently 
heated,  and  allowed  to  stand  at  rest  for  8  days.  The  filtrate,  mixed  with 
hydrogen  sulphide,  exhibited  a  very  distinct  brownish  color  upon  looking 
through  it  from  the  top  of  the  cylinder;  but  this  color  appeared  very  slight 
only  when  looking  through  the  cylinder  laterally.  The  amount  of  lead  dissolved 
was  unquestionably  more  considerable  than  in  b. 

48.  SOLUBILITY  OF  LEAD  OXALATE  (to  §  83,  b). 

A  dilute  solution  of  lead  acetate  was  precipitated  with  ammonium  oxalate 
and  ammonia,  the  mixture  allowed  to  stand  at  rest  for  some  time,  and  then 
filtered.  The  filtrate,  mixed  with  hydrogen  sulphide,  comported  itself  exactly 
like  the  filtrate  of  No.  47,  b.  The  same  deportment  was  observed  in  another 
similar  experiment,  in  which  ammonium  nitrate  had  been  added  to  the  solution. 

49.  SOLUBILITY  OF  LEAD  SULPHATE  IN  PURE  WATER  (to  §  83,  d). 

Thoroughly  washed  and  still  moist  lead  sulphate  was  digested  for  5  days 
with  water,  at  10 — 15°,  with  frequent  shaking.  84 '42  grm.  of  the  filtrate  (filtered 
off  at  11°)  left  0-0037  grm.  lead  sulphate.  Consequently  1  part  of  this  salt 
requires  22816  parts  of  pure  water  of  11°  for  solution. 

The  solution,  mixed  with  hydrogen  sulphide,  exhibited  a  distinct  brown 
color  when  viewed  from  the  top  of  the  cylinder,  but  this  color  appeared  very 
slight  upon  looking  through  the  cylinder  laterally. 


ANALYTICAL   EXPERIMENTS.  823 

50.  SOLUBILITY  OF  LEAD  SULPHATE  IN  WATER  CONTAINING  SULPHURIC 
Acm  (to  §  83,  d). 

A  highly  dilute  solution  of  lead  acetate  was  mixed  with  an  excess  of  dilute 
pure  sulphuric  acid;  the  mixture  was  very  gently  heated,  and  the  precipitate 
allowed  several  days  to  subside.  80 '31  grm.  of  the  filtrate  left  0'0022  grm.  lead 
sulphate.  One  part  of  this  salt  dissolves  therefore  in  36504  parts  of  water  con- . 
taining  sulphuric  acid.  The  solution,  mixed  with  hydrogen  sulphide,  appeared 
colorless  to  the  eye  looking  through  the  cylinder  laterally,  and  very  little  darker 
when  viewed  from  the  top  of  the  cylinder. 

51.  SOLUBILITY  OF  LEAD  SULPHATE  IN  WATER  CONTAINING  AMMONIUM 
SALTS  AND  FREE  SULPHURIC  ACID  (to  §  83,  d ). 

A  highly  dilute  solution  of  lead  acetate  was  mixed  with  a  tolerably  large 
amount  of  ammonium  nitrate,  and  sulphuric  acid  in  excess  added.  After 
several  days'  standing,  the  mixture  was  filtered.  The  filtrate  was  nearly 
indifferent  to  hydrogen  sulphide  water;  viewed  from  the  top  of  the  cylinder,  it 
looked  hardly  perceptibly  darker  than  pure  water. 

52.  DEPORTMENT  OF  LEAD  SULPHATE  UPON  IGNITION  (to  §  83,  d). 

Speaking  of  the  determination  of  the  atomic  weight  of  sulphur,  ERDMANN 
and  MARCHAND*  state  that  lead  sulphate  loses  some  sulphuric  acid  upon 
ignition.  In  order  to  inform  myself  of  the  extent  of  this  loss,  and  to  ascertain 
how  far  it  might  impair  the  accuracy  of  the  method  of  determining  lead  as  a 
sulphate,  I  heated  2 '2151  grm.  of  absolutely  pure  PbSo*  to  the  most  intense 
redness,  over  a  spirit-lamp  with  double  draught,  I  could  not  perceive  the 
slightest  decrease  of  weight;  at  all  events,  the  loss  did  not  amount  to  0 '0001  grm. 

53.  DEPORTMENT  OF  LEAD  SULPHIDE  ON  DRYING  AT  100°  (to  §  83,  /). 

Lead  sulphide  was  precipitated  from  a  solution  of  pure  lead  acetate  with 
hydrogen  sulphide,  and  when  dry,  kept  for  a  considerable  time  at  100°  and 
weighed  occasionally.  The  following  numbers  represent  the  results  of  the 
several  weighings : — 

I.  0-8154.        II.  0-8164.        III.  0'8313.        IV.  0'8460.        V.  0'864 

54.  DEPORTMENT  OF  METALLIC  MERCURY  AT  THE  COMMON  TEMPERATURE 
AND  UPON  EBULLITION  WITH  WATER  (to  §  84,  a). 

To  ascertain  in  what  manner  loss  of  metallic  mercury  occurs  upon  drying, 
and  likewise  upon  boiling  with  water,  and  to  determine  which  is  the  best 
method  of  drying,  I  made  the  following  experiments: — 

I  treated  6'4418  grm.  of  perfectly  pure  mercury  in  a  watch-glass,  with  dis- 
tilled water,  removed  the  water  again  as  far  as  practicable  (by  decantation  and 
finally  by  means  of  blotting-paper),  and  weighed.  I  now  had  6 '4412  grm.  After 
several  hours'  exposure  to  the  air,  the  mercury  was  reduced  to  6 '4411.  I  placed 
these  6-4411  grm.  under  a  bell- jar  over  sulphuric  acid,  the  temperature  being 
about  17°.  After  the  lapse  of  24  hours  the  weight  had  not  altered  in  the  least. 
I  introduced  the  6*4411  grm.  mercury  into  a  flask,  treated  it  with  a  copious 
quantity  of  distilled  water,  and  boiled  for  15  minutes  violently.  I  then  placed 
the  mercury  again  upon  the  watch-glass,  dried  it  most  carefully  with  blotting  - 


*  Journ.  fur  Prakt.  Chem.  31,  385. 


824  ANALYTICAL   EXPERIMENTS. 

paper,  and  weighed.  The  weight  was  now  6 '4402  grm.  Finding  that  a  trace 
of  mercury  had  adhered  to  the  paper,  I  repeated  the  same  experiment  with  the 
6*4402  grin.  After  15  minutes'  boiling  with  water,  the  mercury  had  again  lost 
0'0004  grm.  The  remaining  6'4398grm.  were  exposed  to  the  air  for  6  days  (in 
summer,  during  very  hot  weather),  after  which  they  were  found  to  have  lost 
only  0-0005  grm. 

55.  DEPORTMENT  OF  MERCURIC  SULPHIDE  WITH  SOLUTION  OF  POTASSA, 
AMMONIUM  SULPHIDE,  ETC.  (to  §  84,  c). 

a.  If  recently  precipitated  pure  mercuric  sulphide  is  boiled  with  pure  solu- 
tion of  potassa,  not  a  trace  of  it  dissolves  in  that  fluid;   hydrochloric  acid 
produces  no  precipitate,  nor  even  the  least  coloration,  in  the  filtrate. 

b.  If  mercuric  sulphide  is  boiled  with  solution  of  potassa,  with  addition  of 
some  hydrogen   sulphide  water,   ammonium  sulphide,    or   sulphur,   complete 
solution  is  effected. 

c.  If  freshly  precipitated  mercuric  sulphide  is  digested   in  the   cold  with 
yellowish  or  very  yellow  ammonium  sulphide,  slight  but  distinctly  perceptible 
traces  are  dissolved,  while  in  the  case  of  hot  digestion  scarcely  any  traces  of 
mercury  can  be  detected  in  the  solution.* 

d.  Thoroughly  washed  mercuric  sulphide,  moistened  with  water,  suffers  no 
alteration  upon  exposure  to  the  air ;  at  least,  the  fluid  which  I  obtained  by 
washing  mercuric  sulphide  which  had  been  thus  exposed  for  24  hours,  did  not 
manifest  acid  reaction,  nor  did  it  contain  mercury  or  sulphuric  acid. 

56.  DEPORTMENT  OF  CUPRIC  OXIDE  UPON  IGNITION  (to  §  85,  b). 

Pure  cupric  oxide  (prepared  from  cupric  nitrate)  was  ignited  in  a  platinum 
crucible,  then  cooled  under  a  bell-jar  over  sulphuric  acid,  and  finally  weighed. 
The  weight  was  3 '542  grm.  The  oxide  was  then  most  intensely  ignited  for 
5  minutes,  over  a  BERZELIUS'  lamp,  and  weighed  as  before,  when  the  weight 
was  found  unaltered;  the  oxide  was  then  once  more  ignited  for  5  minutes,  but 
with  the  same  result. 

57.  DEPORTMENT  OF  CUPRIC  OXIDE  IN  THE  AIR  (to  §  85,  b}. 

A  platinum  crucible  containing  4*3921  grm.  of  gently  ignited  cupric  oxide 
(prepared  from  the  nitrate)  stood  for  10  minutes,  covered  with  the  lid,  in  a 
warm  room  (in  winter);  the  weight  of  the  oxide  was  found  to  have  increased  to 
4-3939  grm. 

The  oxide  was  then  intensely  ignited  over  a  spirit-lamp ;  after  10  minutes' 
standing  in  the  covered  crucible,  the  weight  had  not  perceptibly  increased  r 
after  24  hours'  it  had  increased  by  0*0036  grm.  N 

58.  DEPORTMENT  OF  BISMUTH  SULPHIDE  UPON  DRYING  AT  100°  (to  §  86,  g).. 

0  4558  grm.  of  bismuth  sulphide  prepared  in  the  wet  wTay  were  placed  in 
the  desiccator  on  a  watch-glass,  and  allowed  to  stand  at  the  common  tempera- 
ture. After  3  hours  the  weight  was  0'4270,  after  6  hours  0*4258,  after  2  days- 
the  same. 

0*3602  grm.  of  the  bismuth  sulphide  so  dried  was  put  into  a  water-bath,  in 
15  minutes  it  weighed  0*3596,  half  an  hour  afterwards  0'3599,  in  half  an  hour 


*  Comp.  my  experiments  in  the  Zeitschrift  f.  Anal.  Chem.  3,  140. 


ANALYTICAL   EXPERIMENTS.  825 

more  0-3603,  in  two  hours  0'3626.     In  a  second  experiment  the  drying  was  kept 
up  for  4  days,  and  a  continual  increase  of  weight  was  observed. 

0-5081  grm.  of  bismuth  sulphide  dried  in  the  desiccator  was  heated  in  a 
boat  iii  a  stream  of  carbonic  acid.  After  gentle  ignition  the  weight  was  0'5002, 
after  repeated  heating  0'4992.  The  bismuth  sulphide  was  visibly  volatilized  on 
ignition  in  the  current  of  carbonic  acid. 

59.  DEPORTMENT  OF  CADMIUM  SULPHIDE  WITH  AMMONIA,  ETC.  (to  §  87,  c). 

Recently  precipitated  pure  cadmium  sulphide  was  diffused  through  water, 
and  the  following  experiments  were  made  with  the  mixture : 

a.  A  portion  was'digested  cold  with  ammonia  in  excess,  and  filtered.     The 
nitrate  remained  perfectly  clear  upon  addition  of  hydrochloric  acid. 

b.  Another  portion  was  digested  hot  with  excess  of  ammonia,  and  filtered. 
This  filtrate  likewise  remained  perfectly  clear  upon  addition  of  hydrochloric 
acid. 

c.  Another  portion  was  digested  for  some  time  with  solution  of  potassium 
cyanide,  and  filtered.     This  filtrate  also  remained  perfectly  clear  upon  addition 
of  hydrochloric  acid. 

d.  Another    portion    was    digested  with    ammonium    hydrosulphide,    and 
filtered.     The  turbidity  which  hydrochloric  acid  imparted  to  this  filtrate  was 
pure  white. 

(A  remark  made  by  WACKENRODER,  in  BUCHNER'S  Repertor.  d.  Pharm., 
xlvi.  226,  induced  me  to  make  these  experiments.) 

60.  DEPORTMENT  OF  PRECIPITATED  ANTIMONIOUS  SULPHIDE  ON  DRYING 

(to  §  90,  a). 

0-2899  grm.  of  pure  precipitated  antimonious  sulphide  dried  in  the  desiccator 
lost,  when  dried  at  100°,  O'OOOT. 

0*4457  grm.  of  the  substance  dried  at  100°  lost,  when  heated  to  blackening 
in  a  stream  of  carbonic  acid,  0*0011  water. 

0-1932  grm.  of  the  substance  dried  at  100°  gave  up  0*0012,  when  heated  to 
blackening  in  a  stream  of  carbonic  acid,  and  after  stronger  heating,  during 
which  fumes  of  antimony  sulphide  began  to  escape,  the  total  loss  amounted  to 
0-0022  grm. 

0-1670  grm.  of  the  substance  dried  at  100°  lost  O'OOOS  grm.  on  being  heated 
to  blackening  in  a  stream  of  carbonic  acid. 

61.  AMOUNT  OF  WATER  IN  HYDRATED  SILICA  (to  §  93,  9). 

(Experiments  made  by  my  assistant,  Mr.  LIPPERT.) 

A  dilute  solution  of  soluble  glass  was  slowly  dropped  into  hydrochloric  acid, 
as  long  as  the  precipitate  continued  to  dissolve  rapidly,  then  the  clear  fluid  was 
heated  in  the  water-bath,  till  it  set  to  a  transparent  jelly.  This  jelly  was  dried 
as  far  as  possible  with  blotting  paper,  diffused  in  water,  and  washed  by  decan- 
tation  till  the  fluid  altogether  ceased  to  give  the  chlorine  reaction.  It  was  then 
transferred  to  a  filter,  and  the  latter  spread  on  blotting  paper  and  exposed  till  a 
crumbly  mass  was  left  from  the  spontaneous  evaporation  of  water.  One  half 
(I.)  was  dried  for  8  weeks  in  the  desiccator  over  sulphuric  acid,  with  occasional 
trituration,  the  other  half  (II.)  was  dried  under  similar  circumstances,  but  in 
a  vacuum.  Both  were  transferred  to  closed  tubes  and  these  were  kept  in  the 
desiccator. 


826  ANALYTICAL    EXPERIMENTS. 

The  weighing  of  the  substance  dried  at  100°  was  effected  between  watch 
glasses.  For  the  purpose  of  igniting  the  residue,  it  was  allowed  to  satiate  itself 
with  aqueous  vapor  by  exposure  to  the  air,  otherwise  a  considerable  quantity  of 
the  substance  would  have  been  lost,  then  water  was  dropped  upon  it  in  the 
watch-glass,  then  it  was  rinsed  into  a  platinum  crucible,  dried  in  a  water-bath, 
and  ignited,  at  first  cautiously,  towards  the  end  intensely. 

The  substance  I.  contained                                           Expt.  i.  Expt.  2. 

Water,  escaping  at  or  below  100° 4*19  ^  q.no 

above  100° 4*76  i 

Silica..                                                                        .  91-05  90-72 


100-00         100-00 

Consequently  the  hydrate  dried  at  100°  consists  of  4'97  water  and  95 -03  silica. 
In  the  substance  dried  in  the  desiccator  the  oxygen  of  the  total  water :  the 
oxygen  of  the  silica  (SiO2),  according  to  the  first  experiment  :  :  1  :  6*1,  according 
to  the  second  experiment  :  :  1  :  5  "86.  And  in  the  substance  dried  at  100°  the 
oxygen  of  the  water  :  the  oxygen  of  the  silica  :  :  1  :  11 '5. 

The  substance  II.  contained                       Expt.  1.  Expt.  2.       Expt.  3. 

Water,  escaping  at  or  below  100° 4'75  4'71 

above  100° 5*26  5  "21 

Silica..                                                   .    89-99  90'08          90'05 


100-00        100-00         100-00 

Consequently  the  hydrate  dried  at  100°  consists  on  the  average  of  5 '49  water 
and  94*51  silica.  In  the  substance  dried  in  a  vacuum  over  sulphuric  acid  the 
oxygen  of  the  total  water  :  the  oxygen  of  the  silica — on  an  average  :  :  1  :  5'41. 
And  in  the  substance  dried  at  100°  the  oxygen  of  the  water  :  the  oxygen  of  the 
.silica  :  :  1  :  10 '43. 

62.  DETERMINATION  OF  BARIUM  BY  PRECIPITATION  WITH  AMMONIUM  CAR- 
BONATE (to  §  101,  2,  a). 

0*7553  grm.  pure  ignited  barium  chloride  precipitated  after  §101,  2,  a,  gave 
0-7142  BaCO3,  which  corresponds  to  0'554719  BaO  =  73'44  per  cent.  (100  parts 
•of  BaCl2  ought  to  have  given  73'59  parts).  The  result  accordingly  was  99 '79 
instead  of  100. 

63.  DETERMINATION  OP  BARIUM  IN  ORGANIC  SALTS  (to  §  101,  2,  ft). 

0'686  grm.  barium  racemate,  treated  according  to  §  101,  2,  b,  gave  0*408 
barium  carbonate  -  0'3169  BaO  =  46'20  per  cent,  (calculated  46*38  percent.); 
i.e.,  99*61  instead  of  100. 

64.  DETERMINATION  OF  STRONTIUM  AS  STRONTIUM   SULPHATE  (to  §  102, 
1,  a). 

a.  An  aqueous  solution  of  1-2398  grm.  SrCl2  was  precipitated  with  sulphuric 
acid  in  excess,  and  the  precipitated  strontium  sulphate  washed  with  water.     It 
weighed  1-4113,  which  corresponds  to  0'795408  SrO  =  64*15  per  cent,  (calculated 
•65-38  per  cent.);  i.e.,  98'12  instead  of  100. 

b.  1  -1510  grm.  SrCo3  was  dissolved  in  excess  of  hydrochloric  acid,  the  sola- 


ANALYTICAL    KXPKRI.M  KNTS.  827 

tion  diluted,  and  then  precipitated  with  sulphuric  acid;  the  precipitated  SrSO4 
was  washed  with  water;  it  weighed  1*4024  =  0*79039  SrO  =  68'68  per  cent, 
(calculated  70 '07  per  cent.);  i.e.,  98.02  instead  of  100. 

65.  DETERMINATION  OF  STRONTIUM  AS  SULPHATE,  WITH  CORRECTION  (to 
£  102,  1,  a). 

^hQ  filtrate  obtained  hi  No.  64,  b,  weighed  190*84  grm.  According  to  experi- 
ment No.  22,  11862  parts  of  water  containing  sulphuric  acid  dissolve  1  part  of 
strontium  sulphate;  therefore,  190*84  grm.'  dissolve  0*0161.  The  washing* 
weighed  63 '61  grm.  According  to  experiment  No.  21,  6895  parts  of  water 
dissolve  1  part  of  SrSO«;  therefore,  63*61  grm.  dissolve  0*0092  grm. 

Adding  0*0161  and  0-0092  to  the  1*4024  actually  obtained,  we  find  the  total 
amount  =  1*4277  grm.,  which  corresponds  to  0*80465  SrO  =  69*91  per  cent,  in 
SrCO3  (calculated  70 '07  per  cent.);  i.e.,  99*77  instead  of  100. 

66.  DETERMINATION  OF  STRONTIUM  AS  STRONTIUM  CARBONATE  (to  §  102,  2). 

1*3104  grm.  strontium  chloride,  precipitated  according  to  §  102,  2,  gave 
1*2204  SrCO3,  containing  0  8551831  SrO  =  65*26  per  cent,  (calculated  65*38); 
i.e.,  99*82  instead  of  100. 

IN   THE   FOUR    FOLLOWING   EXPERIMENTS,    AND   ALSO   IN   No.    72,    PURE   AIR- 

dried  calcium  carbonate  was  used,  in  a  portion  of  which  the  amount  of  anhydrous 
carbonate  had  been  determined  by  very  cautious  heating.  0*7647  grm.  left 
0*7581  grm.,  which  weight  remained  unaltered  upon  further  (extremely  gentle) 
ignition;  the  air-dried  carbonate  contained  accordingly  55 '516  per  cent,  of  lime. 

67.  DETERMINATION  OF  CALCIUM  AS  CALCIUM  SULPHATE  BY  PRECIPITATION 
(to  g  103,  1,  a). 

1*186  grin,  of  "the  air  dried  calcium  carbonate"  was  dissolved  in  hydro- 
chloric acid,  and  the  solution  precipitated  with  sulphuric  acid  and  alcohol,  after 
§  103,  1,  a.  Obtained  1*5949  grm.  CaSO4,  containing  0*65598  CaO,  i.e.,  55*31 
per  cent,  (calculated  55*51),  which  gives  99*64  instead  of  100. 

68.  DETERMINATION    OF    CALCIUM    AS    CaCO3,  BY  PRECIPITATION    WITH 
AMMONIUM  CARBONATE  AND  WASHING  WITH  PURE  WATER  (to  §  103,  2,  a). 

A  hydrochloric  acid  solution  of  1*1437  grm.  of  "the  air-dried  calcium  car- 
bonate" gave  upon  precipitation  as  directed,  1*1243  grin,  anhydrous  calcium 
carbonate,  corresponding  to  0*629608  CaO  =  55*05  per  cent,  (calculated  55  "51 
per  cent.),  which  gives  99*17  instead  of  100. 

69.  DETERMINATION  OF  CALCIUM  AS  CaCO3,  BY  PRECIPITATION  WITH  AMMO- 
NIUM OXALATE  FROM  ALKALINE  SOLUTION  (to  §  103,  2,  b.  a). 

1*1734  grm.  of  "the  air-dried  calcium  carbonate"  dissolved  in  hydrochloric 
acid,  and  treated  as  directed  §103,  2,  b,  a,  gave  1*1632  grm.  CaCO3  (reaction 
not  alkaline),  containing  0*651392  of  CaO  =  55*513  per  cent,  (calculated  55*516 
per  cent.),  which  gives  99*99  instead  of  100. 

70.  DETERMINATION  OF  CALCIUM  AS  OXALATE  (to  §  103,  2,  b,  a). 

0*857  grm.  of  "the  air-dried  calcium  carbonate"  were  dissolved  in  hydro- 
chloric acid;  the  solution  was  precipitated  with  ammonium  oxalate  and 


828  ANALYTICAL   EXPERIMENTS. 

ammonia,  the  precipitate  washed,  and  then  dried  at  100°,  until  the  weight 
remained  constant,  The  precipitate  (CaC2O4  +  H2O)  weighed  1*2461  grm.  con- 
taining G'477879  CaO  —  55*76  per  cent,  (calculated  55'516  per  cent.),  which  gives 
100-45  instead  of  100. 

71.  VOLUMETRIC  DETERMINATION  OF  CALCIUM  PRECIPITATED  AS  OXALATE 
(to  §  103,  2,  b,  a). 

Six  portions,  of  10  c.c.  each,  were  taken  of  a  solution  of  pure  calcium 
chloride ;  in  2  portions  the  calcium  was  determined  in  the  gravimetric  way  (by 
precipitation  with  ammonium  oxalate,  and  weighing  CaCO3) ;  in  two  by  the 
alkalimetric  method  (p.  236),  and  in  two  by  precipitation  with  ammonium 
oxalate,  and  estimation  of  the  oxalic  acid  in  the  precipitate  by  solution  of  potas- 
sium permanganate.  The  following  were  the  results  obtained : 

a.  In  the  gravimetric  b   By  the  alkalimetric        c.  By  solution  of  potas- 

way.  method.  sium  permanganate. 

0*5617  CaCO3  0'5614  0'5613 

0-5620      "  0-5620  0'5620 

72.  DETERMINATION  OF  CALCIUM  AS  CaCO3  BY  PRECIPITATION  AS  CALCIUM 
OXALATE  FROM  ACID  SOLUTION  (to  §  103,  2,  b,  fi). 

0*857  grm.  of  "the  air-dried  calcium  carbonate"  dissolved  in  hydrochloric 
acid  and  precipitated  from  this  solution  according  to  the  directions  of  §  103,  2, 
b,  ft,  gave  0'8476  calcium  carbonate  (which  did  not  manifest  alkaline  reaction, 
and  the  weight  of  which  did  not  vary  in  the  least  upon  evaporation  with 
ammonium  carbonate),  containing  0-474656  CaO  =  55 -39  per  cent,  (calculated 
55-51),  which  gives  99 '78  instead  of  100. 

73.  DETERMINATION  OF  MAGNESIUM  AS  Mg2P2O7  (to  §  104,  2). 

a.  A  solution  of  1  -0587  grm.  pure  anhydrous  magnesium  sulphate  in  water, 
precipitated  according  to  §  104,  2,  gave  0*9834  magnesium  pyrophosphate,  con- 
taining 0-35438  MgO  =  33*476  per  cent,  (calculated  33'33  per  cent.),  which  gives 
100 -43  instead  of  100. 

b.  0*9672  MgSO4  gave  0*8974  Mg2P2O7  =  33*43  per  cent,  of  MgO  (calculated 
33*33,  which  gives  100-30  instead  of  100. 

74.  PRECIPITATION  OF  ZINC  ACETATE  BY  HYDROGEN  SULPHIDE  (to  §  108,  b). 

a.  A  soluble  of  pure  zinc  acetate  was  treated  with  the  gas  in  excess,  allowed 
to  stand  at  rest  for  some  time,  and  then  filtered.     The  filtrate  was  mixed  with 
ammonia.     It  remained  perfectly  clear  at  first,  and  even  after  long  standing  a 
few  hardly  visible  flakes  only  had  separated. 

b.  A  solution  of  zinc  acetate  to  which  a  tolerably  large  amount  of  acetic  acid 
had  been  added  previously  to  the  precipitation  with  hydrogen  sulphide,  showed 
exactly  the  same  deportment. 

75.  DETERMINATION  OF  IRON  AS  SULPHIDE  (to  §  113,  2). 

10  c.c.  of  a  pure  solution  of  ferric  chloride  was  precipitated  with  ammonia; 
obtained  0*1453  Fe2O3  =  0-10171  Fe. 

10  c.c.  was  precipitated  with  ammonia  and  ammonium  sulphide,  and  treated 
after  §  113,  2,  obtained  0*1596  FeS  —  0*10157  Fe. 

10  c.c.  again  yielded  0.1605  FeS  =  0*1021  Fe. 


ANALYTICAL   EXPERIMENTS.  829 

76.  DETERMINATION  OF  LEAD  AS  CHROMATE  (to  §  116,  4). 

1  '0083  grm.  pure  lead  nitrate  were  treated  according  to  §  116,  4.  The  pre- 
cipitate was  collected  on  a  weighed  filter,  and  dried  at  100°,  obtained  0'9871 
grm.  =  0-67833  PbO.  This  gives  67  3  per  cent.  Calculation  67 '4. 

0 '9814  lead  nitrate  again  yielded  0'9625  chromate  =  67.4  per  cent. 

77.  DETERMINATION  OF  MERCURY  IN  THE  METALLIC  STATE,  IN  THE  WET 
WAY,  BY  MEANS  OF  STANNOUS  CHLORIDE  (to  §  118,  1,  b). 

2*01  grm.  mercuric  chloride  gave  1*465  gnu.  metallic  mercury  =  72 '88  per 
cent,  (calculated  73 '83  per  cent.),  which  gives  98 "71  instead  of  100  (&CHAFFNER). 
The  loss  is  not  inherent  in  the  method,  i.e.,  it  does  not  arise  from  mercury 
evaporating  during  the  ebullition  and  desiccation  (Expt.  No.  54);  but  its  origin 
lies  in  the  fact  that  one  usually  does  not  allow  sufficient  time  for  the  mercury  to 
settle  quite  completely,  and  in  general  is  not  careful  enough  in  decanting,  and 
drying  with  paper,  &c. 

78.  DETERMINATION  OF  COPPER  BY  PRECIPITATION  WITH  ZINC  IN  A  PLA- 
TINUM DISH  (to  §  119,  2). 

30'882  grm.  pure  cupric  sulphate  were  dissolved  in  water  to  250  c.c.;  10  c.c. 
of  the  solution  contained  accordingly  0 '31387  grm.  metallic  copper. 

a.  10  c.c.  precipitated  with  zinc  in  a  platinum  dish,  gave  0"3140  =  100 '06 
per  cent. 

b.  In  a  second  experiment  10  c.c.  gave  0*3138  =  100  per  cent. 

80.  DETERMINATION  OF  COPPER  AS  CUPROUS  SULPHOCYANATE  (to  §  119, 
3,  b). 

0'5965  grm.  of  pure  cupric  sulphate  was  dissolved  in  a  little  water,  and,  after 
addition  of  an  excess  of  sulphurous  acid,  precipitated  with  potassium  sulphocy- 
anate.  The  well  washed  precipitate,  dried  at  100°,  weighed  0'2893,  correspond- 
ing to  0-1892  CuO  =31*72  percent.  As  cupric  sulphate  contains  31 '83  per 
cent.,  this  gives  99'66  instead  of  100. 

81.  DETERMINATION  OF  COPPER  BY  DE  HAEN'S  METHOD  (to  §  119,  4,  a). 

Four  10  c.c. -s  of  a  solution  of  cupric  sulphate,  each  10  c.c.,  containing  0"0254 
grm.  Cu,  were  severally  mixed  with  potassium  iodide,  then  with  50  c.c.  of  a 
solution  of  sulphurous  acid  (50  c.c.  corresponding  to  12*94  c.c.  iodine  solution). 
After  addition  of  starch  paste,  iodine  solution  was  added  until  the  fluid 
appeared  blue. 

This  required, — 

In  a,  4-09 

b,  3-95 

c,  4-06 

d,  3-95 

As  100  c.c.  of  iodine  solution  contained  0-58043  grrn.  iodine,  this  gives — 
For  a,  0-0256  Cu  instead  of  0'0254 

"    b,  0-0260 

"    c,  0-0257 

"    d,  0-0260 
Another  experiment,  made  with  100  c.c.  of  the  same  solution  of  cupric  sul- 


830  ANALYTICAL   EXPERIMENTS. 

phate,  gave  0'2606  instead  of  0*254  of  copper.  Ammonium  nitrate  having  been 
added  to  10  c.c.  of  the  solution  of  cupric  sulphate,  then  some  dilute  hydro- 
chloric acid,  3*4  and  3*5  c.c.  of  iodine  solution  were  required  instead  of  4  c.c. — 
a  proof  that  considerably  more  iodine  had  separated  than  corresponded  to  the 
copper. 

83.  PRECIPITATION  OF  BISMUTH  NITRATE  BY  AMMONIUM  CARBONATE  (to 
§  120,  1,  a). 

If  a  solution  of  bismuth  nitrate,  no  matter  whether  containing  much  or  little 
free  nitric  acid,  is  mixed  with  water,  precipitated  with  ammonium  carbonate 
and  ammonia,  and  filtered  without  applying  heat,  the  filtrate  acquires,  upon 
addition  of  hydrogen  sulphide  water,  a  blackish-brown  color.  But  if  the 
mixture  before  filtering  is  heated  for  a  short  time  nearly  to  boiling,  hydrogen 
sulphide  fails  to  impart  this  color  to  the  filtrate,  or,  at  all  events,  the  change  of 
color  is  hardly  visible  to  the  eye  looking  through  the  full  test-tube  from  the  top. 

84.  DETERMINATION  OP  ANTIMONY  AS  SULPHIDE  (to  §  125,  1). 

0*559  grm.  of  pure  air-dried  tartar  emetic,  treated  according  to  §  125, 1,  gave 
0'2902  grm.  antimonious  sulphide  dried  at  100°  =  '2492  grm.  or  44*58  per  cent, 
of  antimonious  oxide.  Heated  to  blackening  in  a  current  of  carbonic  acid,  the 
precipitate  lost  0"0079  grm.  (reckoned  from  a  part  to  the  whole),  leaving  accord- 
ingly 0'2823  grm.  of  anhydrous  antimonious  sulphide,  which  corresponds  to 
0*24245  grm.,  or  43'37  per  cent,  of  antimonious  oxide.  As  the  tartar  emetic 
contains  43 '70  per  cent,  of  antimonious  oxide,  the  process  gives,  if  the  precipitate 
is  dried  at  100°,  102*01;  if  heated  to  blackening,  99*22  instead  of  100. 

89.  DETERMINATION  OF  PHOSPHORIC  ACID  AS  MAGNESIUM  PYROPHOSPHATE 
(to  §  134,   b,   a). 

1-9159  and  2.0860  grm.  pure  crystallized  sodium  hydrogen  phosphate,  treated 
as  directed  §  134,  b,  a,  gave  0'5941  and  0*6494  grm.  of  magnesium  pyrophos- 
phate  respectively.  These  give  19 '83  and  19'91  per  cent,  of  P2O5  in  sodium 
hydrogen  phosphate,  instead  of  19*83  per  cent. 

90.  DETERMINATION   OF  PHOSPHORIC  ACID  AS  URANYL  PYROPHOSPHATK 
(to  §  134,  c). 

30  c.c.  of  a  solution  of  pure  sodium  hydrogen  phosphate,  treated  with 
magnesium  sulphate,  ammonium  chloride,  and  ammonia,  as  directed  §  134,  b,  a, 
gave  0*3269  grm.  of  magnesium  pyrophosphate.  10  c.c.  contained  accordingly 
0-06982  grm.  of  phosphoric  anhydride. 

10  c.c.  of  the  same  solution  were  then  precipitated  with  uranyl  acetate  as 
directed  §  134,  c.  The  ignited  precipitate  was  treated  with  a  little  nitric  acid, 
then  again  ignited  ;  after  cooling,  it  weighed  0*3478  grm.  corresponding  to 
0-06954  grm.  of  phosphoric  anhydride. 

91.  DETERMINATION  OF  FREE  HYDROGEN  SULPHIDE  BY  MEANS  OF  SOLU- 
TION OF  IODINE  (to  §  148,  I.,  a). 

The  experiments  were  made  to  settle  the  following  questions: — 


ANALYTICAL    EXPERIMENTS.  831 

«.  Does  the  quantity  of  iodine  required  remain  the  same  for  solutions  of 
hydrogen  sulphide  of  different  degrees  of  dilution? 

b.  Does  the  equation  H2S  + 12  =  2HS  -f  S  really  represent  the  decomposition 
which  takes  place? 

The  hydrogen  sulphide  water  was  contained  in  a  flask  closed  by  a  doubly- 
perforated  cork ;  into  one  aperture  a  siphon  with  pinchcock  was  fitted,  to  draw 
off  the  fluid;  into  the  other  aperture  a  short  open  tube,  which  did  not  dip  into 
the  fluid. 

Question  a. 

a.  About  30  c.c.  of  iodine  solution  were  introduced  into  a  flask,  which  was 
then  tared ;  hydrogen  sulphide  water  was  added  until  the  yellow  color  had  just 
disappeared.  The  flask  was  then  closed,  weighed,  starch  paste  added,  and  then 
solution  of  iodine  until  the  fluid  appeared  blue. 

70'2  grm.  H2S  water  required  23'4  c.c.  iodine  solution,  100  accordingly 
33-33  c.c. 

68 '4  grm.  required  22 '7  c.c.  iodine  solution,  100  accordingly  33 '20  c.c. 
ft.  Same  process;  but  the  fluid  was  diluted  with  water  free  from  air. 

61 '5  grm.  H2S  water -f- 200  grm.  water  required  20"7  c.c.  iodine  solution, 
100  accordingly  33 '65  c.c. 

52 '4  grm.  -j-  400  grm.  water  required  17.7  c.c.  iodine  solution,  100  accord- 
ingly 33-77. 

The  iodine  solution  contained  0 '00498  iodine  in  1  c.c.  Considering  that 
addition  of  a  larger  volume  of  water  necessarily  involves  a  slight  increase  in 
the  quantity  of  iodine  solution,  these  results  may  be  considered  sufficiently 
corresponding. 

Question  b. 

According  to  a,  100  grm.  of  the  H2S  water  contained  0-02215  grm.  H2S, 
assuming  the  proportion  to  be  100  :  33'2. 

173  "6  grm.  of  the  same  water  were,  immediately  after  the  experiments  in  a, 
drawn  off  into  a  hydrochloric  acid  solution  of  arsenious  acid;  after  24  hours,  the 
arsenious  sulphide  was  filtered  off,  dried  at  100°,   and  weighed.     0"0920  grm. 
were  obtained,  which  corresponds  to  0 '03814  H2S,  or  a  percentage  of  0 '02197. 
The  second  question  also  is  therefore  answered  in  the  affirmative. 

92.  SOLUTION  OF  MAGNESIUM  CHLORIDE  DISSOLVES  CALCIUM:  OXALATE  (to 
S  154,  6). 

If  some  calcium  chloride  is  added  to  a  solution  of  magnesium  chloride,  then 
a  little  ammonium  oxalate,  no  precipitate  is  formed  at  first ;  but  upon  slightly 
increasing  the  quantity  of  ammonium  oxalate,  a  trifling  precipitate  gradually 
separates  after  some  time. 

If  an  excess  of  ammonium  oxalate  is  added,  the  whole  of  the  calcium  is 
thrown  down,  but  the  precipitate  contains  also  magnesium  oxalate.  This  shows 
that  to  effect  the  separation  of  the  two  bases  by  ammonium  oxalate,  the  reagent 
must  be  added  in  excess;  whilst,  on  the  other  hand,  in  the  presence  of  much 
magnesium,  the  operator  must  expect  to  precipitate  some  of  the  magnesium,  as 
the  following  experiments  (No.  93)  clearly  show. 

93.  SEPARATION  OP  CALCIUM  FROM  MAGNESIUM  (to  §  154,  6). 

The  fluids  employed  in  the  following  experiments  were,  a  solution  of  calcium 


832  ANALYTICAL   EXPERIMENTS. 

chloride,  10  c.c.  of  which  corresponded  to  0 '5618  CaCO3;  a  solution  of  magne- 
sium chloride,  containing  0*250  MgO  in  10  c.c. ;  a  solution  of  ammonium 
chloride  (1  :  8);  solution  of  ammonia,  containing  10  per  cent.  NH3;  solution  of 
ammonium  oxalate  (1  :  24);  acetic  acid,  containing  30  per  cent.  C2H4O2. 

The  precipitation  was  effected  at  the  common  temperature;  the  precipitate 
of  calcium  oxalate  was  filtered  off  after  20  hours. 

a.  Influence  of  the  degree  of  dilution. 

a.  10  c.  c.  MgCl2,  10  c.  c.  CaCl2,  10  c.  c.  NH4C1,  4  drops  JSTH4OH,  50 
c.c.  water,  20  c.  c.  (NH4)2C2O4.  Result,  0'5705  CaCO3. 

ft.  Same  as  a,  with  150  c.c,  water  instead  of  50  c.c.  Eesult,  0'5670 
CaCO3. 

b.  Influence  of  excess  of  ammonia. 

Same  as  a,  ft  + 10  c.c.  NH4OH.     Result,  0*5614  grin.  CaCO3. 

c.  Influence  of  excess  of  ammonium  chloride. 

Same  as  a,  ft  +  40  c.c.  NH4C1.     Result,  0*5652  grm. 

d.  Influence  of  excess  of  ammonia  and  ammonium  chloride. 

Same  as  a,  ft  +  30  c.c.  NH4C1  -f 10  c.c.  NH4OH.     Result,  0*5613  grm. 

e.  Influence  of  free  acetic  acid. 

Same  as  a,  ft,  only  with  6  drops  C2H4O2,  instead  of  the  4  drops  NH4OH. 
Result,  0-5594  grm. 

/.  Influence  of  excess  of  ammonium  oxalate  in  feebly  alkaline  solution. 
Same  as  a,  /?  +  20  c.c.  (NH4)2C2O4.     Result,  0'5644  grm.  CaCO3^ 
g.  Influence  of  excess  of  ammonium  oxalate  in  strongly  alkaline  solution. 

Same  as  a,  ft,  +  10  c.c.  NH4OH  +  20  c.c.  (NH4)2C2O4.  Result, 
0-5644. 

7i.  Influence  of  excess  of  ammonium  oxalate  in  presence  of  much  NH4C1  and 
NH4OH. 

Same  as  a,  ft,  -f  10  NH.OH  +  30  NH4C1  +  20  (NH4)aC9O4.  Result, 
0-5709  grm. 

i.  Influence  of  excess  of  ammonium  oxalate  in  solution  slightly  acidified 
with  C2H4O2. 

Same  as  a,  ft,  -  4  drops  NH4OH  +  6  drops  C3H4O2  -f  20  c.c.  (NH4)2 
C2O4.  Result,  0-5661  grm. 

Consequently,  when  a  notable  amount  of  magnesium  is  present  there  is 
always  a  chance  of  magnesium  oxalate,  or  ammonium  magnesium  oxalate  pre- 
cipitating along  with  the  calcium  oxalate. 

Another  series  of  experiments  in  which  a  solution  of  magnesium  oxalate  in 
hydrochloric  acid  was  mixed  with  ammonia  under  varying  circumstances,  proved 
also  that,  in  presence  of  a  notable  quantity  of  magnesium,  magnesium  oxalate, 
or  magnesium  ammonium  oxalate,  will  always  separate  after  standing  for  some 
time,  no  matter  whether  in  a  cold  or  a  warm  place. 

In  a  third  series  of  experiments,  the  separation  was  effected  by  double  pre- 
cipitation, in  accordance  with  §154,  28.  The  same  solutions  were  employed  as 
in  the  first  series,  with  the  exception  of  the  magnesium  chloride,  for  which  a 
solution  was  substituted  containing  0*2182  grm.  MgO,  in  10  c.c. 

10  c.c.  CaCl2  -f  30  c.c.  MgCl2  +  20  c.c.  NH4C1,  +  300  c.c.  water,  +  6  drops 
ammonia,  +  a  sufficient  excess  of  ammonium  oxalate.  Results,  in  two  experi- 
ments, 0-5621  and  0'5652,  mean  0-5636,  instead  of  0'5618  CaCO3;  also  0'6660 
and  0-6489  MgO,  mean  0'6574,  instead  of  0'6546. 


ANALYTICAL   EXPERIMENTS.  833 

94.  SEPARATION  OF  IODINE  FKOM  CHLORINE  BY  PISANI'S  METHOD. 

0-2338  grm.  potassium  iodide,  dissolved  in  water,  -f-  \  c.c.  of  solution  of 
iodide  of  starch,  required  14  c.c.  of  decinormal  silver  solution  =  0 '2322  grm. 
potassium  iodide. 

G'3025  grm.  potassium  iodide,  mixed  with  about  double  the  quantity  of 
sodium  chloride,  required  18 '2  c.c.  silver  solution  =  0'3021  KI. 

0-2266  grm.  potassium  iodide,  mixed  with  about  100  times  as  much  sodium 
chloride,  required  13 '7  c.c.  silver  solution  =  0'2272  KI. 

95.  SEPARATION  OF  IODINE  FROM  BROMINE,  BY  PISANI'S  METHOD. 

0*3198  grm.  potassium  iodide,  mixed  with  double  the  quantity  of  potassium 
bromide,  required  19 '2  c.c.  of  decinormal  silver  solution  =  0'3187  KI. 

99.  CHLORIMETRICAL  EXPERIMENTS  (to  §  199). 

10  grm.  of  chloride  of  lime  were  rubbed  up  with  water  to  one  litre,  with 
which  the  following  experiments  were  made : 

a.  By  PENOT'S  method  (§  200);  obtained  23 '5  and  23*5  per  cent. 

b.  By  means  of  iron  (§  201,  modification);  obtained  23'6  per  cent 

c.  By  BUNSEN'S  method  (§  201);  results,  23*6— 23 '6  per  cent. 

100.  DRYING  OF  MANGANESE  (to  §  202,  I.). 

Four  small  pans,  containing  each  8  grm.  of  manganese  of  53  per  cent.,  were 
first  heated  in  the  water-bath.  After  3  hours,  I.  had  lost  0145;  after  6  hours, 
II.  0-15;  after  9  hours,  III.  015;  after  12  hours,  IV.  015  grm.  I.  and  II. 
having  been  left  standing,  loosely  covered,  in  the  room  for  12  hours,  II.  was 
found  to  weigh  exactly  as  much  as  at  first;  I.  wanted  only  O'Ol  grm.  of  the 
original  weight. 

The  four  pans  were  now  heated  for  2  hours  to  120°.  .  After  cooling,  they 
were  found  to  have  lost  each  0180  of  the  original  weight.  I.  and  II.  having  been 
left  standing,  loosely  covered,  in  the  room  for  60  hours,  were  found  to  have  again 
acquired  their  original  weight  by  attracting  moisture.  III.  and  IV.  were  heated 
for  2  hours  to  150°.  The  loss  of  weight  in  both  cases  was  0'215  grm.  Having 
been  left  standing,  loosely  covered,  in  the  room  for  72  hours,  both  were  found 
to  weigh  0*05  less  than  at  first.  Assuming  the  hygroscopic  moisture  expelled  to 
be  reabsorbed  by  standing  in  the  air,  this  shows  that  at  150°  a  little  chemically 
combined  water  escapes  along  with  the  moisture,  and  accordingly  that  the  tem- 
perature must  not  exceed  120°. 

My  experiments  will  be  found  described  in  detail  in  DINGLER'S  polyt.  Journ., 
135,  277  et  seq. 


834  CALCULATION    OF   ANALYSIS. 


CALCULATION  OF  ANALYSES. 

THE  calculation  of  the  results  obtained  by  an  analysis  presupposes,  as  an  in- 
dispensable preliminary,  a  knowledge  of  the  general  laws  of  the  combining 
proportions  of  bodies,  on  the  one  hand,  and  of  the  more  simple  rules  of  arith- 
metic on  the  other.  It  is  a  great  error  to  suppose  that  the  ability  to  make 
chemical  calculations  involves  an  extensive  acquaintance  with  mathematics,  a 
knowledge  of  decimal  fractions  and  simple  equations  being  for  the  most  part 
sufficient.  These  remarks  are  not  intended  to  dissuade  students*  of  chemistry 
from  pursuing  the  highly  important  study  of  mathematics;  but  merely  to 
encourage  those  who  have  had  no  opportunity  of  entering  more  deeply  into  this 
science,  and  who,  as  experience  has  shown  me,  are  often  afraid  to  venture  upon 
chemical  calculations.  For  this  reason,  I  have  made  the  whole  of  the  calculations 
given  in  the  following  paragraphs,  in  the  most  intelligible  manner  possible,  and 
without  logarithms. 

I.  Calculation  of  the  Constituents  sought  from  the  Compound  obtained  in  ihe 
Analytical  Process,  and  exhibition  of  the  Result  in  Per-cents. 

The  bodies  the  weight  of  which  it  is  intended  to  determine,  are  separated,  as 
we  have  seen  in  Division  I.,  treating  of  the  "  Execution  of  Analysis,"  either  in 
the  free  state,  or — and  this  most  frequently — in  combinations  of  known  com- 
position. The  results  are  usually  calculated  upon  100  parts  of  the  examined 
substance,  since  this  gives  a  clearer  and  more  intelligible  view  of  the  composi- 
tion. In  cases  where  the  several  constituents  have  been  separated  in  the  free 
state,  the  calculation  may  be  made  at  once ;  but  if  the  constituents  have  been 
separated  in  combination  with  other  substances,  they  must  first  be  calculated 
from  the  compounds  obtained. 

1.  Calculation  of  the  Results  into  Per-cents  by  Weight,  in  Cases  where  the 
Substance  sought  has  been  separated  in  the  Free  State. 

a.  Solid  Bodies,  Liquids,  and  Gases,  which  have  been  determined  by  Weight. 

The  calculation  here  is  exceedingly  simple. 

Suppose  you  have  analyzed  mercurous  chloride,  and  separated  the  mercury 
in  the  metallic  state.  2'945  grm.  mercurous  chloride  have  given  say  2'499  grm, 
metallic  mercury. 

2-945  :  2-499  ::  100  :  x 

x  =  84-85, 

which  means  that  your  analysis  shows  100  parts  of  mercurous  chloride  to  con- 
tain 84-85  of  mercury,  and  consequently  15*15  of  chlorine. 

Now  as  mercurous  chloride  is  known  to  consist  of  2  at.  mercury  and  2  at. 
chlorine,  and  as  the  atomic  weights,  of  both  these  elements  are  also  known,  the 
true  percentage  composition  of  the  body  may  be  readily  calculated  from  these 
data.  When  analyzing  substances  of  known  composition  for  practice,  the 
results  theoretically  calculated  and  those  obtained  by  the  analysis  are  usually 
placed  in  juxtaposition,  as  this  enables  the  student  at  once  to  perceive  the  degree 
of  accuracy  with  which  the  analysis  has  been  performed. 


CALCULATION    OF   ANALYSIS.  835 

Thus  for  instance — 

Found.                            Calculated  (compare  §  84,  &). 
Mercury 84'85 84'94 

Chlorine..  .  15'15  .  .  15'06 


100-00  100-00 

b.   Gases  ichich  have  been  determined  by  Measure. 

If  a  gas  has  been  determined  by  measure,  it  is,  of  course,  necessary  first  to 
ascertain  the  weight  corresponding  to  the  volume  found,  before  the  percentage 
by  weight  can  be  calculated. 

But  as  the  exact  weights  of  a  definite  volume  of  the  various  gases  have  been 
severally  determined  by  accurate  experiments,  this  calculation  also  is  a  simple 
rule-of-three  question,  if  the  gas  may  be  measured  under  the  same  circumstances 
to  which  the  known  relation  of  weight  to  volume  refers.  The  circumstances  to 
be  taken  into  consideration  here,  are: 

Temperature  and  Atmospheric  Pressure. 
Besides  these,  the 

Tension  of  the  Aqueous  Vapor 

may  also  claim  consideration  in  cases  where  water  is  used  as  the  confining  fluid, 
or  generally  where  the  gas  has  been  measured  in  the  moist  state, 

The  respective  weights  assigned  in  Table  V.*  to  1  litre  of  the  gases  there 
enumerated,  refer  to  a  temperature  of  0°,  and  an  atmospheric  pressure  of  0*76 
metre  of  mercury.  We  have,  therefore,  in  the  first  place,  to  consider  the  manner 
in  which  volumes  of  gas  measured  at  another  temperature  and  another  height 
of  the  barometer,  are  to  be  reduced  to  0°  and  0-76  of  the  barometer. 

a.  Reduction  of  a  Volume  of  Gas  of  any  given  Temperature  to  0°,  or  any  other 
Temperature  between  0°  and  100°. 

The  following  propositions  regarding  the  expansion  of  gases  were  formerly 
universally  adopted: 

1.  All  gases  expand  alike  for  an  equal  increase  of  temperature. 

The  expansion  of  one  and  the  same  gas  for  each  degree  of  the  thermometer 
is  independent  of  its  original  density. 

Although  the  correctness  of  these  propositions  has  not  been  fully  confirmed 
by  the  minute  investigations  of  MAGNUS  and  REGNAULT,  yet  they  may  be  safely 
followed  in  reductions  of  the  temperature  of  those  gases  which  are  most 
frequently  measured  in  the  course  of  analytical  processes,  as  the  coefficients  of 
expansion  of  these  gases  scarcely  differ  from  each  other,  and  as  there  is  never 
any  very  considerable  difference  in  the  atmospheric  pressure  under  which  the 
gases  are  severally  measured. 

The  investigations  just  alluded  to  have  given 

0-3665 

as  the  coefficient  of  the  expansion  of  gases  which  comes  nearest  to  the  truth ;  in 
other  words,  as  the  extent  to  which  gases  expand  when  heated  from  the  freezing 
to  the  boiling  point  of  water.  They  expand,  therefore,  for  every  degree  of  the 
centigrade  thermometer, 

0-3665 


100 


=  0-003665. 


*  See  Tables  at  the  end  of  the  volume. 


836  CALCULATION    OF   ANALYSIS. 

If  we  wish  to  ascertain  how  much  space  1  c.  c.  of  gas  at  0°  will  occupy  at 
10°,  we  find 

1  X  [1  -f  (10  X  0-003665)]  =  1  "03665. 

If  we  wish  to  ascertain  how  much  space  100  c.  c.  at  0°  will  occupy  at 
10°,  we  find 

100  X[l  +  (10X0  -003665)] 
=  100x1-03665-103-665. 

If  we  wish  to  know  how  much  space  1  c.  c.  at  10°  will  occupy  at  0°,  we  find 


1  +  (10X  0-003665) 
How  much  space  do  103*665  c.  c.  at  10°  occupy  at  0°? 
103-665 


1  _|_  (10  x  0-003665) 


=  100. 


The  general  rule  of  these  calculations  may  be  expressed  as  follows: 
To  calculate  the  volume  of  a  gas  from  a  lower  to  a  higher  temperature,  we 
have  in  the  first  place  to  find  the  expansion  for  the  volume  unit,  which  is  done 
by  adding  to  1  the  product  of  the  multiplication  of  the  thermometrical  difference 
by  0*003665;  and  then  to  multiply  this  by  the  number  of  volume  units  found  in 
the  analytical  process.  On  the  other  hand,  to  reduce  the  volume  of  a  gas  from 
a  higher  to  a  lower  temperature,  we  have  to  divide  the  number  of  volume  units 
found  in  the  analytical  process,  by  1  +  the  product  of  the  multiplication  of  the 
thermometrical  difference  by  0 '003665. 

ft.  Reduction  of  the  Volume  of  a  Gas  of  a  certain  given  Density  to  '76  Metre 
Barometric  Pressure,  or  any  other  given  Pressure. 

According  to  the  law  of  MARIOTTE,  the  volume  of  a  gas  is  inversely  as  the 
pressure  to  which  it  is  exposed;  in  accordance  with. this,  a  gas  occupies  the 
greater  space  the  less  the  pressure  upon  it,  and  the  less  space  the  greater  the 
pressure  upon  it. 

Thus,  supposing  a  gas  to  occupy  a  space  of  10  c.  c.  at  a  pressure  of  1  atmos- 
phere, it  will  occupy  1  c.  c.  at  a  pressure  of  10  atmospheres,  and  100  c.  c.  at  a 
pressure  of  T^  atmosphere. 

Nothing,  therefore,  can  be  more  easy  than  the  reduction  of  a  gas  of  a  certain 
given  tension  to  760  mm.  bar.  pressure,  or  any  other  given  pressure,  e.g.,  1000 
mm.,  which  is  frequently  used  in  the  analysis  of  gases. 

Supposing  a  gas  to  occupy  100  c.  c.  at  780  mm.  bar.,  how  much  space  will  it 
occupy  at  760  mm.  ? 

760  :  780  ::  100  :  x 
x  =  102  -63. 

How  much  space  will  100  c.  c.  at  750  mm.  bar.  occupy  at  760  mm.  ? 

760  :  750  ::  100  :  x 
x  =  98-68. 

How  much  space  will  150  c.  c.  at  760  mm.  bar.  occupy  at  1000  mm.? 

1000  :  760  ::  150  :  x 
a;  =  114. 


CALCULATION    OF   ANALYSIS. 


837 


y.  Reduction  of  the  Volume  of  a  Ga#  saturated  with  Aqueous  Vapor,  to  its  actual 
Volume  in  the  Dry  State. 

It  is  a  well-known  fact  that  water  has  a  tendency,  at  all  temperatures,  to 
assume  the  gaseous  state.  The  degree  of  this  tendency  (the  tension  of  the  aque- 
ous vapor) — which  is  dependent  solely  and  exclusively  upon  the  temperature, 
and  not  upon  the  circumstance  of  the  water  being  in  vacua  or  in  any  gaseous 
atmosphere — is  usually  expressed  by  the  height  of  a  column  of  mercury  counter- 
balancing it.  The  following  table  indicates  the  amount  of  tension  for  the 
various  temperatures  at  which  analyses  are  likely  to  be  made.* 

TABLE. 


Temperature 
(in  degrees  C.) 


Tension  of  the 

aqueous  vapor 

expressed  in 


Temperature 
(in  degrees  C.) 


Tension  of  the 

aqueous  vapor 

expressed  in 


millimetres. 

millimetres. 

0 

4-525 

21 

18-505 

1 

4-867 

22 

19-675 

2 

5-231 

23 

20-909 

3 

5-619 

24 

22-211 

4 

6-032 

25 

23-582 

5 

6-471 

26 

25-026 

6 

6-939 

27 

26-547 

7 

7-436 

28 

28-148 

8 

7-964 

29 

29-832 

9 

8-525 

30 

31-602 

10 

9-126 

31 

33-464 

11 

9-751 

32 

35-419 

12 

10-421 

33 

37-473 

13 

11-130 

34 

39-630 

14 

11-882 

35 

41-893 

15 

.   12-677 

36 

44-268 

16 

13-519 

37 

46-758 

17 

14-409 

38 

49-368 

18 

15-351 

39 

52-103 

19 

16-345 

40 

54-969 

20 

17-396 

Therefore,  if  a  gas  is  confined  over  water,  its  volume  is,  cateris  paiibus, 
always  greater  than  if  it  were  confined  over  mercury;  since  a  quantity  of  aque- 
ous vapor,  proportional  to  the  temperature  of  the  water,  mixes  with  the  gas,  and 
the  tension  of  this  partly  counterbalances  the  column  of  air  that  presses  upon  the 
gas,  and  to  that  extent  neutralizes  the  pressure.  To  ascertain  the  actual  pressure 
upon  the  gas,  we  must  therefore  subtract  from  the  apparent  pressure  so  much  as 
is  neutralized  by  the  tension  of  the  aqueous  vapor. 

Suppose  we  had  found  a  gas  to  measure  100  c.c.  at  759  mm.  bar.,  the  tempera- 
ture of  the  confining  water  being  15° ;  how  much  space  would  this  volume  of 
gas  occupy  in  the  dry  state  and  at  760  mm.  of  the  barometer? 

Our  table  gives  the  tension  of  aqueous  vapor  at  15°  =  12*677;  the  gas  is  con- 
sequently not  under  the  apparent  pressure  of  759  mm. ,  but  under  the  actual 
pressure  of  759  -  12 '677  =  746-323  mm. 


*  Compare  Magnus,  Pogg.  Annal.  61,  247. 


838  CALCULATION    OF  ANALYSIS. 

The  calculation  is  now  very  simple;  it  proceeds  in  the  manner  shown  in  /?; 
we  say, 

760  :  746-323  ::  100  :  x 

x  =  98-20. 

When  the  volume  of  a  gas  has  thus  been  adjusted  by  the  calculations  in  a 
and  ft,  or  y,  to  the  thermometrical  and  barometrical  conditions  to  which  the 
data  of  Table  V.  refer,  the  percentage  by  weight  may  now  be  readily  calculated 
by  substituting  the  weight  for  the  volume,  and  proceeding  by  simple  rule  of 
three. 

What  is  the  percentage  by  weight  of  nitrogen  in  an  analyzed  substance,  of 
which  0'5  grm.  have  yielded  30  c.  c.  of  dry  nitrogen  gas  at  0°,  and  760  mm. 
bar.? 

In  Table  V.  we  find  that  1  litre  (1000  c.  c.)  of  nitrogen  gas  at  0°,  and  760  mm. 
bar.,  weighs  1-25456  grm. 
We  say  accordingly : 

1000  :  1-25456  ::  30  :  x 
x  =  0-0376. 
And  then : 

0-5  :  0-0376  ::  100  :  x 
x  =  7-52. 

The  analyzed  substance  contains  consequently  7 '52  per  cent,  by  weight  of 
nitrogen. 

DR.  GIBBS'  method  of  finding  at  once  the  total  correction  for  temperature,  press- 
ure, and  moisture  in  absolute  determinations  of  nitrogen,  or  other  gases:  * 

"I  take  a  graduated  tube,  which  I  fill  with  mercury,  then  displace  about 
two-thirds  of  the  mercury  with  air,  and  invert  the  tube  into  a  cistern  of  mercury. 
Then  I  make  four  or  five  determinations  of  the  volume  of  the  included  (moist) 
air  in  the  usual  manner,  and  find  the  volume  of  the  air  at  0°  and  760  mm.  as  a 
mean  of  all  the  determinations.  This  tube  I  call  the  companion  tube,  and  it 
always  hangs  in  the  little  room  I  use  for  gas  analyses.  Suppose  the  volume  of 
(dry)  air  at  0°  and  760  mm.  is  132 '35  c.  c. 

"Now,  in  making  an  absolute  nitrogen  determination  I  collect  the  nitrogen 
moist  over  mercury  in  a  graduated  tube,  and  then  suspend  the  measuring  tube 
by  the  side  of  the  companion  tube.  I  then  by  a  cord  and  pulley  bring  the  level 
of  the  mercury  in  the  two  tubes  to  correspond  exactly,  and  then  read  off  the 
volume  of  air  in  the  companion  tube  and  the  volume  of  nitrogen  in  the  measur- 
ing tube.  I  ought  to  have  stated  that  the  two  tubes  hang  in  the  same  cistern  of 
mercury.  Suppose  the  volume  of  air  in  the  companion  tube  to  be  143  c.  c. ;  then 
the  total  correction  for  temperature,  pressure,  and  moisture  will  be  143  —  132*35 
=  10*65  c.c.  The  correction  for  the  nitrogen  will  then  be  found  by  rule  of 
three.  As  the  observed  volume  of  air  in  the  companion  tube  is  to  the  observed 
volume  of  nitrogen,  so  is  (in  this  case)  10 '65  to  the  required  correction.  In  this 
way,  when  the  volume  of  air  in  the  companion  tube  is  once  found,  no  further 
observations  of  temperature,  pressure,  or  height  of  mercury  above  the  mercury  in  the 
cistern  are  necessary.  The  companion  tube  lasts  for  an  indefinite  time.  I  have 
even  used  it  filled  with  water,  without  any  appreciable  change  in  some  weeks, 
but  I  prefer  mercury.  As  the  two  tubes  hang  side  by  side,  there  is  never  an 

*  Private  communication. 


CALCULATION   OF   ANALYSIS.  839 

appreciable  difference  of  temperature.  My  results  are  most  satisfactory.  Wil- 
liamson &  Russell  have,  as  you  know,  used  a  companion  tube  for  equating 
pressures,  but  not  for  finding  the  total  value  of  the  temperature  and  pressure 
correction  at  once ;  and  I  believe  that  my  process  is  wholly  new.  Certainly  it  is 
wonderfully  convenient,  and  saves  all  tables  and  labor  of  computation." 

2.  Calculation  of  the  Results  into  Per-cents  by  Weight,  in  Cases  where  the  Body 
sought  has  been  separated  in  Combination,  or  where  a  Compound  has  to  be  deter- 
mined from  one  of  its -Constituents. 

If  the  body  to  be  determined  has  not  been  weighed  or  measured  hi  its  own 
form,  but  in  some  other  form,  e.g.,  carbonic  acid  as  calcium  carbonate,  sulphur 
as  barium  sulphate,  ammonia  as  nitrogen,  chlorine  by  a  standard  solution  of 
Iodine,  &c.,  its  quantity  must  first  be  reckoned  from  that  of  the  compound  found 
before  the  calculation  described  in  1  can  be  made. 

This  may  be  accomplished  either  by  rule  of  three  or  by  some  abridged  method. 

Suppose  we  have  weighed  hydrogen  in  the  form  of  water,  and  have  found  1 
grm.  of  water;  how  much  hydrogen  does  this  contain? 

A  molecule  of  water  consists  of: 

Hydrogen 2  at.  =    2  pts. 

Oxygen 1  at.  =  16    " 

18   " 
We  say  accordingly: 

18  :  2  ::  1  :  x 
x  =  011111. 

Or,  expressed  in  general  terms: 

Water  X  011111  =  Hydrogen. 
EXAMPLE. — 

517  of  water;  how  much  hydrogen? 
517  X  0-11111  =  57-444 

The  following  equation  results  also  from  the  above  proportion: 

18          l_ 
2    :=    x 

18    =   1 

X 

I 

.'.     X        =     - 

Or,  expressed  in  general  terms, 

Water  divided  by  9  =  Hydrogen. 
EXAMPLE. — 

517  of  water,  how  much  hydrogen? 

f  =  57-444. 

In  this  manner  we  may  find  for  every  compound  constant  numbers  by  which 
to  multiply  or  divide  the  weight  of  the  compound,  in  order  to  find  the  weight  of 
the  constituent  sought  (comp.  Table  III.*). 

*  See  Tables  at  the  end  of  the  volume. 


840 


CALCULATION   OF   ANALYSIS. 


Thus,  for  instance,  the  nitrogen  contained  in  ammonium  platinic  chloride 
may  be  obtained  by  multiplying .  the  weight  of  the  latter  by  0*06296 ;  thus  the 
carbon  may  be  calculated  from  carbonic  acid  by  multiplying  the  weight  of  the 
latter  by  0'2727,  or  dividing  it  by  3 '666. 

These  numbers  are  by  no  means  so  simple,  convenient,  and  easy  to  remember 
as  in  the  case  of  hydrogen.  It  is  therefore  advisable,  in  the  case  of  carbonic 
acid,  for  instance,  to  fix  upon  another  general  expression,  viz., 


Carbonic  acid  X  3 
_____ 


=  Carbon  ; 


12  parts  in  44  (=  T3T)  in  carbonic  acid  being  carbon,  as  may  be  seen  from  the 
composition: 

C    12 

O2  32 

44 

The  object  in  view  may  also  be  attained  in  a  very  simple  manner,  by  refer- 
ence to  Table  IV.,*  which  gives  the  amount  of  the  constituent  sought  for  every 
number  of  the  compound  found,  from  1  to  9  ;  the  operator  need,  therefore, 
simply  add  the  several  values  together. 

As  regards  hydrogen,  for  instance,  we  find : 


TABLE. 


Found.)  Sought, 
water  j  hydrogen 

1 
O'lllll 

2 

0-22222 

3 
0-33333 

4 
0-44444 

5 
0-55555 

6 
0-66667 

0-77778 

8 
0-88889 

9 

i-ooooo 

From  this  table  it  is  seen  that  1  part  of  water  contains  0-11111  of  hydrogen, 
that  5  parts  of  water  contain  0 '55555  of  hydrogen;  9  parts,  1 '00000,  &c. 

Now  if  we  wish  to  know,  for  instance,  how  much  hydrogen  is  contained  in 
5'17  parts  of  water,  we  find  this  by  adding  the  values  for  5  parts,  for  ^  part, 
and  for  T^  parts,  thus : 

0-55555 

O'Olllll 

0-0077778 


0-5744388 
Why  the  numbers  are  to  be  placed  in  this  manner,  and  not  as  follows: 

0-55555 
0-11111 

0-77778 


1-44444 


is  self-evident,  since  arranging  them  in  the  latter  way  would  be  adding  the  value 
for  5,  for  1,  and  for  7  (5  -f  1  -f  7  =  13),  and  not  for  5'17.     This  reflection  shows 


*  See  Tables  at  the  end  of  the  volume. 


CALCULATION   OF    ANALYSIS.  841 

also  that,  to  find  the  amount  of  hydrogen  contained  in  517  parts  of  water,  the 
points  must  be  transposed  as  follows : 

55-555 

1-1111 
0-77778 


57-44388 

3.  Calculation  of  the  Results  of  Indirect  Analyses  into  Per -cents  by  Weight. 

The  import  of  th?,  term  "  indirect  analysis"  as  defined  in  §  151,  p.  478  shows 
sufficiently  that  no  universally  applicable  rules  can  be  laid  down  for  the  calcula- 
tions which  have  to  be  made  in  indirect  analyses.  The  selection  of  the  right 
way  must  be  left  in  every  special  case  to  the  intelligence  of  the  analyst.  I  will 
here  give  the  mode  of  calculating  the  results  in  the  more  important  indirect 
separations  described  in  Section  V.  They  may  serve  as  examples  for  other 
similar  calculations. 

a.  Indirect  Determination  of  Sodium  and  Potassium. 

This  is  effected  by  determining  the  sum  total  of  the  chlorides,  and  the  chlo- 
rine contained  in  them. 

The  calculation  may  be  made  as  follows: 

Suppose  we  have  found  3  grm.  of  sodium  and  potassium  chlorides,  and  in 
these  3  grm.  1*6877  of  chlorine. 

At.  Chlorine.  Mol.  KC1.  Chlorine  found. 

35-46  :  74-59  ::  1-6877     :    x 

x  —  3-55007. 

If  all  the  chlorine  present  were  combined  with  potassium,  the  weight  of  the 
chloride  would  amount  to  3-55007.  As  the  chloride  weighs  less,  sodium  chloride 
is  present,  and  this  in  a  quantity  proportional  to  the  difference  (i.e.,  3 '55007  —  3 
=  -55007),  which  is  calculated  as  follows: 

The  difference  between  the  mol.  weight  of  KC1  and  that  of  NaCl  (16 -09)  is 
to  the  mol.  weight  of  NaCl  (58'50),  as  the  difference  found  is  to  the  sodium 
chloride  present : 

16-09  :  58-50  ::  '55007  :  x 

x  =   2  NaCl 
and  3  -  2  =   1  KC1. 

From  this  the  following  short  rule  is  derived: 

Multiply  the  quantity  of  chlorine  in  the  mixture  by  2 '1035,  deduct  from  the 
product  the  sum  of  the  chlorides,  and  multiply  the  remainder  by  3 '6358;  the 
product  expresses  the  quantity  of  sodium  chloride  contained  in  the  mixed  chlo- 
ride. 

b.  Indirect  Determination  of  Strontium  and  Calcium. 

This  may  be  effected  by  determining  the  sum  total  of  the  carbonates,  and  the 
carbonic  acid  contained  in  them  (§  154,  31).  Suppose  we  have  found  2  giro,  of 
mixed  carbonate,  and  in  these  2  grm.  0'7383  of  carbonic  acid. 

Mol.  C02  Mol.  SrCO3  CO2  found. 

44  14750  ::  0'7383     :    x 

x  =  2-47498. 


842  CALCULATION    OF   ANALYSIS. 

If,  therefore,  the  whole  of  the  carbonic  acid  were  combined  with  strontia, 
the  weight  of  the  carbonate  would  amount  to  2  '47498  grm.  The  deficiency, 
=  0-47498,  is  proportional  to  the  calcium  carbonate  present,  which  is  calculated 
as  follows: 

The  difference  between  the  molecule  of  SrCO3  and  the  molecule  of  CaCO3 
(47-50)  is  to  the  molecule  of  CaCO3  (100)  as  the  difference  found  is  to  the 
calcium  carbonate  contained  in  the  mixed  salt: 

,-.     47-5  :  100  ::  0  "47498  :  x 
x  =  1. 

The  mixture,  therefore,  consists  of  1  grm.  calcium  carbonate  and  1  grm. 
strontium  carbonate. 

From  this  the  following  short  rule  is  derived  : 

Multiply  the  carbonic  acid  found  by  3  '3523,  deduct  from  the  product  the  sum 
of  the  carbonates,  and  multiply  the  difference  by  2-10526;  the  product  expresses 
the  quantity  of  the  calcium  carbonate. 

c.  Indirect  Determination  of  Chlorine  and  Bromine  (§  169,  1). 

Let  us  suppose  the  mixture  of  silver  chloride  and  bromide  to  have  weighed 
2  grm.,  and  the  diminution  of  weight  consequent  upon  the  transmission  of 
chlorine  to  have  amounted  to  01  grm.  How  much  chlorine  is  there  in  the  mixed 
salt,,  and  how  much  bromine? 

The  decrease  of  weight  here  is  simply  the  difference  between  the  weight  of 
the  silver  bromide  originally  present,  and  that  of  the  silver  chloride  which  has 
replaced  it;  if  this  is  borne  in  mind,  it  is  easy  to  understand  the  calculation 
which  follows: 

The  difference  between  the  molecules  of  silver  bromide  and  silver  chloride  is 
to  the  molecule  of  silver  bromide  as  the  ascertained  decrease  of  weight  is  to  x, 
i.e.  ,  to  the  silver  bromide  originally  present  in  the  mixture  :  • 

44-49  :  187-88  ::  O'l  :  x 

x  =  0-422297. 

The  2  grm.  of  the  mixture  therefore  contained  0*422297  grm.  silver,  bromide, 
and  consequently  2  —  0-422297  —  1-577703  grm.  silver  chloride. 

It  results  from  the  above,  that  we  need  simply  multiply  the  ascertained 
decrease  of  weight  by 


to  find  the  amount  of  silver  bromide  originally  present  in  the  analyzed  mixture. 
And  if  we  know  this,  we  also  know  of  course  the  amount  of  the  silver  chloride; 
and  from  these  data  we  next  calculate  the  quantities  of  chlorine  and  bromine  in 
the  ordinary  way. 

SUPPLEMENT  TO  I. 

KEMARKS  ON  LOSS  AND   EXCESS  IN   ANALYSES,    AND  ON  TAKING  THE  AVERAGE. 

If,  in  the  analysis  of  a  substance,  one  of  the  constituents  is  estimated  from 
the  loss,  or,  in  other  words,  by  subtracting  from  the  original  weight  of  the  analyzed 
substance  the  ascertained  united  weight  of  the  other  constituents,  it  is  evident 
that  in  the  subsequent  percentage  calculation  the  sum  total  must  invariably  be 
100.  Every  loss  suffered  or  excess  obtained  in  the  determination  of  the  several 


CALCULATION    OF   ANALYSIS.  843 

constituents  will,  of  course,  fall  exclusively  upon  the  one  constituent  which  is 
estimated  from  the  loss.  Hence  estimations  of  this  kind  cannot  be  considered 
accurate,  unless  the  other  constituents  have  been  determined  by  good  methods, 
and  with  the  greatest  care.  The  accuracy  of  the  results  will,  of  course,  be  the 
greater,  the  less  the  number  of  constituents  determined  in  the  direct  way. 

If,  on  the  other  hand,  every  constituent  of  the  analyzed  compound  has  been 
determined  separately,  it  is  obvious  that,  were  the  results  absolutely  accurate, 
the  united  weight  of  the  several  constituents  must  be  exactly  equal  to  the  origi- 
nal weight  of  the  analyzed  substance.  Since,  however,  as  we  have  seen  in  §  96, 
certain  inaccuracies  attach  to  every  analysis,  without  exception,  the  sum  total  of 
the  results  in  the  percentage  calculation  will  sometimes  exceed,  and  sometimes 
fall  short  of,  100. 

In  all  cases  of  this  description,  the  only  proper  way  is  to  give  the  results  as 
actually  found. 

Thus,  for  instance,  PELOUZE  found,  in  his  analysis  of  chromate  of  potassium 
chloride, 

Potassium 21  -8& 

Chlorine 19'41 

Chromic  acid. .  58 '21 


99-50 
BERZELITJS,  in  his  analysis  of  potassium  uranate, 

Potassa 12'8 

Uranic  oxide 86 '8 

996 
PLATTNER,  in  his  analysis  of  pyrrhotite, 

Of  Fahlun.  Of  Brasil. 

Iron 59-72  59'64 

Sulphur 40-22  40'43 

99-94  100-07 

It  is  altogether  inadmissible  to  distribute  any  chance  deficiency  or  excess 
proportionately  among  the  several  constituents  of  the  analyzed  compound,  as 
such  deficiencj7  or  excess  of  course  never  arises  from  the  several  estimations  in 
the  same  measure;  moreover,  such  "doctoring"  of  the  analysis  deprives  other 
chemists  of  the  power  of  judging  of  its  accuracy.  No  one  need  be  ashamed  to 
confess  having  obtained  somewhat  too  little  or  somewhat  too  much  in  an  analysis, 
provided,  of  course,  the  deficiency  or  excess  be  confined  within  certain  limits, 
which  differ  in  different  analyses,  and  which  the  experienced  chemist  always 
knows  how  to  fix  properly. 

In  cases  where  an  analysis  has  been  made  twice,  or  several  times,  it  is  usual 
to  take  the  mean  as  the  most  correct  result.  It  is  obvious  that  an  average  of  the 
kind  deserves  the  greater  confidence  the  less  the  results  of  the  several  analyses 
differ.  The  results  of  the  several  analyses  must,  however,  also  be  given,  or,  at 
all  events,  the  maximum  and  minimum. 

Since  the  accuracy  of  an  analysis  is  not  dependent  upon  the  quantity  of  sub- 
stance employed  (provided  always  this  quantity  be  not  altogether  too  small),  the 
average  of  the  results  of  several  analyses  is  to  be  taken  quite  independently  of 
the  quantities  used ;  in  other  words,  you  must  not  add  together  the  quantities 
used,  on  the  one  hand,  and  the  weights  obtained  in  the  several  analyses  on  the 


844  CALCULATION    OF   ANALYSIS. 

other,  and  deduce  from  these  data  the  percentage  amount;  but  you  must  cal 
culate  the  latter  from  the  results  of  each  analysis  separately,  and  then  take  the 
mean  of  the  numbers  so  obtained. 

Suppose  a  substance,  which  we  will  call  AB,  contains  fifty  per  cent,  of  A; 
and  suppose  two  analyses  of  this  substance  have  given  the  following  results : 

(1)  2  grm.  AB  gave  0'99  grm.  of  A. 

(2)  50  "          "          24-00  " 

From  1,  it  results  that  AB  contains  49*50  per  cent,  of  A. 
"     2,  48-00 

Total 97-50 

Mean   ,, 48*75 

It  would  be  quite  erroneous  to  say 

2  -f  50  =  52  of  AB  gaye  0*99  +  24 '00  =  24-99  of  A, 
therefore  100  of  AB  contain  48 '06  of  A; 

for  it  will  be  readily  seen  that  this  way  of  calculating  destroys  nearly  altogether 
the  influence  of  the  more  accurate  analysis  (1)  upon  the  average,  on  account  of 
the  proportionally  small  amount  of  substance  used. 

II. -DEDUCTION  OF  FORMULAE. 

1.  From  the  percentages  of  single  elements  in  compounds. 

The  process  of  deducing  an  empirical  formula  from  the  expression  of  the 
composition  of  a  compound  in  parts  per  hundred  of  its  constituents  (i.e.,  its  per- 
centage composition)  will  be  readily  understood  by  considering  first  the  some- 
what simpler  reverse  process  of  calculating  percentage  compositions  from 
formulae. 

Applying  this  latter  process  to  the  formula,  for  instance,  of  mannite,  C6Hi4O6, 
we  first  compute  from  the  relative  number  of  atoms  of  the  elements  shown  by 
the  formula  the  relative  quantities  by  weight  of  each,  by  means  of  their  known 
atomic  weights. 

Carbon 6  at.  X  12  =    72  pts.  by  weight. 

Hydrogen..  14  "    X    1  =    14   "        " 
Oxygen 6  "   X  16  =    96   " 

182   "        "  of  mannite. 

Since  182  pts.  of  the  compound  contain  72  pts.  of  carbon,  the  number  of  pts. 
of  carbon  which  100  contain  may  be  found  by  the  rule  of  three: 

182  :  100  r  •  72  :  x 

^  X  72  =    39-56  carbon, 
lo-c 

100 
In  like  manner  — -  x  14  =     7-69  hydrogen. 

lo/4 

ioH  X  96  =    52-75  oxygen. 


100-00 


CALCULATION    OF   ANALYSIS.  845 

Returning  now  to  the  first  expression  of  the  relative  quantities,  which  was 
obtained  by  multiplying  the  relative  number  of  atoms  of  carbon,  oxygen,  and 
hydrogen  by  their  atomic  weights,  it  is  evident  by  dividing  the  relative  quantities 
by  the  atomic  weights,  the  relative  number  of  atoms  will  again  be  obtained: 

Parts  of  carbon 72  -5-  12  =    6  carbon  atoms. 

"     "  hydrogen 14  -s-    1  =  14  hydrogen  " 

"     "oxygen 96 -*- 16  =    6  oxygen      "       % 

It  is  moreover  evident  that  if  numbers  obtained  by  increasing  or  diminishing 
72,  14,  and  96  proportionally,  be  divided  by  12,  1,  and  16  respectively,  the 
resulting  quotients  will  express  the  atomic  ratio  also : 

100 
Carbon 72  X  ^n  =  39  '56  •*-  12  =  3 '296  carbon  atoms. 

lo<o 

100 
Hydrogen. ...  14  X  ~  =  '7 '69  -f-  1  =  7'690  hydrogen  " 

lo« 

100 
Oxygen 96  X  ~  =  52  '75  -f-  16  =  3 '296  oxygen  " 

loa 

182  100-00 

The  atomic  ratio  is  found  therefore  by  dividing  the  percentages  of  the  element* 
by  their  atomic  weights.  In  the  present  case,  the  formula  Cs.asoHT.eaoOs.ass 
expresses  the  relative  number  of  atoms. 

It  now  remains  to  find  the  smallest  whole  numbers  that  express  exactly,  or 
approximately,  the  same  atomic  ratio  as  those  directly  obtained  by  such  calcula- 
tion. This  is  usually  best  done  by  dividing  each  number  by  the  smallest,  and 
multiplying,  if  necessary,  the  resulting  quotients  by  some  number  that  will 
wholly  or  nearly  eliminate  their  fractional  parts : 

3-296  -s-  3-296  =  1         X  3  =  3 
7-690  -i-  3-296  =  2 '333  X  3  =  6 -999 
3-296  -T-  3-296  =  1         X  3  =  3. 

It  can  now  be  seen  that  3,  7,  3  are  the  smallest  whole  numbers  which  can 
express  the  relative  number  of  atoms  of  carbon,  hydrogen,  and  oxygen  respec- 
tively, i.e.,  that  C3H7O3  is  the  empirical  formula. 

When,  as  in  the  present  example,  the  percentage  composition  is  calculated 
from  a  formula,  the  empirical  formula  deduced  from  it  will,  of  course,  exhibit 
the  same  relative  number  of  atoms  as  the  original  formula,  except  the  slight 
variation  arising  from  neglecting  fractions  in  divisions.  But  when  the  empirical 
formula  is  deduced  from  a  percentage  composition  found  by  analysis,  it  cannot 
be  expected  that  the  calculated  atomic  ratio  can  be  expressed  exactly  by  small 
whole  numbers. 

OPPERM-A^N  found  by  actual  analysis  of  mannite : 

C 39  31 

H 7-71 

0 5298 

which,  calculated  as  above,  gives  C3.27«H7.7ioO3.3ii  as  the  first  formula.     Divid- 
ing each  number  by  the  least,  this  becomes  CiH2.353Oi.oio,  which  multiplied  by 


846  CALCULATION   OF   ANALYSIS. 

3  gives  CsHT.osgOs.oao.  These  last  numbers  show  that  the  carbon,  hydrogen, 
and  oxygen  atoms  found  by  analysis  are  so  nearly  in  the  proportion  3,  7,  3,  that 
it  is  reasonable  to  believe  that  C3H7O3  is  a  correct  empirical  formula,  and  that 
the  slight  differences  from  these  numbers  exhibited  by  the  numbers  actually 
obtained,  are  due  to  defects  inherent  in  the  method  of  analysis  used.  We 
can  judge  better  whether  such  differences  are  greater  than  may  be  due  to  error 
in  analysis  by  calculating  from  the  deduced  formula  the  percentage  composition 
which  it  requires  and  comparing  it  with  that  found.  The  composition  found 
may  also  be  compared  with  that  required  by  any  other  assumed  formula  which 
it  indicates  to  be  possible. 

Found.     Calculated  for  C3H7O3.    ForC4H9Ov 

Carbon 39'31  39'56  39'67 

Hydrogen 7'71  7'69  7'44 

Oxygen 52*98  52'75  52'89 

100-00  100-00  100-00 

2.  From  the  percentages  of  groups  of  elements  in  compounds, 
a.    When  isomoi^phous  constituents  are  not  present. 

In  the  analysis  of  oxygen  salts,  although  data  are  obtained  from  which  the 
percentage  of  each  element  or  each  radical  present  might  be  computed,  it  is  far 
more  convenient,  and  in  fact  customary,  to  calculate  the  percentage  of  oxides 
and  water  equivalent  in  quantity  to  the  elements  (see  §  67,  p.  131) 

For  example,  the  results  of  the  analysis  of  sodium  ammonium  phosphate 
were  presented  in  this  form : 

Na20        17-93 

(NH4)2O      15-23 

SO3          46-00 

H2O         20-84 


100-00 

From  this  statement  the  percentage  of  each  element  might  first  be  calculated, 
and  next  the  empirical  formula  by  the  method  already  described.  The  same 
end  may  be  attained  by  the  following  shorter  course. 

Applying  the  term  "molecule"  to  each  group  of  elements  here  presented,  it 
is  evident  that  the  relative  number  of  molecules  of  sodium  oxide,  ammonium 
oxide,  sulphuric  anhydride  and  water  can  be  found  by  dividing  the  quantity  of 
each  by  its  molecular  weight — a  process  the  same  in  principle  as  that  employed 
for  calculating  atomic  ratio  (p.  848). 


Relative  quantities. 
Na2O       17-93 

Molecular  weights.       Relative  number  of  molecules. 
-r-      62-08      =        -2888      H-      -2888      =      1 

(NH4)20 
S03 

15-23 
46-00 

•4- 

52-08 
80- 

=  -2928 
=  -5750 

-f- 

•2888 
•2888 

=  1-01 

=  1-99 

H2O 

20-84 

-=- 

18- 

=  1-1577 

4- 

•2888 

=  4-00 

The  numbers  1,  I'Ol,  1-99,  4,  are  so  nearly  in  the  same  proportion  as  1,  1,  2,  4, 
that  there  can  be  no  doubt  that  (Na2O)i(NH4)2O)1(SO3)2(H2O)4  is  a  correct 
formula.  This  formula  shows  necessarily  the  same  grouping  of  elements  that 
was  used  in  stating  .the  percentage  composition.  Rearranging  the  order  in 
which  the  symbols  of  the  elements  stand,  (Na2O)1(NH4)2O)1(SO3)2(H2O)4  = 


CALCULATION    OF    ANALYSIS.  847 

Na2N2S2Hi6Oi2,  and  dividing  by  2,  we  obtain  the  strictly  empirical  formula 
NaNSHgOe. 

Hational  formula.. — Having  obtained  the  empirical  formula  of  a  compound, 
any  theoretical  conclusion  regarding  its  molecular  weights  may  be  expressed  by 
increasing  (if  necessary)  each  atom  an  equal  number  of  times;  and  any  supposi- 
tion, suggestion,  or  conclusion  regarding  its  chemical  constitution  may  be 
expressed  by  a  conformable  arrangement  of  the  atoms.  From  the  empirical 
formulae  of  most  oxygen  salts  rational  formulae  may  be  readily  deduced.  In 
the  above  case,  for  instance  (sodium  ammonium  sulphate),  NaNSH8O6  = 
NaNH4SO2H4O4;  a  rational  formula  implying  that  the  nitrogen  exists  in  the 
form  of  ammonium  and  the  sulphur  in  the  form  of  the  acid  radical  SO2 
(sulphuryl). 

By  inspection  of  the  component  parts  of  this  formula  it  is  seen  that  the  sum 
of  the  quantivalence  of  the  two  basic  radicals  Na'  and  (XH4)'  equals  that  of  the 
acid  radical  (SO2)".  The  salt  must  therefore  be  a  normal  salt,  and  none  of  the 
hydrogen  can  be  in  combination  with  either  basic  or  acid  radical.  Two  atoms 
of  oxygen  are  required  to  unite  the  radicals,  leaving  (HaO)2.  This  leads  to  the 
conclusion  that  the  4  atoms  of  hydrogen  exist  in  the  form  of  water,  which  is  in 
a  state  of  combination  called  water  of  crystallization — 

NaNH4SO2H4O4  =  ^  ~Q>  s°2  +  2H2O. 

b.    When  isomorphous  constituents  are  present. 

In  deducing  formulae,  it  must  be  borne  in  mind  that  closely  related  elements 
or  radicals,  more  especially  the  basic  metals,  may  replace  each  other  in  all  pro- 
portions. Elements  of  like  quantivalence  are  oftenest  found  replacing  each 
other,  but  in  some  cases  equivalent  amounts  of  elements  having  different  valence 
appear  to  replace  each  other.  The  following  example  will  illustrate  the  kind 
of  formula  and  method  of  deducing  it  commonly  used  in  such  cases. 

S.  L.  PENFIELD  found  by  analysis  of  triphylite  the  following  composition: 

Molecular  weights.  Mol.  ratio.  At.  ratio. 

P205  44-76     -h     142  =  -315  X     2     =     P          '630 

FeO  26-40     -r-      72  =  '366  Fe         '3661 

MnO  17-84     -*-      71  =  '251  Mn       '251  I    _  ™  .AQQ 

CaO  -24     -r-      56  =  '004  Ca        '004  { 

McrO  -47-^-40  =  -012  Mg       -012  J 

Li2O  9-36     -f-      30  =  -312  X     2    =     Li          '624  f   _  «,  .„». 

XaaO  -35     -T-      78-08  =  '005  X     2     =     Na        '010  f  = 

H20  -42  O  2-525 


99-84 

Disregarding  the  small  amount  of  water,  the  relative  numbers  of  molecules 
of  the  oxides  (mol.  ratio)  are  first  found  by  dividing  quantities  by  molecular 
weights,  as  in  the  preceding  example.  Next  the  atoms  contained  by  the  mole- 
cules are  written  in  another  column  (at.  ratio).  This  column,  icith  the  adjoined 
symbols,  is  the  empirical  formula.  It  is  apparent,  or  can  be  proved  by  trial,  that 
the  numbers  of  different  atoms  are  not  in  any  simple  ratio.  Such  an  atomic 
relation  is  to  be  expected  when  isomorphous  constituents  are  present.  It 
remains  now  to  unite  the  atoms  of  such  elements  as  are  supposed  to  be  capable 
of  mutually  replacing  each  other,  and  ascertain  whether  the  numbers  thus 


848  CALCULATION   OF   ANALYSIS. 

obtained  are  in  any  simple  proportion.  For  this  purpose  let  R"  represent  one 
atom  of  any  dyad  basic  metal  and  R'  one  atom  of  any  monad  basic  metal  present. 
The  sum  of  the  dyad  atoms  is  '633  ;  that  of  the  monad  atoms,  '634,  as  above  shown. 
The  atomic  ratio  thus  obtained  is  expressed  by  the  formula  R"633R'634P63oO25i5; 
or  simpler,  dividing  by  630,  almost  exactly  by  R"R'PO4  which  is  equal  to 


\0-R', 

anhydrous  normal  lithium  ferrous  phosphate  in  which  iron  is  partially  replaced 
by  manganese,  magnesium,  and  calcium;  and  lithium  to  a  slight  extent  by 
sodium. 

It  may  be  here  observed  that  in  presenting  atomic  ratios  in  connection  with 
analyses  of  natural  oxygen  salts  (minerals),  computation  and  statement  of 
oxygen  atoms  is  often  omitted,  since  they  may  be  deduced  from  a  formula  show 
ing  the  other  constituents.  Omitting  oxygen  in  the  above  example  we  have 
R"R'P.  By  referring  to  the  percentage  composition  it  is  seen  that  for  two  P 
five  O  must  be  present,  —  for  two  R'  one  O,  —  for  one  R"  one  O.  Doubling 
R"R'P  and  appending  to  each  constituent  the  required  oxygen  atoms,  we  have  : 
R%O2R'2OPaO6  =  R"2R'aP2O8,  and  dividing  by  2,  R"RTO4,  as  before. 


TABLES  FOR  THE  CALCULATION  OF  ANALYSIS. 


TABLE  I. 

ATOMIC  WEIGHTS  OF  THE  ELEMENTS  CONSIDERED  IN  THE  PRESENT  WORK.* 


Aluminium 

Antimony 

Arsenic 

Barium 

Bismuth 

Boron 

Bromine 

Cadmium 

Caesium 

Calcium 

Carbon 

Chlorine 

Chromium 

Cobalt 

Copper 

Fluorine 

Gold 

Hydrogen 

Iodine 

Iron 

Lead 

Lithium 


Alt 

Sbf 

As 

Ba 

Bi 

B 

Br 

Cd 

Cs 

Ca 

C 

Cl 

Cr 

Co 

Cu 

Fl 

Au 

H 

I 

Fe 

Pb 

Li 


27-50 

122-00 

75-00 

137-00 

208-00 

11-00 

79-95 

112-00 

133-00 

40-00 

12-00 

35-46 

52-48 

59-00 

63-40 

19-00 

196-71 

1-00 

126-85 

56-00 

207-00 

7-00 


i  I  Magnesium 
!  Manganese 
|  Mercury 

Molybdenum 

Nickel 
;  Nitrogen 

Oxygen 

Palladium 

Phosphorus 

Platinum 

Potassium 
,  Rubidium 

Selenium 

Silicon 

Silver 

Sodium 

Strontium 

Sulphur 

Tin 

Titanium 

Uranium 
.Zinc 


Mg 

Mn 

Hg 

Mo 

Ni 

N 

O 

Pd 

P 

Pt 

K 

Rb 

Se 

Si 


Sr 

S 

Sn 

Ti 

Ur 

Zn 


24-00 
55-00 

200-00 
92-00 
59-00 
14-04 
16-00 

106-58 
31-00 

19718 
39-13 
85-40 
79-00 
28-00 

107-93 
23-04 
8750 
32-00 

118-00 
50-00 

237-60 
65-06 


TABLE  II 


COMPOSITION  OF   THE  BASIC  AND  ACID  OXIDES. 


GROUP  I. 


a.   BASIC  OXIDES. 


Caesia Csa. 

O.. 


Cs2O. 


.266-00 94-33 

.  16-00..  5-67 


.282-00..         ..100-00 


Rubidia Rba. 

O.. 


.170-80 91-43 

.  16-00..  8-57 


Rb2O 186.80..         ..100.00 


*  [The  numbers  here  given  are  based  on  the  atomic  weights  used  in  the  sixth  German 
edition,  the  atomic  weights  of  the  "old  system"  being  doubled  when  necessary.] 

t  Recent  critical  investigations— by  J.  P.  COOKE,  on  the  atomic  weight  of  antimony— by 
J.  W.  MALLET,  on  that  of  aluminium,  have  conclusively  shown  that  120  and  27'02  respectively 
should  be  taken  as  the  atomic  weights  of  these  elements.  See  Transactions  of  Am.  Acad. 
Sci.,  13, 15.  Atomic  Weight  of  Antimony,  and  Philosophical  Transactions  of  the  Royal  Society 
(London),  Revision  of  the  Atomic  Weight  of  Aluminium. 


850  TABLE   II. 

Potassa Ka 78*26 83-03 

O..  .  16-00..  .  16-97 


KaO 94-26 100-00 

Soda Naa 46-08 74-23 

O..  .  16-00..  .  25-77 


NaaO  .................  62-08  ........  100-00 


..<  ......................  Li2  ...................  14-00  ........  46-67 

0  .....................  16-00  ........  53-33 

Li3O  ..................  30-00  .......  .100-00 

Ammonium  oxide  .................  (NH4)»  ................  36-16  .......  .  69-28 

O..  .  16-00..  .  30-72 


(NH4)aO 52-16 ...100-00 

GBOUP  II. 

Baryta Ba 137-00 89-54 

O..  .  16-00..  .  10-46 


BaO 153-00 100-00 

Strontia Sr 87-50 84-54 

O..  .  16-00..  .  15-46 


SrO 103-50 100-00 

Lime Ca 40-00 71-43 

O..  .  16-00..  .  28-57 


CaO 56-00 100-00 


Mg 24-00 60-03 

0 16-00 39-97 

MgO... 40-00 100-00 

GROUP  III. 

Alumina Ala 55'00 53-40 

O, 48-00..  .  46-60 


AlaO3 103-00 100-00 

Chromic  oxide Cra 104-96 68*62 

O3..  .  48-00..  .  31-38 


CraO3 152-96 100-00 

GKOUP  IV. 

Zinc  oxide Zn 65*06 80-26 

O..  .  16-00..  .  19-74 


ZnO 81-06..         ..100-00 


TABLE   II.  851 

Manganous  oxide Mn  55-00 77-46 

O. .  .  16-00..  .  22-54 


MnO 71-00 ...100-00 

Manganic  oxide Mn3 110-00 69-62 

O, ..  48-00 30-38 


Mn,O3 158-00 100-00 

Nickelous  oxide , Ni 59-00 78-67 

0 16-00 21-33 

NiO 75-00 100-00 

Cobaltous  oxide Co 59-00 78-67 

O .  16-00..          .  21-33 


CoO 75-00 100-00 

Cobaltic  oxide Co, 118-00 71-08 

Os..  .  48-00  .  .  28-92 


Co,O, 166-00 100-00 

Ferrous  oxide Fe 56-00 77-78 

O..  .  16-00.. 


FeO 72-00 100-00 

Ferric  oxide Fea 112-00 70-00 

Os .  48-00..  .  30-00 


Fe2O, 160-00 100-00 

GROUP  V. 

Silver  oxide Aga 215*86 93-10 

O .  16-00..  ,    6-90 


AgaO 231-86 100-00 

Lead  oxide Pb 207-00 92-83 

O .  16-00..  7-17 


PbO 223-00 100-00 

Mercurous  oxide Hga 400-00 96-15 

O..  .  16-00..  3-85 


HgaO 416-00 100-00 

Mercuric  oxide Hg 200-00 92-59 

O. .  .  16-00..  7-41 


HgO 216-00 100-00 


852  TABLE   II. 

Cuprous  oxide Cu2 126*80 88-80 

O .  16-00..          .  11-20 


CuaO 142-80 100-00 

Cupric  oxide Cu 63-40 79-85 

O..  .  16-00..          .  20-15 


CuO 79-40 100-00 

Bismuth  trioxide Bia 416-00 89-66 

O3 48-00 10-34 


Bi2O3 464-00 100-00 

Cadmium  oxide Cd 112-00 87-50 

O..  .  16-00..  .  12-50 


CdO 128-00 100-00 

GROUP  VI. 

Auric  oxide Au2 392-00 89-09 

O3 48-00 10-91 


Au2O3 440-00 100-00 

Platinic  oxide Pt 197-18 86-04 

O2 32-00 13-96 

PtO2 229-18 100-00 

Antimonious  oxide Sba 244-00 83-56 

O3...  48-00 16-44 


Sb2O3 292-00 100-00 

Stannous  oxide Sn 118-00 88'06 

O...  .  16-00 11-94 


SnO 134-00 100-00 

Stannic  oxide Sn 118*00 78 -67 

O2 32-00 21-33 

SnO2 150-00  100-00 

Arsenious  oxide As2 150-00 75-76 

O3 48-00 24-24 

As2O3 198-00 100-00 

Arsenic  oxide As2 150-00 65-22 

O5 80-00 34-78 

As205...  ..230-00 100-00 


TABLE    II.  853 

b.  ACID  OXIDES  (ANHYDRIDES). 

Chromic  anhydride Or 52*48 52-23 

O3...                                .  48-00..           .  47-77 


CrO3 100  48 100-00 

Sulphuric  anhydride S 32-00 40 -.00 

O3...  .  48-00..  .  60-00 


SO3 80-00 100-00 

Phosphoric  anhydride P3 62-00 43'66 

O6 80-00 56-34 


PaO5 142-00 100-00 

Boracic  anhydride B3 22-00. .......  31-43 

O3 48-00..  .  68-57 


B3O3 70-00 100-00 

Oxalic  anhydride C3 24-00 33-33 

O3 48-00 66-67 

C3O3 72-00 100-00 

Carbonic  anhydride C 12-00 27-27 

Oa 3200 72-73 


CO3 44-00 100-00 

Silicic  anhydride Si 28-00 46-67 

O2 32-00 53-33 


SiO3  ...........  .......  60-00  ........  100-00 

Nitric  anhydride  .................  Na  ....................  28-08  ........  25-98 

.      O6....  ................  80-00  ........  74-02 


108-08  ........  100-00 


Chloric  anhydride.  ...............  C13  ................  ...  70  92  .......  46*99 

O6  ....................  80-00  ........  53-01 

C1,O...  ..150-92..         ..100-00 


854  TABLE   III. 


TABLE   III. 

REDUCTION    OF    COMPOUNDS    FOUND    TO    CONSTITUENTS    SOUGHT    BY    SIMPLE 
MULTIPLICATION    OR    DIVISION. 

This  Table  contains  only  some  of  the  more  frequently  occurring  compounds 
the  formulae  preceded  by  !  give  absolutely  accurate  results. 

FOR  INORGANIC  ANALYSIS. 

CARBON  DIOXIDE. 
!  Calcium  Carbonate  X  0.44  =  Carbon  dioxide. 

CHLORINE. 

Silver  chloride  X  0'2473  =  Chlorine. 

COPPER. 
Cupric  oxide  X  0-79849  =  Copper. 

IRON. 

!  Ferric  oxide  X  0'7  =  Iron. 
!  Ferric  oxide  X  0'9  =  Ferrous  oxide. 

LEAD. 
Lead  oxide  X  0*9283  =  Lead. 

MAGNESIA. 

Magnesium  pyrophosphate  X  0  *36036  =  Magnesia. 

MANGANESE. 

Protosesquioxide  of  manganese  X  0-72052  =  Manganese. 
Protosesquioxide  of  manganese  X  0 '9301 3  =  Manganous  oxide. 

PHOSPHORIC   ANHYDRIDE   (P2O8). 

Magnesium  pyrophosphate  X  0'6396  =  Phosphoric  acid. 
Uranyl  pyrophosphate  ((UO2)3P2O7)  X  01991  .-=  PaO6. 

POTASSIUM. 

Potassium  chloride  X  0'5246    =  Potassium. 
Potassium  sulphate  X  0 '54092  =  Potassa. 
Potassium  platinic  chloride  X  0*30557. 

or 
Potassium  platinic  chloride  Potassium  chloride. 

3-2725 

Potassium  platinic  chloride  X  019308  1 

or  I   _ 

Potassium  platinic  chloride 
5-179 


TABLE   III. 


SODA. 

Sodium  chloride  X  0'5306    =  Soda. 
Sodium  sulphate  X  0-43694  =  Soda. 

SULPHUR. 

Barium  sulphate  X  0 '13734  =  Sulphur. 

SULPHURIC  ACID. 

Barium  sulphate  X  0'34335  =  Sulphuric  anhydride  (S0»). 
FOR  ORGANIC  ANALYSIS. 

CARBON. 

Carbon  dioxide  X  0'2727 

or 
Carbon  dioxide 


855 


3-666 

or 
Carbon  dioxide  X  3 


=  Carbon. 


11 

HYDROGEN. 


Water  X  O'lllll 

or 
Water 


NITROGEN. 


Ammonium  platinic  chloride  X  0 -06296  =  Nitrogen. 
Platinum  X  01424  =  Nitrogen. 


856 


TABLE  IV. 


TABLE 

Showing  the  Amount  of  the 
Number  of  the 


Elements. 

Found. 

Sought. 

1 

Aluminium  .  . 
(Ammonium). 

Alumina 
A12O3 
Ammonium  chloride 
NH4C1 
Ammonium  platinic  chloride 
(NH4Ciy  PtCl4 

Aluminium 
Al 
Ammonia 
NH3 
Ammonium  oxide 
(NH4)20 

0.53398 
0.31850 
0.11677 

Antimony.  .  .  . 

Ammonium  platinic  chloride 
(NH4Cl)2-PtCl4 
Antimonious  oxide 
Sb2O3 
Antimonious  sulphide 
Sb2S3 

Ammonia 
NH3 
Antimony 
Sb 
Antimony 
Sb 

0.07641 
0.83562: 
0.71765 

Arsenic.  .  .  . 

Antimonious  sulphide 
Sb8S3 
Antimony  tetroxide 
Sb204 
Arsenious  oxide 
As2O3 

Antimonious  oxide 
Sb2O3 
Antimonious  oxide 
Sb203 
Arsenic 
As 

0.85882' 
0.94805 
0.  7575$ 

Arsenic  oxide 
As2O5 

Arsenic  oxide 
As2O6 
Arsenious  sulphide 

As2S3 

Arsenic 
As 
Arsenious  oxide 
As2O3 
Arsenious  oxide 
As2O3 

0.65217 
0.86087 
0.80488- 

Barium  

Arsenious  sulphide 
As2S3 
Baryta 

Arsenic  oxide 
As2O5 
Barium 

0.93496. 
0  89542 

BaO 
Barium  sulphate 
BaSO4 

Ba 
Baryta 
BaO 

0.65665 

TABLE  IV. 


85T 


IV. 

Constituent  sought  for  every 
Compound  found. 


*  1  • 

4 

5 

0 

7 

8 

9 

1.06796 
0.63701 
0.23353 

1.60194 
0.95551 
0.35030 

2.13592 
1.27402 
0.46706 

2.66990 
1.59252 
0.58383 

3.20389 
1.91103 
0.70060 

3.73787 
2.22953 
0.81736 

4.27185 
2.54804 
0.93413 

4.80583 
2.86654 
1.05089' 

0.15282 
1.67123 
1.43529 

0.22923 

2.50685 
2.15294 

0.30564 
3.34247 
2.87059 

0.38205 
4.17808 
3.58834 

0.45846 
5.01370 
4.30588 

0.53487 
5.84932 
5.02353 

0.61128 
6.68194 
5.74118 

0.68769 
7.52055 
6.45882 

1.71765 
1.89610 
1.51516 

2.57647 
2.84416 
2.27274 

3.43530 
3.79221 
3.03032 

4.29412 
4.74026 
3.78790 

5.15294 
5.68831 
4.54548 

6.01177 
6.63636 
5.30306 

6.87059 
7.58442 
6.06064 

7.72942 
8.53247 
6.81822 

1.30435 
1.72174 
1.60975 

1.95652 
2.58261 
2.41463 

2.60870 
3.44348 
3.21951 

3.26087 
4.30435 
4.02439 

3.91304 
5.16521 
4.82927 

4.56522 
6.02608 
5.63415 

5.21739 
6.88695 
6.43902 

5.86957 

7.74782 
7.24390 

1.86992 
1.79085 
1.31330 

2.80488 
2.68627 
1.96996 

3.73984 
3.58170 
2.62661 

4.67480 
4.47712 
3.28326 

5.60975 
5.37255 

3.93991 

6.54471 
6.26797 
4.59656 

7.47967 
7.16340 
5.25322 

8.41465 
8.05882" 
5.9098T 

858 


TABLE   IV. 


TABLE  IV. 


Elements. 


Found. 


Sought. 


Barium. 


Bismuth 


Boron 

Bromine... 
Cadmium. . . 


Calcium. . . 


Carbon 


Chlorine... 


Chromium . 


Cobalt. 


Barium  carbonate 

BaCO3 
Barium  silico-fluoride 

BaFVSiFl4 

Bismuth  tri  oxide 

Bi2O3 


Boracic  anhydride 

Ba03 
Silver  bromide 

AgBr 

Cadmium  oxide 
CdO 


Lime 
CaO 
Calcium  sulphate 

CaSO4 
Calcium  carbonate 

CaCO3 


Carbonic  acid 

C02 
Calcium  carbonate 

CaCO3 

Silver  chloride 
AgCl 


Silver  chloride 

AgCl 
Chromic  oxide 

CraO3 
Chromic  oxide 

Cr2O3 


Lead  chromate 

PbCrO4 

Cobalt 

Co 

Cobaltous  sulphate 
CoSO4 


Baryta 

BaO 
Baryta 

BaO 

Bismuth 

Bi 


Boron 

B 

Bromine 
Br 

Cadmium 
Cd 


Calcium 

Ca- 
Lime 
CaO 
Lime 
CaO 


Carbon 

C 
Carbonic  acid 

CO2 

Chlorine 
Cl 


Hydrochloric  acid 

HC1 
Chromium 

Cr 

Chromic  anhydride 
CrO3 


Chromic  anhydride 

Cr03 
Cobaltous  oxide 

CoO 
Cobaltous  oxide 

CoO 


TABLE   IV. 


859 


•(Continued). 


2 

3 

4 

5         *         7 

8        9 

1.55330 

2.32995 

3.10660 

3.88325   4.65990 

5.43655 

6.21320 

6.98985 

1.09677 

1.64516 

2.19355 

2.74194 

3.29032 

3.83871 

4.38710 

4.93548 

1.79310 

2.68965 

3.58620 

4.48275 

5.37930 

6.27586 

7.17240 

8.06895 

0.62857 

0.94286 

1.25714 

1.57143 

1.88572 

2.20000 

2.51429 

2.82857 

0.85107 

1.27661 

1.70215 

2.12768 

2.55322 

2.97876 

3.40430 

3.82983 

1.75000 

2.62500 

3.50000 

4.37500 

5.25000 

6.12500 

7.00000 

7.87500 

1.42857 

2.14286 

2.85714 

3.57143 

4.28571 

5.00000 

5.71429 

6.42857 

0.82353 

1.23529 

1.64706 

2.05882 

2.47059 

2.88235 

3.29412 

3.70588 

•L  12000 

1.68000 

2.24000 

2.80000 

3.36000 

3.92000 

4.48000 

5.04000 

0.54546 

0.81818 

1.09091 

1.36364 

1.63636 

1.90909 

2.18181 

2.45455 

0.88000 

1.32000 

1.76000 

2.20000 

2.64000 

3.08000 

3.52000 

3.96000 

0.49460 

0.74188 

0.98919 

1.23649 

1.48378 

1.73108 

1.97838 

2.22568 

0.50854 

0.76281 

1.01708 

1.27135 

1.52563 

1.77990 

2.03417 

2.28844  * 

1.37238 

2.05858 

2.74477 

3.43096 

4.11715   4.80334 

5.48954 

6.17573 

2.62762 

3.94142 

5.25523 

6.56904 

7.88285 

9.19666 

10.51046 

11.82427 

0.62124 

0.93187 

1.24249 

1.55311 

1.86373 

2.17435 

2.48498 

2.79560 

2,54237 

3.81356 

5.08474 

6.35593 

7.62712 

8.89830 

10.16949 

11.44067 

0.96774 

1.45161 

1.93548 

2.41935 

2.90323 

3.38710 

3.87097 

4.35484 

860 


TABLE  IV. 


TABLE  IV. 


Elements. 


Found, 


Sought. 


Cobalt 


Copper 


Fluorine. 


Hydrogen. 
Iodine. . . . 


Iron 


Lead 


Lithium.. 


Cobaltous  sulphate  +  potassium 

sulphate 

2(CoSO4)  -|-  3(K2SO4) 
Cobaltous  sulphate  +  potassium 

sulphate 
2(CoSO4)-f  3(K3SO4) 


Cupric  oxide 

CuO 
Cuprous  sulphide 

Cu2S. 
Calcium  fluoride 

CaFl2 


Silicon  fluoride 

SiFl4 

Water 

H2O 

Silver  iodide 
Agl 


Palladious  iodide 

PdI3 
Ferric  oxide 

Fe2O3 

Ferric  oxide 
Fe203 


Ferrous  sulphide 

FeS 
Lead  oxide 

PbO 

Lead  sulphate 
PbS04 


Lead  sulphate 

PbSO4 
Lead  sulphide 

PbS 

Lithium  carbonate 
Li2Co3 


Cobaltous  oxide 
CoO 

Cobalt 
Co 


Copper 

Cu 
Copper 

Cu 
Fluorine 

Fl 


Fluorine 

Fl 
Hydrogen 

H 

Iodine 
I 


Iodine 

I 

Iron 
Fe 

Ferrous  oxide 
FeO 


Iron 

Fe 
Lead 

Pb 

Lead  oxide 
PbO 


Lead 
Pb 

Lead  oxide 
PbO 

Lithia 
Li20 


TABLE   IV 


861 


(Continued). 


2 

3 

45678 

9 

0.36024 

0.54036 

0.72048      0.90060      1.08072      1.26084 

1.44096 

1.62108 

0.28339 

0.42508 

0.56676 

0.70847 

0.85016 

0.99186 

1.13355 

1.27525 

1.59698 

2.39547 

3.19396 

3.99244 

4.79093 

5.58942 

6.38791 

7.18640 

1.59698 
0.97436 

2.39547 
1.46154 

3.19396 
1.94872 

3,99244 
2.43590 

4.79093 
2.92307 

5.58942 
3.41027 

6.38791 
3.89743 

7.18640 
4.38461 

1.46154 

2.19231 

2.92308 

3.65385 

4.38461 

5.11538 

5.84615 

6.57692 

0.22222 

0.33333 

0.44444 

0.55555 

0.66667 

0.77778 

0.88889 

1.00000 

1.08059 

1.62088 

2.16118 

2.70147 

3.24176 

3.78206 

4.32235 

4.86264 

1.40835 

2.11252 

2.81670 

3.52087 

4.22505 

4.92922 

5.63340 

6.33757 

1.40000 
1.80000 

2.10000 
2.70000 

2.80000 
3.60000 

3.50000 
4.50000 

4.20000 
5.40000 

4.90000 
6.30000 

5.60000 
7.20000 

6.30000 
8.10000 

1.27273 

1.90909 

2.54546 

3.18182 

3.81818 

4.45455 

5.09091 

5.72728 

1.85650 

2.78475 

3.71300 

4.64126 

5.56951 

6.49776 

7.42601 

8.35426 

1.47195 

2.20792 

2.94390 

3.67987 

4.41584 

5.15182 

5.88779 

6.62377 

1.36634 

2.04950 

2.73267 

3.41584 

4.09901 

4.78218 

5.46534 

6.14851 

1.86611 
0.81081 

2.79916      3.73222 
1.21622  :    1.62162 

4.66527 
2.02703 

5.59832 
2.43243 

6.53138 

2.83784 

7.46443 
3.24324 

8.39749 
3.64865 

862 


TABLE   IV 


TABLE  IV. 


Elements. 


Found. 


Sought. 


Lithium 


Magnesium. 


Manganese. 


Mercury 


Nickel... 
Nitrogen. 


Lithium  sulphate 

Li2SO4 

Lithium  phosphate 

Li3PO4 

Magnesia 

MgO 


Magnesium  sulphate 

MgS04 
Magnesium  pyrophosphate 

Mg2P2O7 

Manganous  oxide 

MnO 


Protosesquioxide  of  manganese 
MnO  +  Mn203 
Manganic  oxide 

Mn2O3 

Manganous  sulphate 
MnS04 


Manganous  sulphide 

MnS 
Manganous  sulphide 

MnS 

Mercury 

Hg 


Mercury 

Hg 
Mercurous  chloride 

Hg2Cl2 

Mercuric  sulphide 
HgS 


Nickelous  oxide 

NiO 

Ammonium  platinic  chloride 

(NH4C1)2,  PtCl4 

Platinum 

Pt 


Lithia 

Li20 
Lithia 

Li2O 
Magnesium 

Mg 


Magnesia 

MgO 
Magnesia 

MgO 

Manganese 
Mn 


Manganese 

Mn 
Manganese 

Mn 
Manganous  oxide 

MnO 


Manganous  oxide 

MnO 
Manganese 

Mn 

Mercurous  oxide 
Hg20 


Mercuric  oxide 

HgO 
Mercury 

MHg 

Mercury 
Hg 


Nickel 

Ni 
Nitrogen 

N 
Nitrogen 

N 


TABLE   IV. 


863 


( Continued}. 


2 

3 

4 

5 

• 

7 

8        9 

; 

0.54545 

0.81818 

1.09091 

1.36364  !  1.63636 

1.90909 

2.18182   2.45454 

0.77586 

1.16379 

1.55172 

1.93966   2.32759 

2.71552 

3.10345   3.49138 

1.20061 

1.80091 

2.40121 

3.00151 

3.60182 

4.20212 

4.8024-2 

5.40273 

0.66700 

1.00051 

1.33401 

1.66751 

2.00101 

2.33451 

2.66802 

3.00152 

0.72072   1.08108 

1.44144 

1.80180 

2.16216 

2.52252 

2.88288 

3.24324 

1.54930 

2.32394 

3.09859 

3.87324 

4.64789 

5.42254 

6.19718 

6.97183 

1.44105 

2.16157 

2.88210 

3.60262 

4.32314 

5.04367 

5,76419 

6.48472 

1.39241 
0.94040 

2.08861 
1.41060 

2.78481 
1.88080 

3.48102 
2.35099 

4.17722 
2.82119 

4.87342 
3.29139 

5.56962 
3.76159 

6.26583 
4.23179 

1.63218 

2.44828 

3.26437 

4.08046 

4.89655 

5.71264 

6.52874 

7.34483 

1.26437 

1.89655   2.52874 

3.16092 

3.79310 

4.42529 

5.05747 

5.68966 

2.08000 

3.12000 

4.16000 

5.20000 

6.24000 

7.28000 

8.32000 

9.36000 

2.16000 

3.24000 

4.32000 

5.40000 

6.48000 

7.56000 

8.64000 

9.72000 

1.69880 

2.54820 

3.39760 

4.24701 

5.09641 

5.94581 

6.79521 

7.64461 

1.72414 

2.58621 

3.44828 

4.31034 

5.17241 

6.03448 

6.89655 

7.75862 

1.57333 

0.12591 

2.36000 

0.18887 

3.14667 
0.25182 

3.93333 
0.31478 

4.72000 
0.37774 

5.50667 
0.44069 

6.29334 
0.50365 

7.08000 
0.56660 

0.28482 

0.42722 

0.56963 

0.71204   0.85445   0.99686 

1.13926 

1.28167 

864 


TABLE   IV. 


TABLE  IV. 


Elements. 


Found. 


Sought. 


Nitrogen. . . 
Oxygen 


Silver  cyanide 

AgCN 
Silver  cyanide 

AgCN 
Alumina 

A12O3 


Antimonious  oxide 

Sb2O3 
Arsenious  oxide 

As2O3 

Arsenic  oxide 
As2O5 


Baryta 

BaO 
Bismuth  trioxide 

Bi203 
Cadmium  oxide 

CdO 


Chromic  oxide 

Cr203 
Cobaltous  oxide 

CoO 

Cupric  oxide 
CuO 


Ferrous  oxide 

FeO 
Ferric  oxide 

Fe2O3 

Lead  oxide 

PbO 


Lime 

CaO 

Magnesia 

MgO 

Manganous  oxide 
MnO 


Cyanogen 

CN 

Hydrocyanic  acid 
flCN 


Oxygen 

O 
Oxygen 

O 


Oxygen 

O 
Oxygen 


Oxygen 


Oxygen 
O 
;n 


Oxygen 

O 
Oxygen 

O 
Oxygen 

O 


TABLE  IV. 


865 


(Continued). 


2 

3 

4 

5 

6 

j 

7 

8 

9 

0.38874 
0.40367 
0.93204 

0.58312 
0.60551 
1.39806 

0.77749 
0.80734 
1.86408 

0.97186 
1.00918 
2.33010 

1.16623 
1.21102 
2.79611 

1.36060 
1.41285 
3.26213 

1.55498 
1.61469 
3.72815 

1.74935 
1.81652 
4.19417 

0.32877 
0.48484 
0.69565 

0.49315 
0.72726 
1.04348 

0.65754 
0.96968 
1.39130 

0.82192 
1.21210 
1.73913 

0.98630 
1.45452 
2.08696 

1.15069 
1.69694 
2.43478 

1.31507 
1.93936 
2.78261 

1.47946 
2.18178 
3.13043 

0.20915 
0.20690 
0.25000 

0.31373 
0.31035 
0.37500 

0.41830 
0.41380 
0.50000 

0.52288 
0.51725 
0.62500 

0.62745 
0.62070 
0.75000 

0.73203 
0.72415 
0.87500 

0.83660 
0.82760 
1.00000 

0.94118 
0.93105 
1.12500 

0.62762 
0.42667 
0.40302 

0.94143 
0.64000 
0.60453 

1.25524 
0.85333 
0.80604 

1.56905 
1.06667 
1.00756 

1.88286 
1.28000 
1.20907 

2.19667 
1.49333 
1.41058 

2.51048 
1.70666 
1.61209 

2.82429 
1.92000 
1.81360 

0.44444 
0.60000 
0.14350 

0.66667 
0.90000 
0.21525 

0.88889 
1.2000Q 
0.28700 

1.11111 
1.50000 
0.35874 

1.33333 
1.80000 
0.43049 

1.55555 
2.10000 
0.50224 

1.77778 
2.40000 
0.57399 

2.00000 
2.70000 
0.64574 

0.57143 
0.79939 
0.45070 

0.85714 
1.19909 
0.67606 

1.14286 
1.59879 
0.90141 

1.42857 
1.99849 
1.12676 

1.71429 
2.39818 
1.35211 

2.00000 
2.79788 
1.57746 

2.28571 
3.19758 
1.80282 

2.57143 
3.59727 

2.02817 

866 


TABLE   IV. 


TABLE  IV. 


Elements. 


Found. 


Sought. 


Oxygen. 


Phosphorus... 


Protosesquioxide  of  Manganese 
MnO  +  Mn2O3 
Manganic  oxide 

Mn2O3 

Mercurous  oxide 
Hg20' 


Mercuric  oxide 

HgO 
Niekelous  Oxide 

NiO 
Potassa 

K2O 


Silicic  anhydride 

Si02 

Silver  oxide 
Ag2O 
Soda 
Na2O 


Strontia 

SrO 

Stannic  oxide 

SnO2 

Water 

H2O 


Zinc  oxide 

ZnO 
Phosphoric  anhydride 

P205 

ium  pyrophosphate 
Mg2P207 


Ferric  phosphate 

FeP04 
Silver  phosphate 

Ag3PO4 

Uranyl  pyrophosphate 
(U02)2P207 


;en 


Oxygen 
Oxygen 


Oxygen 

Oxygen 
O 


Oxygen 

O 
Oxygen 

Oxygen 
O 


Oxygen 
Oxygen 

Oxygen 
O 


Oxygen 

Phosphorus 

P 

Phosphoric  anhydride 
P205 


Phosphoric  anhydride 

P205 
Phosphoric  anhydride 

P206    * 
Phosphoric  anhydride 

P205 


TABLE   IV. 


867 


(Continued). 


2         3 

4 

5 

6 

7 

8 

9 

0.55895   0.83843   1.11790 

1.39738 

1.67686 

1.95633 

2.23581 

2.51528 

0.60759   0.91139 

1.21519 

1.51899 

1.82278 

2.12658 

2.43038 

2.73417 

0.07692 

0.11539 

0.15385 

0.19231 

0.23077 

0.26923 

0.30770 

0.34616 

0.14815 

0.22222 

0.29630 

0.37037 

0.44444 

0.51852 

0.59259 

0.66667 

0.42667 

0.64000 

0.85333 

1.06667 

1.28000 

1.49333 

1.70667 

1.92000 

0.33949 

0.50923 

0.67897 

0.84871 

1.01846 

1.18820 

1.35794 

1.52768 

1.06667 

1.60000 

2.13333 

2.66667 

3.20000 

3.73333 

4.26667 

4.80000 

0.13801 

0.20702 

0.27603 

0.34503 

0.41404 

0.48305 

0.55206 

0.62106 

0.51546 

0.77320 

1.03093 

1.28866 

1.54639 

1.80412 

2.06186 

2.31959 

0.30918 

0.46377 

0.61836 

0.77295 

0.92753 

1.08212 

1.23671 

1.39130 

0.42667 

0.64000 

0.85333 

1.06667 

1.28000 

1.49333 

1.70667 

1.92000 

1.77778 

2.66667 

3.55556 

4.44445 

5.33333 

6.22222 

7.11111 

8.00000 

0.39480 

0.59220 

0.78960 

0.98700 

1.18440 

1.38180 

1.57920 

1.77660 

0.87324   1.30986 

1.74648 

2.18309 

2.61971 

3.05633 

3.49295 

3.92957 

1.27928 

1.91892 

2.55856 

3.19820 

3.83784 

4.47748 

5.11712 

5.75676 

0.94040 
0.33907 

1.41060 
0.50860 

1.88080 
0.67814 

2.35099 
0.84767 

2.82119 
1.01721 

3.29139 
1.18674 

3.76159 

1.35628 

4.23179 
1.52581 

0.39821   0.59731 

0.79641  i  0.99551 

1.19462 

1.39372   1.59282 

1.79192 

868 


TABLE   IV 


TABLE  IV. 


Elements. 

Found. 

Sought. 

1 

Potassium  .  .  . 

Potassa 

Potassium 

0.83026 

K2O 

K 

Potassium  sulphate 

Potassa 

0.54091 

K2SO4 

K20 

Potassium  chloride 

Potassium 

0.52460 

KC1 

K 

Potassium  chloride 

Potassa 

0.63185 

KC1 

K20 

Potassium  platinic  chloride 

Potassa 

0.19308 

(KCl)2PtCl4 

K20 

Potassium  platinic  chloride 

Potassium  chloride 

0.30557 

(K01)2PtCl4 

KC1 

Silicon    

Silicic  anhydride 

Silicon 

0.46667 

SiO2 

Si 

Silver  

Silver  chloride 

Silver 

0.75270 

AgCl 

Ag 

Silver  chloride 

Silver  oxide 

0.80849 

AgCl 

Ag2O 

Sodium  . 

Soda 

Sodium 

0.74227 

Na20 

Na 

Sodium  sulphate 

Soda 

0.43694 

Na2SO4 

Na2O 

Sodium  chloride 

Soda 

0.53060 

Nad 

Na2O 

Sodium  chloride 

Sodium 

0.39384 

NaCl 

Na 

Sodium  carbonate 

Soda 

0.58522 

Na2CO3 

Na20 

Strontium.  .  .  . 

Strontia 

Strontium 

0.84541 

SrO 

Sr 

Strontium  sulphate 

Strontia 

0.56403 

SrSO4 

SrO 

Strontium  carbonate 

Strontia 

0.70169 

SrCO3 

SrO 

Sulphur  .... 

Barium  sulphate 

Sulphur 

0.13734 

• 

BaSO4 

S 

TABLE   IV. 


869 


(Continued). 


2 

3                    4 

.56789 

1.66051 
1.08183 

2.49077 
1.62274 

3.32103 
2.16366 

4.15128 
2.70457 

4.98154  i   5.81180 
3.24549  ;   3.78640 

6.64206 
432732 

7.47231 

4.86823 

1.04920 

1.57380 

2.09840 

2.62300 

3.14761 

3.67221 

419681 

4.72141 

1.26371 

1.89556 

2.52742 

3.15927 

3.79112 

4.42298 

5.05483 

5.68669 

0.38615 

0.57923 

0.77230 

0.96538 

1.15846  j   1.35153      1.54461 

1.73768 

0.61114 

0.91671 

1.22228 

1.52785 

1.83343 

2.13900 

2.44457 

2.75014 

0.93333 

1.40001 

1.86667 

2.33333 

2.80000 

3.26667 

3.73333 

4.20000 

1.50540 

2.25811 

3.01081 

3.76351 

4.51621 

5.26891 

6.02162 

6  77432 

1.61700 

2.42548 

3.23398 

4.04247 

485096 

5.65946 

6.46795 

7.27645 

1.48454 

0.87387 

2.22680 
1.31081 

2.96907 

1.74775 

3.71134 

2.18468 

4.45361 
2.62162 

5.19588 
3.05856 

5.93814 
3.49550 

6.68041 
3.93243 

1.06120 

1.59179 

2.12239 

2.65299 

3.18359 

3.71419 

4.24478 

4.77538 

0.78769 

1.18154 

1.57538 

1.96923 

2.36308 

2.75692 

3.15077 

3.54461 

1.17044 
1.69082 

1.75566 
2.53623 

2.34088 
3.38164 

2.92610 
4.22705 

3.51132 
5.07247 

4.09654 
5.91788 

4.68176 
6.76329 

5.26698 
7.60870 

1.12807 

1.69210 

2.25613 

2.82017 

3.38420 

3.94823 

4.51226 

5.07630 

1.40339 

2.10508 

2.80678 

3.50848 

4.21017 

4.91186 

5.61356 

6.31526 

0.27468      0.41202 

0.54936 

0.68670 

0.82403 

0.96137 

1.09871  \    1.23605 

870 


TABLE   IV. 


TABLE  IV. 


Elements. 

Found. 

Sought. 

1 

Sulphur  

Arsenious  sulphide 

Sulphur 

0  39024 

As2S3 

S 

Barium  sulphate 
BaSO4 

Sulphuric  anhydride 
S03 

0.34335 

Tin  

Stannic  oxide 

Tin 

0  78667 

SnO2 

Sn 

Stannic  oxide 

Stannous  oxide 

0.89333 

SnO2 

SnO 

Zinc  

Zinc  oxide 

Zinc 

0  80260 

ZnO 

Zn 

Zinc  sulphide 

Zinc  oxide 

0.83515 

ZnS 

ZnO 

Zinc  sulphide 
ZnS 

Zinc 
Zn 

0.67031 

TABLE   IV. 


871 


(Continued). 


2 

u 

4 

5 

6 

7 

8 

9 

0.78049 

1.17073 

1.56097 

1.95122 

2.34146 

2.73170 

3.12194 

3.51219 

0.68670 

1.03004 

1.37339 

1.71674 

2.06009 

2.40344 

2.74678 

3.  09013  ' 

1.57333 

2.36000 

3.14667 

3.93333 

472000 

5.50667 

629334 

7.08000 

• 

1.78667   2.68000 

3.57333 

4.46667 

5.36000 

6.25333 

7.14666 

8.04000 

1.60520   2.40780 

3.21040 

4.01300 

4.81560 

5.61820 

6.42080  '  7.22340 

1.67031   2.50546 

3.34062 

4.17577 

5.01092 

5.84608 

6.68123 

7.51639 

1.34061   2.01092 

2.68123 

3.35154 

4.02184 

4.69215 

5.36246 

6.03276 

872 


TABLES    V. — VI. 


TABLE   V. 

SPECIFIC   GRAVITY  AND  ABSOLUTE  WEIGHT  OF  SEVERAL   GASES. 


Atmospheric  air 

Oxygen 

Hydrogen 

Water,  vapor  of 

Carbon,  vapor  of 

Carbon  dioxide 

Carbon  monoxide. . . . 

Marsh  gas 

Elayl  gas 

Phosphorus,  vapor  of. 
Sulphur,  vapor  of.  . . . 
Hydrosulphuric  acid. 

Iodine,  vapor  of 

Bromine,  vapor  of . . . . 

Chlorine 

Nitrogen 

Ammonia 

Cyanogen , 


Specific  gravity,  atmos- 
pheric air  =  1  -0000. 


1  litre  (1000  cubic  centi- 
metres) of  gas  at  0°  and 
0*76  metre  bar.  pressure 
weighs  grammes. 


1-0000 

1-10832 

0-06927 

0-62343 

0-83124 

1  -52394 

0-96978 

0-55416 

0-96978 

4-29474 

6-64992 

1-17759 

8-78898 

5-53952 

2-45631 

0-96978 

0-58879 

1-80102 


1-29366 
1-43379 
0-08961 
0-80651 
1-07534 
1-97146 

1  -25456 
0-71689 
1-25456 
5-55593 
8-60273 
1-52340 

11-36995 
7-16625 
3-17763 
1-25456 
0-76169 

2  32991 


TABLE  VI. 

COMPARISON  OF  THE  DEGREES  OF  THE  MERCURIAL  THERMOMETER  WITH 
THOSE   OF   THE   AIR   THERMOMETER. 


According  to  MAGNUS. 


Degrees  of  the  mercurial 
thermometer. 


Degrees  of  the  air 
thermometer. 

100 100-00 

150  148-74 

200  197-49 

250 245-39 

300  294-51 

330  .  .  320-92 


ALPHABETICAL  INDEX, 


PAGE 

ACETIC  Aero  (reagent),  see  Qual.  Anal, 

Table  of  specific  gravities 679 

Acidimetry 675 

Air,  analysis  of  atmospheric 722 

Air-pump,  Sprengel's  mercury 639 

Alcohol  (reagent),  see  Qual.  Anal,  and 106 

Alkalimetry 691 

Aluminium 149* 

Determination 240 

Basic  acetate  of 151 

Basic  formate  of 151 

Hydroxide 149 

Oxide 150 

Separation  from  alkali  metals 499 

alkali-earth  metals 500 

chromium 500 

Ammonia  (reagent) 109 

Ammonium 137 

Arsenio-molybdate , , 193 

Carbonate  (reagent),  see  Qual.  Anal. 

Chloride ' 137 

Chloride  (reagent),  see  Qual.  Anal. 

Determination , 217 

Ferrous  sulphate  (reagent)  118 

Molybdate  (reagent),  see  Qual.  Anal. 

Magnesium  arsenate 191 

Nitrate  (reagent) 115 

Oxalate  (reagent),  see  Qual.  Anal. 

Phosphomolybdate 198 

Platinic  chloride 137 

Separation  from  metals  of  group  IV. 507 

other  alkali  metals 481 

Sulphide  (reagent),  see  Qual.  Anal. 
Succinate  (reagent),  see  Qual.  Anal. 

Antimonious  sulphide 186 


874  ALPHABETICAL    INDEX. 

PAGE 

Antimony 185 

Determination 231 

Separation  from  other  metals  of  group  VI 569 

metals  of  groups  I.  — V 554 

Tetroxide 187 

Arsenic,  detection  and  estimation  in  presence,  of  organic  matter 781 

Arsenic  (arsenious  and  arsenic  acids). 

Separation  from  other  metals  of  group  VI 569 

metals  of  groups  I. — V 554 

Arsenic  acid,  determination  344 

Separation  from  other  acids 580 

Arsenious  acid,  determination 344 

Separation  from  other  acids . 580 

arsenic  acid 574 

Oxide 190 

Sulphide 190 

Asbestos  filters 100 

Auric  sulphide 574 

Azotometer,  Schiff's 638 

Balance. 

Barium 1 138 

Acetate  (reagent) 112 

Carbonate  (reagent),  see  Qual.  Anal. 

Carbonate 140 

Chloride  (reagent) 112 

Chromate 194 

Hydroxide  (reagent),  see  Qual.  Anal. 

Determination 227 

Separation  from  other  alkali-earth  metals 493 

alkali  metals 488 

Silicofluoride 141 

Sulphate 138 

Bismuth 180 

Basic  chloride 181 

Basic  nitrate , 181 

Carbonate 181 

Chromate 181 

Determination 318 

Separation  from  other  metals  of  group  V 543 

metals  of  groups  I.— IV 536 

Trioxide 180 

Trisulphide 182 

Borax  fused  (reagent) 114 

Boric  acid 200 

Determination 389 

Separation  from  basic  radicals 392 

Bromine,  determination 436 

Separation  from  acid  radicals  of  group  1 588 

group  II 592 


ALPHABETICAL   IXDEX.  875 

PAGE 

Bunsen's  filtering  apparatus 93 

Burette,  Mohr's 36 

Gay-Lussac's 40 

Giessler's 41 

Cadmium 182 

Carbonate 182 

Determination . . . 323' 

Oxide 182 

Separation  from  other  metals  of  group  Y 543 

metals  of  groups  I. — IY 536 

Sulphide 183 

Calcium 143 

Carbonate 143 

Chloride  (reagent),  see  QuaL  Anal, 

reagent  for  organic  analysis 127 

Determination 232 

Fluoride 200 

Hydroxide  (reagent) 109 

Oxalate  145 

Oxide 146 

Sulphate 143 

Separation  from  the  alkali  metals 488 

other  alkali-earth  metals 493 

Calculation  of  analyses 834 

Carbonic  acid 201 

Determination. ...    403 

in  atmospheric  air 722 

Separation  from  basic  radicals 407 

all  other  acids 587 

Chloric  acid 206 

Determination 476 

Separation  from  basic  radicals 476 

acids  of  groups  I.  and  II 602 

nitric  acid 603 

Chlorine,  determination 428 

in  silicates 589 

(Reagent) 116 

Separation  from  basic  radicals 431 

other  acids  of  group  II 592 

acids  of  group  1 588 

fluorine 590 

Chlorine  water  (reagent),  see  Qiial.  Anal. 

Chlorimetry 698 

Chromic  acid 193 

Determination 355 

Separation  from  basic  radicals 358 

other  acids  of  group  1 580 

Chromium 151 

Determination.  .  242 


876  ALPHABETICAL   INDEX. 

PAGE 

Chromium — Hydroxide 151 

Oxide 152 

Separation  from  alkali  metals 499 

alkali-earth  metals 500 

aluminium 499 

Coal,  analysis. 765 

Cobalt ' -. 161 

Determination „ . 262 

Ore,  assay 731 

Cobaltous  hydroxide * .  < 161 

Sulphate 163 

Sulphide 162 

(Cobaltic  compound),  tripotassium  cobaltic  nitrite 163 

Combustion,  see  Organic  Analysis. 

Copper 177 

Metallic  (reagent  for  organic  analysis) 126 

Determination 311 

Ore,  assay 728 

Separation  from  other  metals  of  group  V 543 

metals  of  groups  I.  — IV. . .   . : - 536 

Cupric  oxide 177 

(Reagent  for  organic  analysis) , 123  and  637 

Sulphide 179 

Cuprous  oxide 179 

Sulphide 180 

Sulphocyanate 179 

Cyanogen,  determination 449- 

Separation  from  basic  radicals 451 

acid  radicals  of  group  II. 600 

group  1 588 

Cylinder,  graduated 32 

Distilled  water. 105 

Dolomite,  analysis. 720 

Drying  precipitates r    . .  84 

Drying  substances  for  analysis 46 — 55 

Ether  (reagent) 106 

Errors  in  gravimetrical  analyses 209 

Evaporation 66 

Ferric  acetate  (basic) 166 

Chloride  (reagent),  see  Qual.  Anal. 

Hydroxide 164 

Formate  (basic) 166 

Oxide 165 

Phosphate 195 

Succinate  (basic) 166 

Ferrous  sulphate  (reagent),  see  Qual.  Anal. 

Sulphide 165 

Ferro-  and  ferricyanogen,  determination 454 

Fertilizers,  analysis 767 


ALPHABETICAL   INDEX.  877 

PAGE 

Filtering  apparatus 77 

Formulae,  calculations  required  for  deducing 844 

Gold 184 

Determination 326 

Separation  from  other  metals  of  group  VI 569 

groups  I. — V 554 

Gooch's  method  of  filtering  and  igniting  precipitates 100 

Guano,  analysis 770 

Gunpowder,  analysis 713 

Hydriodic  acid 204 

Hydrobromic  acid 203 

Hydrochloric  acid 203 

(Reagent) 107 

Hydrocyanic  acid, 205 

Hydrofluoric  acid 200 

Use  for  testing  silica. 422 

Hydrofluosilicic  acid,  determination 372 

(Reagent),  see  Qual.  Anal. 

Hydrosulphuric  acid 205 

Hydrogen  gas  (reagent),  preparation  of 116 

Hydrogen  sulphide  (reagent),  see  QuaL  Anal. 

Igniting  precipitates 71 — 85 

Bunsen's  method 98 

Gooch's  method 100 

lodic  acid,  determination 364 

Iodine,  determination 439 

(Reagent) 120 

Separation  from  basic  radicals 442 

acid  radicals  of  group  1 588 

group  II 592 

Iron 164 

Determination  in  ferric  compounds 275 

Ferrous  compounds 265 

Separation  from  alkali-earth  metals 509 

metals  of  groups  III.  and  IV 512 

Determination  of  ferrous  in  presence  of  ferric 526 

Iron  ore,  partial  analysis 740 

Complete  analysis 753 

Iron,  wrought,  analysis 765 

Pig,  analysis 758 

Lead \ 170 

Acetate  (reagent),  see  QuaL  Anal. 

Arsenate 190 

Carbonate 170 

Chloride 172 

Chromate 193 

Chromate  (reagent  for  organic  analysis) 124 

Determination 297 

Oxalate..  170 


878  ALPHABETICAL   INDEX. 

PAGE 

Lead— Oxide , 171 

(Reagent) 110 

Ore,  assay 730 

Phosphate , 195 

Separation  from  other  metals  of  group  V 543 

metals  of  groups  I. — IV 536 

Sulphide. 173 

Levigation 44 

Limestone,  analysis 720 

Lithium  carbonate 226 

Determination 226 

Phosphate 226 

Separation  from  other  alkali  metals 481 

Sulphate 226 

Litmus 117 

Litre  flask . 31 

Magnesia  (or  magnesium)  mixture  (reagent) 113 

Magnesium 146 

Ammonium  magnesium  phosphate 147 

Determination 237 

Oxide 149 

Phosphate 195 

Pyroarsenate 192 

Pyrophosphate 148 

Separation  from  other  alkali-earth  metals 493 

the  alkali  metals 488 

Sulphate 146 

Manganese 155 

Ammonium  manganese  phosphate 158 

Carbonate 155 

Determination 251 

Dioxide 156 

Hydroxide 156 

Ore,  estimation  of  oxygen  in 705 

Protosesquioxide 156 

Pyrophosphate 159 

Separation  from  alkali-earth  metals 509 

metals  of  groups  III.  and  IV 512 

Measuring  of  gases 25 

Measuring  of  fluids 30 

Mercuric  chloride  (reagent),  see  Qual.  Anal. 

Oxide 1 76 

Sulphide 176 

Mercurous  chromate 194 

Chloride 174 

Phosphate 193 

Mercury 174 

Determination  in  mercuric  compounds 306 

mercurous  compounds 304 


ALPHABETICAL   INDEX.  879 

PAGE 

Mercury — Separation  from  other  metals  in  group  V 548 

metals  of  groups  I. — IV 536 

Metastannic  acid 188 

Metastannic  chloride. . . .  188 

Molybdic  acid,  determination 353 

Nickel 159 

Determination , 258 

Hydroxide 159 

Metallic 160 

Oxide 159 

Sulphate 160 

Sulphide 160 

Separation  from  alkali-earth  metals 509 

metals  of  groups  III.  and  IV 512 

Nickel  ore,  assay 731 

Nitric  acid 206 

(Reage  n  t) 1 06 

Determination 469 

Separation  from  basic  radicals 469 

chloric  acid  603 

acids  of  groups  I.  and  II 602 

Nitrogen 138 

Determination  in  organic  compounds 634,  637  644, 

Nitrohydrochloric  acid  (reagent),  see  Qua!.  Anal. 

Nitrous  acid,  determination 365 

Normal  solutions,  mode  of  preparing 687 

ORGANIC  ANALYSIS 604 

By  combustion  with  cupric  oxide 610 

lead  chromate 620 

oxygen  gas 621 

Organic  analysis  of  compounds  containing  nitrogen 631 

alkalies 664 

alkali-earth  metals 664 

halogens 661 

sulphur 649 

Organic  analysis,  qualitative 606 

Oxalic  acid 200 

Pure  (reagent) 117 

Determination 394 

Separation  from  basic  radicals 395 

Oxygen  gas  (reagent  for  organic  analysis). ...   125 

Palladious  iodide 205 

Palladium,  determination 325 

Phosphoric  acid 195 

Determination 373 

Separation  from  basic  radicals 383 

all  other  acids 582 

Phosphomorybdate  of  ammonium 198 

Phosphorus,  determination  in  organic  compounds 660 


880  ALPHABETICAL   INDEX. 

PAGE 

Pipette,  graduated 33 

Platinic  chloride  (reagent),  see  Qual.  Anal. 

Potassium  platinic  chloride 185 

Sulphide 185 

Platinum 184 

Determination 329 

t  Separation  from  other  metals  of  group  VI 569 

metals  of  groups  I. — V 554 

Potassa  (reagent) 109 

(Fused  reagent  for  organic  analysis) 127 

Solution  (for  organic  analysis) 127 

Potassium 132 

Boro-fluoride. 200 

Chloride , 133 

Cyanide,  see  Qual.  Anal. 

Determination 210 

Dichromate  (reagent),  see  Qual.  Anal. 

Disulphate  (reagent) 118 

Iodide  (reagent) 121 

Nitrate  (reagent),  see  Qual.  Anal. 
Nitrite  (reagent),  see  Qual.  Anal. 

Permanganate  (reagent) 118 

Platinic  chloride 134 

Separation  from  other  alkali  metals 481 

metals  of  group  IV 508 

Silicofluoride 134 

Sulphate  132 

(reagent),  see  Qual.  Anal. 

Precipitates,  separation  from  fluids 75—76 

Precipitation 74 

Eeagents 105 

Rocks,  analysis 714 

Salt,  analysis  of  common 711 

Samples,  selection  of 42 

Mechanical  division  of. . . . , 43 

Selenious  acid,  determination 361 

Separation  of  acid  radicals  from  each  other 579 

Sifting 45 

.Silicates,  analysis 714 — 719 

Decomposition  by  fusion 422 

Separation  of  alkalies  from 426 

Silicic  acid. 201 

Determination ...  419 

Separation  from  basic  radicals 419 

other  acids 586 

Silver 167 

Bromide 203 

Chloride 167 

Cyanide 170 


ALPHABETICAL   INDEX.  881 

PAGE 

Silver — Determination 283 

Iodide 204 

Metallic  (reagent) 122 

Nitrate  (reagent),  see  Qual.  Anal. 

Phosphate 198 

Separation  from  other  metals  of  group  V 543 

metals  of  groups  I. — IV 536 

Sulphide -. 169 

Soda  lime 125 

Soda  lime  for  nitrogen  determinations 126 

Sodium 135 

Acetate  (reagent),  see  Qual.  Anal. 
Carbonate  (reagent),  see  Qual.  Anal. 

Chloride  (reagent) 122 

Chloride 135 

Determination  215 

Hydrogen  sulphide  (reagent),  see  Qual.  Anal. 
Nitrate  (reagent),  see  Qual.  Anal. 
Platinic  chloride  (reagent),  see' Qual.  Anal. 

Platinic  chloride 136 

Separation  from  other  alkali  metals 481 

metals  of  group  IV 508 

Sulphate , 135 

Thiosulphate  (reagent) .    Ill 

Solution  of  substances  for  analysis 63 

Sprengel's  mercury  air-pump 639 

Stannic  oxide 188 

Phosphate 198 

Sulphide 189 

Stannous  chloride  (reagent),  see  Qual.  Anal. 

Sulphide 189 

Steel  analysis 765 

Strontium 141 

Carbonate 142 

Chloride  (reagent) 113 

Determination 230 

Separation  from  the  alkali  metals 488 

other  alkali-earth  metals 493 

Sulphate 141 

Sulphur,  determination 457 

in  organic  compounds 649 — 658 

in  presence  of  carbonates 591 

in  silicates 590 

Separation  from  metals 461 

Sulphuric  acid,  determination 366 

(Reagent),  see  Qual.  Anal,  and 106 

Separation  from  basic  radicals 370 

other  acids 580 

Sulphurous  acid,  determination • 363 


882  ALPHABETICAL   INDEX. 

PAGE 

TABLES  showing 

Atomic  weights 849 

Absorption  of  nitrogen  in  bromized  hypochlorite  solution.  223 

Weights  of  volumes  of  nitrogen 225 

Composition  of  oxides 849 

Strength  of  acids  corresponding  to  various  specific  gravities.  676 
Strength  of  alkalies  corresponding  to  various  specific  gravi- 
ties  . .  691 

for  Calculation  of  analyses 854 — 871 

Tartaric  acid  (reagent),  see  Qual.  Anal. 

Tin,  determination 338 

Thiosulphuric  acid,  determination 364 

Uranium,  determination 281 

Uranyl  (uranic)  acetate  (reagent) 114 

Pyroarsenate 192 

Pyrophosphate 197 

Volumetric  analysis  (general) 102 

VOLUMETRIC  determination  of 

Acids  in  the  free  state,  see  Acidimetry. 
Alkali  hydroxides  and  carbonates,  see  Alka- 
limetry. 

Alkali-earth  metals 697 

Antimony 335 

Arsenic  acid 351,  579 

Arsenious  acid 350 

Bromine  (in  bromides) 437 

free 443 

Cadmium 324 

Calcium 235,  697 

Copper 317 

Chloric  acid 476 

Chlorine  (in  chlorides) 428 

free 434 

Chromic  acid 356,  357 

Cyanogen 450 

Ferric  iron 278—280 

Ferro-  and  ferricyanogen 454 

Ferrous  iron 267 

Fluorine 402 

Iodine  (in  iodides) 440 

free 443 

Lead 303 

Manganese 257 

Mercury 305,  310 

Oxalic  acid 394 

Potassium 214 

Phosphoric  acid 380 

Silver 288 

Sulphuric  acid ' 367 


ALPHABETICAL   INDEX.  883 

PAGE 

VOLUMETRIC  determination  of— Tin 343 

Zinc 737 

Zinc 152 

Carbonate 152 

Determination 247 

Metallic  (reagent) 110  • 

Oxide 153 

Ore,  assay 737 

Separation  from  alkali-earth  metals 509 

metals  of  groups  III.  and  IV 512 

Sulphide 154 


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